The previous chapter described the Spring’s support for AOP using @AspectJ and schema-based aspect definitions. In this chapter we discuss the lower-level Spring AOP APIs and the AOP support used in Spring 1.2 applications. For new applications, we recommend the use of the Spring 2.0 and later AOP support described in the previous chapter, but when working with existing applications, or when reading books and articles, you may come across Spring 1.2 style examples. Spring 4.0 is backwards compatible with Spring 1.2 and everything described in this chapter is fully supported in Spring 4.0.
Let’s look at how Spring handles the crucial pointcut concept.
Spring’s pointcut model enables pointcut reuse independent of advice types. It’s possible to target different advice using the same pointcut.
The org.springframework.aop.Pointcut
interface is the central interface, used to
target advices to particular classes and methods. The complete interface is shown below:
public interface Pointcut { ClassFilter getClassFilter(); MethodMatcher getMethodMatcher(); }
Splitting the Pointcut
interface into two parts allows reuse of class and method
matching parts, and fine-grained composition operations (such as performing a "union"
with another method matcher).
The ClassFilter
interface is used to restrict the pointcut to a given set of target
classes. If the matches()
method always returns true, all target classes will be
matched:
public interface ClassFilter { boolean matches(Class clazz); }
The MethodMatcher
interface is normally more important. The complete interface is
shown below:
public interface MethodMatcher { boolean matches(Method m, Class targetClass); boolean isRuntime(); boolean matches(Method m, Class targetClass, Object[] args); }
The matches(Method, Class)
method is used to test whether this pointcut will ever
match a given method on a target class. This evaluation can be performed when an AOP
proxy is created, to avoid the need for a test on every method invocation. If the
2-argument matches method returns true for a given method, and the isRuntime()
method
for the MethodMatcher returns true, the 3-argument matches method will be invoked on
every method invocation. This enables a pointcut to look at the arguments passed to the
method invocation immediately before the target advice is to execute.
Most MethodMatchers are static, meaning that their isRuntime()
method returns false.
In this case, the 3-argument matches method will never be invoked.
Tip | |
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If possible, try to make pointcuts static, allowing the AOP framework to cache the results of pointcut evaluation when an AOP proxy is created. |
Spring supports operations on pointcuts: notably, union and intersection.
Since 2.0, the most important type of pointcut used by Spring is
org.springframework.aop.aspectj.AspectJExpressionPointcut
. This is a pointcut that
uses an AspectJ supplied library to parse an AspectJ pointcut expression string.
See the previous chapter for a discussion of supported AspectJ pointcut primitives.
Spring provides several convenient pointcut implementations. Some can be used out of the box; others are intended to be subclassed in application-specific pointcuts.
Static pointcuts are based on method and target class, and cannot take into account the method’s arguments. Static pointcuts are sufficient - and best - for most usages. It’s possible for Spring to evaluate a static pointcut only once, when a method is first invoked: after that, there is no need to evaluate the pointcut again with each method invocation.
Let’s consider some static pointcut implementations included with Spring.
One obvious way to specify static pointcuts is regular expressions. Several AOP
frameworks besides Spring make this possible.
org.springframework.aop.support.JdkRegexpMethodPointcut
is a generic regular
expression pointcut, using the regular expression support in JDK 1.4+.
Using the JdkRegexpMethodPointcut
class, you can provide a list of pattern Strings. If
any of these is a match, the pointcut will evaluate to true. (So the result is
effectively the union of these pointcuts.)
The usage is shown below:
<bean id="settersAndAbsquatulatePointcut" class="org.springframework.aop.support.JdkRegexpMethodPointcut"> <property name="patterns"> <list> <value>.*set.*</value> <value>.*absquatulate</value> </list> </property> </bean>
Spring provides a convenience class, RegexpMethodPointcutAdvisor
, that allows us to
also reference an Advice (remember that an Advice can be an interceptor, before advice,
throws advice etc.). Behind the scenes, Spring will use a JdkRegexpMethodPointcut
.
Using RegexpMethodPointcutAdvisor
simplifies wiring, as the one bean encapsulates both
pointcut and advice, as shown below:
<bean id="settersAndAbsquatulateAdvisor" class="org.springframework.aop.support.RegexpMethodPointcutAdvisor"> <property name="advice"> <ref bean="beanNameOfAopAllianceInterceptor"/> </property> <property name="patterns"> <list> <value>.*set.*</value> <value>.*absquatulate</value> </list> </property> </bean>
RegexpMethodPointcutAdvisor can be used with any Advice type.
Dynamic pointcuts are costlier to evaluate than static pointcuts. They take into account method arguments, as well as static information. This means that they must be evaluated with every method invocation; the result cannot be cached, as arguments will vary.
The main example is the control flow
pointcut.
Spring control flow pointcuts are conceptually similar to AspectJ cflow pointcuts,
although less powerful. (There is currently no way to specify that a pointcut executes
below a join point matched by another pointcut.) A control flow pointcut matches the
current call stack. For example, it might fire if the join point was invoked by a method
in the com.mycompany.web
package, or by the SomeCaller
class. Control flow pointcuts
are specified using the org.springframework.aop.support.ControlFlowPointcut
class.
Note | |
---|---|
Control flow pointcuts are significantly more expensive to evaluate at runtime than even other dynamic pointcuts. In Java 1.4, the cost is about 5 times that of other dynamic pointcuts. |
Spring provides useful pointcut superclasses to help you to implement your own pointcuts.
Because static pointcuts are most useful, you’ll probably subclass StaticMethodMatcherPointcut, as shown below. This requires implementing just one abstract method (although it’s possible to override other methods to customize behavior):
class TestStaticPointcut extends StaticMethodMatcherPointcut { public boolean matches(Method m, Class targetClass) { // return true if custom criteria match } }
There are also superclasses for dynamic pointcuts.
You can use custom pointcuts with any advice type in Spring 1.0 RC2 and above.
Because pointcuts in Spring AOP are Java classes, rather than language features (as in AspectJ) it’s possible to declare custom pointcuts, whether static or dynamic. Custom pointcuts in Spring can be arbitrarily complex. However, using the AspectJ pointcut expression language is recommended if possible.
Note | |
---|---|
Later versions of Spring may offer support for "semantic pointcuts" as offered by JAC: for example, "all methods that change instance variables in the target object." |
Let’s now look at how Spring AOP handles advice.
Each advice is a Spring bean. An advice instance can be shared across all advised objects, or unique to each advised object. This corresponds to per-class or per-instance advice.
Per-class advice is used most often. It is appropriate for generic advice such as transaction advisors. These do not depend on the state of the proxied object or add new state; they merely act on the method and arguments.
Per-instance advice is appropriate for introductions, to support mixins. In this case, the advice adds state to the proxied object.
It’s possible to use a mix of shared and per-instance advice in the same AOP proxy.
Spring provides several advice types out of the box, and is extensible to support arbitrary advice types. Let us look at the basic concepts and standard advice types.
The most fundamental advice type in Spring is interception around advice.
Spring is compliant with the AOP Alliance interface for around advice using method interception. MethodInterceptors implementing around advice should implement the following interface:
public interface MethodInterceptor extends Interceptor { Object invoke(MethodInvocation invocation) throws Throwable; }
The MethodInvocation
argument to the invoke()
method exposes the method being
invoked; the target join point; the AOP proxy; and the arguments to the method. The
invoke()
method should return the invocation’s result: the return value of the join
point.
A simple MethodInterceptor
implementation looks as follows:
public class DebugInterceptor implements MethodInterceptor { public Object invoke(MethodInvocation invocation) throws Throwable { System.out.println("Before: invocation=[" + invocation + "]"); Object rval = invocation.proceed(); System.out.println("Invocation returned"); return rval; } }
Note the call to the MethodInvocation’s proceed()
method. This proceeds down the
interceptor chain towards the join point. Most interceptors will invoke this method, and
return its return value. However, a MethodInterceptor, like any around advice, can
return a different value or throw an exception rather than invoke the proceed method.
However, you don’t want to do this without good reason!
Note | |
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MethodInterceptors offer interoperability with other AOP Alliance-compliant AOP implementations. The other advice types discussed in the remainder of this section implement common AOP concepts, but in a Spring-specific way. While there is an advantage in using the most specific advice type, stick with MethodInterceptor around advice if you are likely to want to run the aspect in another AOP framework. Note that pointcuts are not currently interoperable between frameworks, and the AOP Alliance does not currently define pointcut interfaces. |
A simpler advice type is a before advice. This does not need a MethodInvocation
object, since it will only be called before entering the method.
The main advantage of a before advice is that there is no need to invoke the proceed()
method, and therefore no possibility of inadvertently failing to proceed down the
interceptor chain.
The MethodBeforeAdvice
interface is shown below. (Spring’s API design would allow for
field before advice, although the usual objects apply to field interception and it’s
unlikely that Spring will ever implement it).
public interface MethodBeforeAdvice extends BeforeAdvice { void before(Method m, Object[] args, Object target) throws Throwable; }
Note the return type is void
. Before advice can insert custom behavior before the join
point executes, but cannot change the return value. If a before advice throws an
exception, this will abort further execution of the interceptor chain. The exception
will propagate back up the interceptor chain. If it is unchecked, or on the signature of
the invoked method, it will be passed directly to the client; otherwise it will be
wrapped in an unchecked exception by the AOP proxy.
An example of a before advice in Spring, which counts all method invocations:
public class CountingBeforeAdvice implements MethodBeforeAdvice { private int count; public void before(Method m, Object[] args, Object target) throws Throwable { ++count; } public int getCount() { return count; } }
Tip | |
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Before advice can be used with any pointcut. |
Throws advice is invoked after the return of the join point if the join point threw
an exception. Spring offers typed throws advice. Note that this means that the
org.springframework.aop.ThrowsAdvice
interface does not contain any methods: It is a
tag interface identifying that the given object implements one or more typed throws
advice methods. These should be in the form of:
afterThrowing([Method, args, target], subclassOfThrowable)
Only the last argument is required. The method signatures may have either one or four arguments, depending on whether the advice method is interested in the method and arguments. The following classes are examples of throws advice.
The advice below is invoked if a RemoteException
is thrown (including subclasses):
public class RemoteThrowsAdvice implements ThrowsAdvice { public void afterThrowing(RemoteException ex) throws Throwable { // Do something with remote exception } }
The following advice is invoked if a ServletException
is thrown. Unlike the above
advice, it declares 4 arguments, so that it has access to the invoked method, method
arguments and target object:
public class ServletThrowsAdviceWithArguments implements ThrowsAdvice { public void afterThrowing(Method m, Object[] args, Object target, ServletException ex) { // Do something with all arguments } }
The final example illustrates how these two methods could be used in a single class,
which handles both RemoteException
and ServletException
. Any number of throws advice
methods can be combined in a single class.
public static class CombinedThrowsAdvice implements ThrowsAdvice { public void afterThrowing(RemoteException ex) throws Throwable { // Do something with remote exception } public void afterThrowing(Method m, Object[] args, Object target, ServletException ex) { // Do something with all arguments } }
Note | |
---|---|
If a throws-advice method throws an exception itself, it will override the original exception (i.e. change the exception thrown to the user). The overriding exception will typically be a RuntimeException; this is compatible with any method signature. However, if a throws-advice method throws a checked exception, it will have to match the declared exceptions of the target method and is hence to some degree coupled to specific target method signatures. Do not throw an undeclared checked exception that is incompatible with the target method’s signature! |
Tip | |
---|---|
Throws advice can be used with any pointcut. |
An after returning advice in Spring must implement the org.springframework.aop.AfterReturningAdvice interface, shown below:
public interface AfterReturningAdvice extends Advice { void afterReturning(Object returnValue, Method m, Object[] args, Object target) throws Throwable; }
An after returning advice has access to the return value (which it cannot modify), invoked method, methods arguments and target.
The following after returning advice counts all successful method invocations that have not thrown exceptions:
public class CountingAfterReturningAdvice implements AfterReturningAdvice { private int count; public void afterReturning(Object returnValue, Method m, Object[] args, Object target) throws Throwable { ++count; } public int getCount() { return count; } }
This advice doesn’t change the execution path. If it throws an exception, this will be thrown up the interceptor chain instead of the return value.
Tip | |
---|---|
After returning advice can be used with any pointcut. |
Spring treats introduction advice as a special kind of interception advice.
Introduction requires an IntroductionAdvisor
, and an IntroductionInterceptor
,
implementing the following interface:
public interface IntroductionInterceptor extends MethodInterceptor { boolean implementsInterface(Class intf); }
The invoke()
method inherited from the AOP Alliance MethodInterceptor
interface must
implement the introduction: that is, if the invoked method is on an introduced
interface, the introduction interceptor is responsible for handling the method call - it
cannot invoke proceed()
.
Introduction advice cannot be used with any pointcut, as it applies only at class,
rather than method, level. You can only use introduction advice with the
IntroductionAdvisor
, which has the following methods:
public interface IntroductionAdvisor extends Advisor, IntroductionInfo { ClassFilter getClassFilter(); void validateInterfaces() throws IllegalArgumentException; } public interface IntroductionInfo { Class[] getInterfaces(); }
There is no MethodMatcher
, and hence no Pointcut
, associated with introduction
advice. Only class filtering is logical.
The getInterfaces()
method returns the interfaces introduced by this advisor.
The validateInterfaces()
method is used internally to see whether or not the
introduced interfaces can be implemented by the configured IntroductionInterceptor
.
Let’s look at a simple example from the Spring test suite. Let’s suppose we want to introduce the following interface to one or more objects:
public interface Lockable { void lock(); void unlock(); boolean locked(); }
This illustrates a mixin. We want to be able to cast advised objects to Lockable,
whatever their type, and call lock and unlock methods. If we call the lock() method, we
want all setter methods to throw a LockedException
. Thus we can add an aspect that
provides the ability to make objects immutable, without them having any knowledge of it:
a good example of AOP.
Firstly, we’ll need an IntroductionInterceptor
that does the heavy lifting. In this
case, we extend the org.springframework.aop.support.DelegatingIntroductionInterceptor
convenience class. We could implement IntroductionInterceptor directly, but using
DelegatingIntroductionInterceptor
is best for most cases.
The DelegatingIntroductionInterceptor
is designed to delegate an introduction to an
actual implementation of the introduced interface(s), concealing the use of interception
to do so. The delegate can be set to any object using a constructor argument; the
default delegate (when the no-arg constructor is used) is this. Thus in the example
below, the delegate is the LockMixin
subclass of DelegatingIntroductionInterceptor
.
Given a delegate (by default itself), a DelegatingIntroductionInterceptor
instance
looks for all interfaces implemented by the delegate (other than
IntroductionInterceptor), and will support introductions against any of them. It’s
possible for subclasses such as LockMixin
to call the suppressInterface(Class intf)
method to suppress interfaces that should not be exposed. However, no matter how many
interfaces an IntroductionInterceptor
is prepared to support, the
IntroductionAdvisor
used will control which interfaces are actually exposed. An
introduced interface will conceal any implementation of the same interface by the target.
Thus LockMixin
extends DelegatingIntroductionInterceptor
and implements Lockable
itself. The superclass automatically picks up that Lockable can be supported for
introduction, so we don’t need to specify that. We could introduce any number of
interfaces in this way.
Note the use of the locked
instance variable. This effectively adds additional state
to that held in the target object.
public class LockMixin extends DelegatingIntroductionInterceptor implements Lockable { private boolean locked; public void lock() { this.locked = true; } public void unlock() { this.locked = false; } public boolean locked() { return this.locked; } public Object invoke(MethodInvocation invocation) throws Throwable { if (locked() && invocation.getMethod().getName().indexOf("set") == 0) { throw new LockedException(); } return super.invoke(invocation); } }
Often it isn’t necessary to override the invoke()
method: the
DelegatingIntroductionInterceptor
implementation - which calls the delegate method if
the method is introduced, otherwise proceeds towards the join point - is usually
sufficient. In the present case, we need to add a check: no setter method can be invoked
if in locked mode.
The introduction advisor required is simple. All it needs to do is hold a distinct
LockMixin
instance, and specify the introduced interfaces - in this case, just
Lockable
. A more complex example might take a reference to the introduction
interceptor (which would be defined as a prototype): in this case, there’s no
configuration relevant for a LockMixin
, so we simply create it using new
.
public class LockMixinAdvisor extends DefaultIntroductionAdvisor { public LockMixinAdvisor() { super(new LockMixin(), Lockable.class); } }
We can apply this advisor very simply: it requires no configuration. (However, it is
necessary: It’s impossible to use an IntroductionInterceptor
without an
IntroductionAdvisor.) As usual with introductions, the advisor must be per-instance,
as it is stateful. We need a different instance of LockMixinAdvisor
, and hence
LockMixin
, for each advised object. The advisor comprises part of the advised object’s
state.
We can apply this advisor programmatically, using the Advised.addAdvisor()
method, or
(the recommended way) in XML configuration, like any other advisor. All proxy creation
choices discussed below, including "auto proxy creators," correctly handle introductions
and stateful mixins.
In Spring, an Advisor is an aspect that contains just a single advice object associated with a pointcut expression.
Apart from the special case of introductions, any advisor can be used with any advice.
org.springframework.aop.support.DefaultPointcutAdvisor
is the most commonly used
advisor class. For example, it can be used with a MethodInterceptor
, BeforeAdvice
or
ThrowsAdvice
.
It is possible to mix advisor and advice types in Spring in the same AOP proxy. For example, you could use a interception around advice, throws advice and before advice in one proxy configuration: Spring will automatically create the necessary interceptor chain.
If you’re using the Spring IoC container (an ApplicationContext or BeanFactory) for your business objects - and you should be! - you will want to use one of Spring’s AOP FactoryBeans. (Remember that a factory bean introduces a layer of indirection, enabling it to create objects of a different type.)
Note | |
---|---|
The Spring AOP support also uses factory beans under the covers. |
The basic way to create an AOP proxy in Spring is to use the org.springframework.aop.framework.ProxyFactoryBean. This gives complete control over the pointcuts and advice that will apply, and their ordering. However, there are simpler options that are preferable if you don’t need such control.
The ProxyFactoryBean
, like other Spring FactoryBean
implementations, introduces a
level of indirection. If you define a ProxyFactoryBean
with name foo
, what objects
referencing foo
see is not the ProxyFactoryBean
instance itself, but an object
created by the ProxyFactoryBean
's implementation of the getObject()
method. This
method will create an AOP proxy wrapping a target object.
One of the most important benefits of using a ProxyFactoryBean
or another IoC-aware
class to create AOP proxies, is that it means that advices and pointcuts can also be
managed by IoC. This is a powerful feature, enabling certain approaches that are hard to
achieve with other AOP frameworks. For example, an advice may itself reference
application objects (besides the target, which should be available in any AOP
framework), benefiting from all the pluggability provided by Dependency Injection.
In common with most FactoryBean
implementations provided with Spring, the
ProxyFactoryBean
class is itself a JavaBean. Its properties are used to:
Some key properties are inherited from org.springframework.aop.framework.ProxyConfig
(the superclass for all AOP proxy factories in Spring). These key properties include:
proxyTargetClass
: true
if the target class is to be proxied, rather than the
target class' interfaces. If this property value is set to true
, then CGLIB proxies
will be created (but see also Section 10.5.3, “JDK- and CGLIB-based proxies”).
optimize
: controls whether or not aggressive optimizations are applied to proxies
created via CGLIB. One should not blithely use this setting unless one fully
understands how the relevant AOP proxy handles optimization. This is currently used
only for CGLIB proxies; it has no effect with JDK dynamic proxies.
frozen
: if a proxy configuration is frozen
, then changes to the configuration are
no longer allowed. This is useful both as a slight optimization and for those cases
when you don’t want callers to be able to manipulate the proxy (via the Advised
interface) after the proxy has been created. The default value of this property is
false
, so changes such as adding additional advice are allowed.
exposeProxy
: determines whether or not the current proxy should be exposed in a
ThreadLocal
so that it can be accessed by the target. If a target needs to obtain
the proxy and the exposeProxy
property is set to true
, the target can use the
AopContext.currentProxy()
method.
Other properties specific to ProxyFactoryBean
include:
proxyInterfaces
: array of String interface names. If this isn’t supplied, a CGLIB
proxy for the target class will be used (but see also Section 10.5.3, “JDK- and CGLIB-based proxies”).
interceptorNames
: String array of Advisor
, interceptor or other advice names to
apply. Ordering is significant, on a first come-first served basis. That is to say
that the first interceptor in the list will be the first to be able to intercept the
invocation.
The names are bean names in the current factory, including bean names from ancestor
factories. You can’t mention bean references here since doing so would result in the
ProxyFactoryBean
ignoring the singleton setting of the advice.
You can append an interceptor name with an asterisk ( *
). This will result in the
application of all advisor beans with names starting with the part before the asterisk
to be applied. An example of using this feature can be found in Section 10.5.6, “Using global advisors”.
getObject()
method is called. Several FactoryBean
implementations offer
such a method. The default value is true
. If you want to use stateful advice - for
example, for stateful mixins - use prototype advices along with a singleton value of
false
.
This section serves as the definitive documentation on how the ProxyFactoryBean
chooses to create one of either a JDK- and CGLIB-based proxy for a particular target
object (that is to be proxied).
Note | |
---|---|
The behavior of the |
If the class of a target object that is to be proxied (hereafter simply referred to as
the target class) doesn’t implement any interfaces, then a CGLIB-based proxy will be
created. This is the easiest scenario, because JDK proxies are interface based, and no
interfaces means JDK proxying isn’t even possible. One simply plugs in the target bean,
and specifies the list of interceptors via the interceptorNames
property. Note that a
CGLIB-based proxy will be created even if the proxyTargetClass
property of the
ProxyFactoryBean
has been set to false
. (Obviously this makes no sense, and is best
removed from the bean definition because it is at best redundant, and at worst
confusing.)
If the target class implements one (or more) interfaces, then the type of proxy that is
created depends on the configuration of the ProxyFactoryBean
.
If the proxyTargetClass
property of the ProxyFactoryBean
has been set to true
,
then a CGLIB-based proxy will be created. This makes sense, and is in keeping with the
principle of least surprise. Even if the proxyInterfaces
property of the
ProxyFactoryBean
has been set to one or more fully qualified interface names, the fact
that the proxyTargetClass
property is set to true
will cause CGLIB-based
proxying to be in effect.
If the proxyInterfaces
property of the ProxyFactoryBean
has been set to one or more
fully qualified interface names, then a JDK-based proxy will be created. The created
proxy will implement all of the interfaces that were specified in the proxyInterfaces
property; if the target class happens to implement a whole lot more interfaces than
those specified in the proxyInterfaces
property, that is all well and good but those
additional interfaces will not be implemented by the returned proxy.
If the proxyInterfaces
property of the ProxyFactoryBean
has not been set, but
the target class does implement one (or more) interfaces, then the
ProxyFactoryBean
will auto-detect the fact that the target class does actually
implement at least one interface, and a JDK-based proxy will be created. The interfaces
that are actually proxied will be all of the interfaces that the target class
implements; in effect, this is the same as simply supplying a list of each and every
interface that the target class implements to the proxyInterfaces
property. However,
it is significantly less work, and less prone to typos.
Let’s look at a simple example of ProxyFactoryBean
in action. This example involves:
<bean id="personTarget" class="com.mycompany.PersonImpl"> <property name="name" value="Tony"/> <property name="age" value="51"/> </bean> <bean id="myAdvisor" class="com.mycompany.MyAdvisor"> <property name="someProperty" value="Custom string property value"/> </bean> <bean id="debugInterceptor" class="org.springframework.aop.interceptor.DebugInterceptor"> </bean> <bean id="person" class="org.springframework.aop.framework.ProxyFactoryBean"> <property name="proxyInterfaces" value="com.mycompany.Person"/> <property name="target" ref="personTarget"/> <property name="interceptorNames"> <list> <value>myAdvisor</value> <value>debugInterceptor</value> </list> </property> </bean>
Note that the interceptorNames
property takes a list of String: the bean names of the
interceptor or advisors in the current factory. Advisors, interceptors, before, after
returning and throws advice objects can be used. The ordering of advisors is significant.
Note | |
---|---|
You might be wondering why the list doesn’t hold bean references. The reason for this is that if the ProxyFactoryBean’s singleton property is set to false, it must be able to return independent proxy instances. If any of the advisors is itself a prototype, an independent instance would need to be returned, so it’s necessary to be able to obtain an instance of the prototype from the factory; holding a reference isn’t sufficient. |
The "person" bean definition above can be used in place of a Person implementation, as follows:
Person person = (Person) factory.getBean("person");
Other beans in the same IoC context can express a strongly typed dependency on it, as with an ordinary Java object:
<bean id="personUser" class="com.mycompany.PersonUser"> <property name="person"><ref bean="person"/></property> </bean>
The PersonUser
class in this example would expose a property of type Person. As far as
it’s concerned, the AOP proxy can be used transparently in place of a "real" person
implementation. However, its class would be a dynamic proxy class. It would be possible
to cast it to the Advised
interface (discussed below).
It’s possible to conceal the distinction between target and proxy using an anonymous
inner bean, as follows. Only the ProxyFactoryBean
definition is different; the
advice is included only for completeness:
<bean id="myAdvisor" class="com.mycompany.MyAdvisor"> <property name="someProperty" value="Custom string property value"/> </bean> <bean id="debugInterceptor" class="org.springframework.aop.interceptor.DebugInterceptor"/> <bean id="person" class="org.springframework.aop.framework.ProxyFactoryBean"> <property name="proxyInterfaces" value="com.mycompany.Person"/> <!-- Use inner bean, not local reference to target --> <property name="target"> <bean class="com.mycompany.PersonImpl"> <property name="name" value="Tony"/> <property name="age" value="51"/> </bean> </property> <property name="interceptorNames"> <list> <value>myAdvisor</value> <value>debugInterceptor</value> </list> </property> </bean>
This has the advantage that there’s only one object of type Person
: useful if we want
to prevent users of the application context from obtaining a reference to the un-advised
object, or need to avoid any ambiguity with Spring IoC autowiring. There’s also
arguably an advantage in that the ProxyFactoryBean definition is self-contained.
However, there are times when being able to obtain the un-advised target from the
factory might actually be an advantage: for example, in certain test scenarios.
What if you need to proxy a class, rather than one or more interfaces?
Imagine that in our example above, there was no Person
interface: we needed to advise
a class called Person
that didn’t implement any business interface. In this case, you
can configure Spring to use CGLIB proxying, rather than dynamic proxies. Simply set the
proxyTargetClass
property on the ProxyFactoryBean above to true. While it’s best to
program to interfaces, rather than classes, the ability to advise classes that don’t
implement interfaces can be useful when working with legacy code. (In general, Spring
isn’t prescriptive. While it makes it easy to apply good practices, it avoids forcing a
particular approach.)
If you want to, you can force the use of CGLIB in any case, even if you do have interfaces.
CGLIB proxying works by generating a subclass of the target class at runtime. Spring configures this generated subclass to delegate method calls to the original target: the subclass is used to implement the Decorator pattern, weaving in the advice.
CGLIB proxying should generally be transparent to users. However, there are some issues to consider:
Final
methods can’t be advised, as they can’t be overridden.
There’s little performance difference between CGLIB proxying and dynamic proxies. As of Spring 1.0, dynamic proxies are slightly faster. However, this may change in the future. Performance should not be a decisive consideration in this case.
By appending an asterisk to an interceptor name, all advisors with bean names matching the part before the asterisk, will be added to the advisor chain. This can come in handy if you need to add a standard set of global advisors:
<bean id="proxy" class="org.springframework.aop.framework.ProxyFactoryBean"> <property name="target" ref="service"/> <property name="interceptorNames"> <list> <value>global*</value> </list> </property> </bean> <bean id="global_debug" class="org.springframework.aop.interceptor.DebugInterceptor"/> <bean id="global_performance" class="org.springframework.aop.interceptor.PerformanceMonitorInterceptor"/>
Especially when defining transactional proxies, you may end up with many similar proxy definitions. The use of parent and child bean definitions, along with inner bean definitions, can result in much cleaner and more concise proxy definitions.
First a parent, template, bean definition is created for the proxy:
<bean id="txProxyTemplate" abstract="true" class="org.springframework.transaction.interceptor.TransactionProxyFactoryBean"> <property name="transactionManager" ref="transactionManager"/> <property name="transactionAttributes"> <props> <prop key="*">PROPAGATION_REQUIRED</prop> </props> </property> </bean>
This will never be instantiated itself, so may actually be incomplete. Then each proxy which needs to be created is just a child bean definition, which wraps the target of the proxy as an inner bean definition, since the target will never be used on its own anyway.
<bean id="myService" parent="txProxyTemplate"> <property name="target"> <bean class="org.springframework.samples.MyServiceImpl"> </bean> </property> </bean>
It is of course possible to override properties from the parent template, such as in this case, the transaction propagation settings:
<bean id="mySpecialService" parent="txProxyTemplate"> <property name="target"> <bean class="org.springframework.samples.MySpecialServiceImpl"> </bean> </property> <property name="transactionAttributes"> <props> <prop key="get*">PROPAGATION_REQUIRED,readOnly</prop> <prop key="find*">PROPAGATION_REQUIRED,readOnly</prop> <prop key="load*">PROPAGATION_REQUIRED,readOnly</prop> <prop key="store*">PROPAGATION_REQUIRED</prop> </props> </property> </bean>
Note that in the example above, we have explicitly marked the parent bean definition as abstract by using the abstract attribute, as described previously, so that it may not actually ever be instantiated. Application contexts (but not simple bean factories) will by default pre-instantiate all singletons. It is therefore important (at least for singleton beans) that if you have a (parent) bean definition which you intend to use only as a template, and this definition specifies a class, you must make sure to set the abstract attribute to true, otherwise the application context will actually try to pre-instantiate it.
It’s easy to create AOP proxies programmatically using Spring. This enables you to use Spring AOP without dependency on Spring IoC.
The following listing shows creation of a proxy for a target object, with one interceptor and one advisor. The interfaces implemented by the target object will automatically be proxied:
ProxyFactory factory = new ProxyFactory(myBusinessInterfaceImpl);
factory.addAdvice(myMethodInterceptor);
factory.addAdvisor(myAdvisor);
MyBusinessInterface tb = (MyBusinessInterface) factory.getProxy();
The first step is to construct an object of type
org.springframework.aop.framework.ProxyFactory
. You can create this with a target
object, as in the above example, or specify the interfaces to be proxied in an alternate
constructor.
You can add advices (with interceptors as a specialized kind of advice) and/or advisors, and manipulate them for the life of the ProxyFactory. If you add an IntroductionInterceptionAroundAdvisor, you can cause the proxy to implement additional interfaces.
There are also convenience methods on ProxyFactory (inherited from AdvisedSupport
)
which allow you to add other advice types such as before and throws advice.
AdvisedSupport is the superclass of both ProxyFactory and ProxyFactoryBean.
Tip | |
---|---|
Integrating AOP proxy creation with the IoC framework is best practice in most applications. We recommend that you externalize configuration from Java code with AOP, as in general. |
However you create AOP proxies, you can manipulate them using the
org.springframework.aop.framework.Advised
interface. Any AOP proxy can be cast to this
interface, whichever other interfaces it implements. This interface includes the
following methods:
Advisor[] getAdvisors(); void addAdvice(Advice advice) throws AopConfigException; void addAdvice(int pos, Advice advice) throws AopConfigException; void addAdvisor(Advisor advisor) throws AopConfigException; void addAdvisor(int pos, Advisor advisor) throws AopConfigException; int indexOf(Advisor advisor); boolean removeAdvisor(Advisor advisor) throws AopConfigException; void removeAdvisor(int index) throws AopConfigException; boolean replaceAdvisor(Advisor a, Advisor b) throws AopConfigException; boolean isFrozen();
The getAdvisors()
method will return an Advisor for every advisor, interceptor or
other advice type that has been added to the factory. If you added an Advisor, the
returned advisor at this index will be the object that you added. If you added an
interceptor or other advice type, Spring will have wrapped this in an advisor with a
pointcut that always returns true. Thus if you added a MethodInterceptor
, the advisor
returned for this index will be an DefaultPointcutAdvisor
returning your
MethodInterceptor
and a pointcut that matches all classes and methods.
The addAdvisor()
methods can be used to add any Advisor. Usually the advisor holding
pointcut and advice will be the generic DefaultPointcutAdvisor
, which can be used with
any advice or pointcut (but not for introductions).
By default, it’s possible to add or remove advisors or interceptors even once a proxy has been created. The only restriction is that it’s impossible to add or remove an introduction advisor, as existing proxies from the factory will not show the interface change. (You can obtain a new proxy from the factory to avoid this problem.)
A simple example of casting an AOP proxy to the Advised
interface and examining and
manipulating its advice:
Advised advised = (Advised) myObject; Advisor[] advisors = advised.getAdvisors(); int oldAdvisorCount = advisors.length; System.out.println(oldAdvisorCount + " advisors"); // Add an advice like an interceptor without a pointcut // Will match all proxied methods // Can use for interceptors, before, after returning or throws advice advised.addAdvice(new DebugInterceptor()); // Add selective advice using a pointcut advised.addAdvisor(new DefaultPointcutAdvisor(mySpecialPointcut, myAdvice)); assertEquals("Added two advisors", oldAdvisorCount + 2, advised.getAdvisors().length);
Note | |
---|---|
It’s questionable whether it’s advisable (no pun intended) to modify advice on a business object in production, although there are no doubt legitimate usage cases. However, it can be very useful in development: for example, in tests. I have sometimes found it very useful to be able to add test code in the form of an interceptor or other advice, getting inside a method invocation I want to test. (For example, the advice can get inside a transaction created for that method: for example, to run SQL to check that a database was correctly updated, before marking the transaction for roll back.) |
Depending on how you created the proxy, you can usually set a frozen
flag, in which
case the Advised
isFrozen()
method will return true, and any attempts to modify
advice through addition or removal will result in an AopConfigException
. The ability
to freeze the state of an advised object is useful in some cases, for example, to
prevent calling code removing a security interceptor. It may also be used in Spring 1.1
to allow aggressive optimization if runtime advice modification is known not to be
required.
So far we’ve considered explicit creation of AOP proxies using a ProxyFactoryBean
or
similar factory bean.
Spring also allows us to use "auto-proxy" bean definitions, which can automatically proxy selected bean definitions. This is built on Spring "bean post processor" infrastructure, which enables modification of any bean definition as the container loads.
In this model, you set up some special bean definitions in your XML bean definition file
to configure the auto proxy infrastructure. This allows you just to declare the targets
eligible for auto-proxying: you don’t need to use ProxyFactoryBean
.
There are two ways to do this:
The org.springframework.aop.framework.autoproxy
package provides the following
standard auto-proxy creators.
The BeanNameAutoProxyCreator
class is a BeanPostProcessor
that automatically creates
AOP proxies for beans with names matching literal values or wildcards.
<bean class="org.springframework.aop.framework.autoproxy.BeanNameAutoProxyCreator"> <property name="beanNames" value="jdk*,onlyJdk"/> <property name="interceptorNames"> <list> <value>myInterceptor</value> </list> </property> </bean>
As with ProxyFactoryBean
, there is an interceptorNames
property rather than a list
of interceptors, to allow correct behavior for prototype advisors. Named "interceptors"
can be advisors or any advice type.
As with auto proxying in general, the main point of using BeanNameAutoProxyCreator
is
to apply the same configuration consistently to multiple objects, with minimal volume of
configuration. It is a popular choice for applying declarative transactions to multiple
objects.
Bean definitions whose names match, such as "jdkMyBean" and "onlyJdk" in the above
example, are plain old bean definitions with the target class. An AOP proxy will be
created automatically by the BeanNameAutoProxyCreator
. The same advice will be applied
to all matching beans. Note that if advisors are used (rather than the interceptor in
the above example), the pointcuts may apply differently to different beans.
A more general and extremely powerful auto proxy creator is
DefaultAdvisorAutoProxyCreator
. This will automagically apply eligible advisors in the
current context, without the need to include specific bean names in the auto-proxy
advisor’s bean definition. It offers the same merit of consistent configuration and
avoidance of duplication as BeanNameAutoProxyCreator
.
Using this mechanism involves:
DefaultAdvisorAutoProxyCreator
bean definition.
The DefaultAdvisorAutoProxyCreator
will automatically evaluate the pointcut contained
in each advisor, to see what (if any) advice it should apply to each business object
(such as "businessObject1" and "businessObject2" in the example).
This means that any number of advisors can be applied automatically to each business object. If no pointcut in any of the advisors matches any method in a business object, the object will not be proxied. As bean definitions are added for new business objects, they will automatically be proxied if necessary.
Autoproxying in general has the advantage of making it impossible for callers or dependencies to obtain an un-advised object. Calling getBean("businessObject1") on this ApplicationContext will return an AOP proxy, not the target business object. (The "inner bean" idiom shown earlier also offers this benefit.)
<bean class="org.springframework.aop.framework.autoproxy.DefaultAdvisorAutoProxyCreator"/> <bean class="org.springframework.transaction.interceptor.TransactionAttributeSourceAdvisor"> <property name="transactionInterceptor" ref="transactionInterceptor"/> </bean> <bean id="customAdvisor" class="com.mycompany.MyAdvisor"/> <bean id="businessObject1" class="com.mycompany.BusinessObject1"> <!-- Properties omitted --> </bean> <bean id="businessObject2" class="com.mycompany.BusinessObject2"/>
The DefaultAdvisorAutoProxyCreator
is very useful if you want to apply the same advice
consistently to many business objects. Once the infrastructure definitions are in place,
you can simply add new business objects without including specific proxy configuration.
You can also drop in additional aspects very easily - for example, tracing or
performance monitoring aspects - with minimal change to configuration.
The DefaultAdvisorAutoProxyCreator offers support for filtering (using a naming
convention so that only certain advisors are evaluated, allowing use of multiple,
differently configured, AdvisorAutoProxyCreators in the same factory) and ordering.
Advisors can implement the org.springframework.core.Ordered
interface to ensure
correct ordering if this is an issue. The TransactionAttributeSourceAdvisor used in the
above example has a configurable order value; the default setting is unordered.
This is the superclass of DefaultAdvisorAutoProxyCreator. You can create your own
auto-proxy creators by subclassing this class, in the unlikely event that advisor
definitions offer insufficient customization to the behavior of the framework
DefaultAdvisorAutoProxyCreator
.
A particularly important type of auto-proxying is driven by metadata. This produces a
similar programming model to .NET ServicedComponents
. Instead of defining metadata in
XML descriptors, configuration for transaction management and other enterprise services
is held in source-level attributes.
In this case, you use the DefaultAdvisorAutoProxyCreator
, in combination with Advisors
that understand metadata attributes. The metadata specifics are held in the pointcut
part of the candidate advisors, rather than in the auto-proxy creation class itself.
This is really a special case of the DefaultAdvisorAutoProxyCreator
, but deserves
consideration on its own. (The metadata-aware code is in the pointcuts contained in the
advisors, not the AOP framework itself.)
The /attributes
directory of the JPetStore sample application shows the use of
attribute-driven auto-proxying. In this case, there’s no need to use the
TransactionProxyFactoryBean
. Simply defining transactional attributes on business
objects is sufficient, because of the use of metadata-aware pointcuts. The bean
definitions include the following code, in /WEB-INF/declarativeServices.xml
. Note that
this is generic, and can be used outside the JPetStore:
<bean class="org.springframework.aop.framework.autoproxy.DefaultAdvisorAutoProxyCreator"/> <bean class="org.springframework.transaction.interceptor.TransactionAttributeSourceAdvisor"> <property name="transactionInterceptor" ref="transactionInterceptor"/> </bean> <bean id="transactionInterceptor" class="org.springframework.transaction.interceptor.TransactionInterceptor"> <property name="transactionManager" ref="transactionManager"/> <property name="transactionAttributeSource"> <bean class="org.springframework.transaction.interceptor.AttributesTransactionAttributeSource"> <property name="attributes" ref="attributes"/> </bean> </property> </bean> <bean id="attributes" class="org.springframework.metadata.commons.CommonsAttributes"/>
The DefaultAdvisorAutoProxyCreator
bean definition (the name is not significant, hence
it can even be omitted) will pick up all eligible pointcuts in the current application
context. In this case, the "transactionAdvisor" bean definition, of type
TransactionAttributeSourceAdvisor
, will apply to classes or methods carrying a
transaction attribute. The TransactionAttributeSourceAdvisor depends on a
TransactionInterceptor, via constructor dependency. The example resolves this via
autowiring. The AttributesTransactionAttributeSource
depends on an implementation of
the org.springframework.metadata.Attributes
interface. In this fragment, the
"attributes" bean satisfies this, using the Jakarta Commons Attributes API to obtain
attribute information. (The application code must have been compiled using the Commons
Attributes compilation task.)
The /annotation
directory of the JPetStore sample application contains an analogous
example for auto-proxying driven by JDK 1.5+ annotations. The following configuration
enables automatic detection of Spring’s Transactional
annotation, leading to implicit
proxies for beans containing that annotation:
<bean class="org.springframework.aop.framework.autoproxy.DefaultAdvisorAutoProxyCreator"/> <bean class="org.springframework.transaction.interceptor.TransactionAttributeSourceAdvisor"> <property name="transactionInterceptor" ref="transactionInterceptor"/> </bean> <bean id="transactionInterceptor" class="org.springframework.transaction.interceptor.TransactionInterceptor"> <property name="transactionManager" ref="transactionManager"/> <property name="transactionAttributeSource"> <bean class="org.springframework.transaction.annotation.AnnotationTransactionAttributeSource"/> </property> </bean>
The TransactionInterceptor
defined here depends on a PlatformTransactionManager
definition, which is not included in this generic file (although it could be) because it
will be specific to the application’s transaction requirements (typically JTA, as in
this example, or Hibernate, JDO or JDBC):
<bean id="transactionManager" class="org.springframework.transaction.jta.JtaTransactionManager"/>
Tip | |
---|---|
If you require only declarative transaction management, using these generic XML definitions will result in Spring automatically proxying all classes or methods with transaction attributes. You won’t need to work directly with AOP, and the programming model is similar to that of .NET ServicedComponents. |
This mechanism is extensible. It’s possible to do auto-proxying based on custom attributes. You need to:
It’s possible for such advisors to be unique to each advised class (for example, mixins):
they simply need to be defined as prototype, rather than singleton, bean definitions.
For example, the LockMixin
introduction interceptor from the Spring test suite,
shown above, could be used in conjunction with a generic DefaultIntroductionAdvisor
:
<bean id="lockMixin" class="test.mixin.LockMixin" scope="prototype"/> <bean id="lockableAdvisor" class="org.springframework.aop.support.DefaultIntroductionAdvisor" scope="prototype"> <constructor-arg ref="lockMixin"/> </bean>
Note that both lockMixin
and lockableAdvisor
are defined as prototypes.
Spring offers the concept of a TargetSource, expressed in the
org.springframework.aop.TargetSource
interface. This interface is responsible for
returning the "target object" implementing the join point. The TargetSource
implementation is asked for a target instance each time the AOP proxy handles a method
invocation.
Developers using Spring AOP don’t normally need to work directly with TargetSources, but this provides a powerful means of supporting pooling, hot swappable and other sophisticated targets. For example, a pooling TargetSource can return a different target instance for each invocation, using a pool to manage instances.
If you do not specify a TargetSource, a default implementation is used that wraps a local object. The same target is returned for each invocation (as you would expect).
Let’s look at the standard target sources provided with Spring, and how you can use them.
Tip | |
---|---|
When using a custom target source, your target will usually need to be a prototype rather than a singleton bean definition. This allows Spring to create a new target instance when required. |
The org.springframework.aop.target.HotSwappableTargetSource
exists to allow the target
of an AOP proxy to be switched while allowing callers to keep their references to it.
Changing the target source’s target takes effect immediately. The
HotSwappableTargetSource
is threadsafe.
You can change the target via the swap()
method on HotSwappableTargetSource as follows:
HotSwappableTargetSource swapper = (HotSwappableTargetSource) beanFactory.getBean("swapper");
Object oldTarget = swapper.swap(newTarget);
The XML definitions required look as follows:
<bean id="initialTarget" class="mycompany.OldTarget"/> <bean id="swapper" class="org.springframework.aop.target.HotSwappableTargetSource"> <constructor-arg ref="initialTarget"/> </bean> <bean id="swappable" class="org.springframework.aop.framework.ProxyFactoryBean"> <property name="targetSource" ref="swapper"/> </bean>
The above swap()
call changes the target of the swappable bean. Clients who hold a
reference to that bean will be unaware of the change, but will immediately start hitting
the new target.
Although this example doesn’t add any advice - and it’s not necessary to add advice to
use a TargetSource
- of course any TargetSource
can be used in conjunction with
arbitrary advice.
Using a pooling target source provides a similar programming model to stateless session EJBs, in which a pool of identical instances is maintained, with method invocations going to free objects in the pool.
A crucial difference between Spring pooling and SLSB pooling is that Spring pooling can be applied to any POJO. As with Spring in general, this service can be applied in a non-invasive way.
Spring provides out-of-the-box support for Jakarta Commons Pool 1.3, which provides a
fairly efficient pooling implementation. You’ll need the commons-pool Jar on your
application’s classpath to use this feature. It’s also possible to subclass
org.springframework.aop.target.AbstractPoolingTargetSource
to support any other
pooling API.
Sample configuration is shown below:
<bean id="businessObjectTarget" class="com.mycompany.MyBusinessObject" scope="prototype"> ... properties omitted </bean> <bean id="poolTargetSource" class="org.springframework.aop.target.CommonsPoolTargetSource"> <property name="targetBeanName" value="businessObjectTarget"/> <property name="maxSize" value="25"/> </bean> <bean id="businessObject" class="org.springframework.aop.framework.ProxyFactoryBean"> <property name="targetSource" ref="poolTargetSource"/> <property name="interceptorNames" value="myInterceptor"/> </bean>
Note that the target object - "businessObjectTarget" in the example - must be a
prototype. This allows the PoolingTargetSource
implementation to create new instances
of the target to grow the pool as necessary. See the javadocs of
AbstractPoolingTargetSource
and the concrete subclass you wish to use for information
about its properties: "maxSize" is the most basic, and always guaranteed to be present.
In this case, "myInterceptor" is the name of an interceptor that would need to be defined in the same IoC context. However, it isn’t necessary to specify interceptors to use pooling. If you want only pooling, and no other advice, don’t set the interceptorNames property at all.
It’s possible to configure Spring so as to be able to cast any pooled object to the
org.springframework.aop.target.PoolingConfig
interface, which exposes information
about the configuration and current size of the pool through an introduction. You’ll
need to define an advisor like this:
<bean id="poolConfigAdvisor" class="org.springframework.beans.factory.config.MethodInvokingFactoryBean"> <property name="targetObject" ref="poolTargetSource"/> <property name="targetMethod" value="getPoolingConfigMixin"/> </bean>
This advisor is obtained by calling a convenience method on the
AbstractPoolingTargetSource
class, hence the use of MethodInvokingFactoryBean. This
advisor’s name ("poolConfigAdvisor" here) must be in the list of interceptors names in
the ProxyFactoryBean exposing the pooled object.
The cast will look as follows:
PoolingConfig conf = (PoolingConfig) beanFactory.getBean("businessObject"); System.out.println("Max pool size is " + conf.getMaxSize());
Note | |
---|---|
Pooling stateless service objects is not usually necessary. We don’t believe it should be the default choice, as most stateless objects are naturally thread safe, and instance pooling is problematic if resources are cached. |
Simpler pooling is available using auto-proxying. It’s possible to set the TargetSources used by any auto-proxy creator.
Setting up a "prototype" target source is similar to a pooling TargetSource. In this case, a new instance of the target will be created on every method invocation. Although the cost of creating a new object isn’t high in a modern JVM, the cost of wiring up the new object (satisfying its IoC dependencies) may be more expensive. Thus you shouldn’t use this approach without very good reason.
To do this, you could modify the poolTargetSource
definition shown above as follows.
(I’ve also changed the name, for clarity.)
<bean id="prototypeTargetSource" class="org.springframework.aop.target.PrototypeTargetSource"> <property name="targetBeanName" ref="businessObjectTarget"/> </bean>
There’s only one property: the name of the target bean. Inheritance is used in the TargetSource implementations to ensure consistent naming. As with the pooling target source, the target bean must be a prototype bean definition.
ThreadLocal
target sources are useful if you need an object to be created for each
incoming request (per thread that is). The concept of a ThreadLocal
provide a JDK-wide
facility to transparently store resource alongside a thread. Setting up a
ThreadLocalTargetSource
is pretty much the same as was explained for the other types
of target source:
<bean id="threadlocalTargetSource" class="org.springframework.aop.target.ThreadLocalTargetSource"> <property name="targetBeanName" value="businessObjectTarget"/> </bean>
Note | |
---|---|
ThreadLocals come with serious issues (potentially resulting in memory leaks) when
incorrectly using them in a multi-threaded and multi-classloader environments. One
should always consider wrapping a threadlocal in some other class and never directly use
the |
Spring AOP is designed to be extensible. While the interception implementation strategy is presently used internally, it is possible to support arbitrary advice types in addition to the out-of-the-box interception around advice, before, throws advice and after returning advice.
The org.springframework.aop.framework.adapter
package is an SPI package allowing
support for new custom advice types to be added without changing the core framework.
The only constraint on a custom Advice
type is that it must implement the
org.aopalliance.aop.Advice
marker interface.
Please refer to the org.springframework.aop.framework.adapter
javadocs for further
information.
Please refer to the Spring sample applications for further examples of Spring AOP:
Testing is an integral part of enterprise software development. This chapter focuses on the value-add of the IoC principle to unit testing and on the benefits of the Spring Framework’s support for integration testing. (A thorough treatment of testing in the enterprise is beyond the scope of this reference manual.)
Dependency Injection should make your code less dependent on the container than it would
be with traditional Java EE development. The POJOs that make up your application should
be testable in JUnit or TestNG tests, with objects simply instantiated using the new
operator, without Spring or any other container. You can use mock
objects (in conjunction with other valuable testing techniques) to test your code in
isolation. If you follow the architecture recommendations for Spring, the resulting
clean layering and componentization of your codebase will facilitate easier unit
testing. For example, you can test service layer objects by stubbing or mocking DAO or
Repository interfaces, without needing to access persistent data while running unit
tests.
True unit tests typically run extremely quickly, as there is no runtime infrastructure to set up. Emphasizing true unit tests as part of your development methodology will boost your productivity. You may not need this section of the testing chapter to help you write effective unit tests for your IoC-based applications. For certain unit testing scenarios, however, the Spring Framework provides the following mock objects and testing support classes.
The org.springframework.mock.env
package contains mock implementations of the
Environment
and PropertySource
abstractions (see Section 5.13.1, “Bean definition profiles”
and Section 5.13.3, “PropertySource Abstraction”). MockEnvironment
and
MockPropertySource
are useful for developing out-of-container tests for code that
depends on environment-specific properties.
The org.springframework.mock.jndi
package contains an implementation of the JNDI SPI,
which you can use to set up a simple JNDI environment for test suites or stand-alone
applications. If, for example, JDBC DataSource
s get bound to the same JNDI names in
test code as within a Java EE container, you can reuse both application code and
configuration in testing scenarios without modification.
The org.springframework.mock.web
package contains a comprehensive set of Servlet API
mock objects, targeted at usage with Spring’s Web MVC framework, which are useful for
testing web contexts and controllers. These mock objects are generally more convenient
to use than dynamic mock objects such as EasyMock or existing
Servlet API mock objects such as MockObjects.
The org.springframework.test.util
package contains ReflectionTestUtils
, which is a
collection of reflection-based utility methods. Developers use these methods in unit and
integration testing scenarios in which they need to set a non- public
field or invoke
a non- public
setter method when testing application code involving, for example:
private
or protected
field
access as opposed to public
setter methods for properties in a domain entity.
@Autowired
, @Inject
, and @Resource,
which provides dependency injection for private
or protected
fields, setter
methods, and configuration methods.
The org.springframework.test.web
package contains ModelAndViewAssert
, which you can
use in combination with JUnit, TestNG, or any other testing framework for unit tests
dealing with Spring MVC ModelAndView
objects.
Unit testing Spring MVC Controllers | |
---|---|
To test your Spring MVC Note: As of Spring 4.0, the set of mocks in the |
It is important to be able to perform some integration testing without requiring deployment to your application server or connecting to other enterprise infrastructure. This will enable you to test things such as:
The Spring Framework provides first-class support for integration testing in the
spring-test
module. The name of the actual JAR file might include the release version
and might also be in the long org.springframework.test
form, depending on where you
get it from (see the section on Dependency Management for an
explanation). This library includes the org.springframework.test
package, which
contains valuable classes for integration testing with a Spring container. This testing
does not rely on an application server or other deployment environment. Such tests are
slower to run than unit tests but much faster than the equivalent Selenium tests or remote
tests that rely on deployment to an application server.
In Spring 2.5 and later, unit and integration testing support is provided in the form of the annotation-driven Spring TestContext Framework. The TestContext framework is agnostic of the actual testing framework in use, thus allowing instrumentation of tests in various environments including JUnit, TestNG, and so on.
Spring’s integration testing support has the following primary goals:
The next few sections describe each goal and provide links to implementation and configuration details.
The Spring TestContext Framework provides consistent loading of Spring
ApplicationContext
s and WebApplicationContext
s as well as caching of those
contexts. Support for the caching of loaded contexts is important, because startup time
can become an issue — not because of the overhead of Spring itself, but because the
objects instantiated by the Spring container take time to instantiate. For example, a
project with 50 to 100 Hibernate mapping files might take 10 to 20 seconds to load the
mapping files, and incurring that cost before running every test in every test fixture
leads to slower overall test runs that reduce developer productivity.
Test classes typically declare either an array of resource locations for XML
configuration metadata — often in the classpath — or an array of annotated classes
that is used to configure the application. These locations or classes are the same as or
similar to those specified in web.xml
or other deployment configuration files.
By default, once loaded, the configured ApplicationContext
is reused for each test.
Thus the setup cost is incurred only once per test suite, and subsequent test execution
is much faster. In this context, the term test suite means all tests run in the same
JVM — for example, all tests run from an Ant, Maven, or Gradle build for a given
project or module. In the unlikely case that a test corrupts the application context and
requires reloading — for example, by modifying a bean definition or the state of an
application object — the TestContext framework can be configured to reload the
configuration and rebuild the application context before executing the next test.
See the section called “Context management” and the section called “Context caching” with the TestContext framework.
When the TestContext framework loads your application context, it can optionally
configure instances of your test classes via Dependency Injection. This provides a
convenient mechanism for setting up test fixtures using preconfigured beans from your
application context. A strong benefit here is that you can reuse application contexts
across various testing scenarios (e.g., for configuring Spring-managed object graphs,
transactional proxies, DataSource
s, etc.), thus avoiding the need to duplicate
complex test fixture setup for individual test cases.
As an example, consider the scenario where we have a class, HibernateTitleRepository
,
that implements data access logic for a Title
domain entity. We want to write
integration tests that test the following areas:
HibernateTitleRepository
bean correct and present?
HibernateTitleRepository
: does the configured instance of this
class perform as anticipated?
See dependency injection of test fixtures with the TestContext framework.
One common issue in tests that access a real database is their effect on the state of the persistence store. Even when you’re using a development database, changes to the state may affect future tests. Also, many operations — such as inserting or modifying persistent data — cannot be performed (or verified) outside a transaction.
The TestContext framework addresses this issue. By default, the framework will create
and roll back a transaction for each test. You simply write code that can assume the
existence of a transaction. If you call transactionally proxied objects in your tests,
they will behave correctly, according to their configured transactional semantics. In
addition, if a test method deletes the contents of selected tables while running within
the transaction managed for the test, the transaction will roll back by default, and the
database will return to its state prior to execution of the test. Transactional support
is provided to a test via a PlatformTransactionManager
bean defined in the test’s
application context.
If you want a transaction to commit — unusual, but occasionally useful when you want a
particular test to populate or modify the database — the TestContext framework can be
instructed to cause the transaction to commit instead of roll back via the
@TransactionConfiguration
and
@Rollback
annotations.
See transaction management with the TestContext framework.
The Spring TestContext Framework provides several abstract
support classes that
simplify the writing of integration tests. These base test classes provide well-defined
hooks into the testing framework as well as convenient instance variables and methods,
which enable you to access:
ApplicationContext
, for performing explicit bean lookups or testing the state of
the context as a whole.
JdbcTemplate
, for executing SQL statements to query the database. Such queries can
be used to confirm database state both prior to and after execution of
database-related application code, and Spring ensures that such queries run in the
scope of the same transaction as the application code. When used in conjunction with
an ORM tool, be sure to avoid false positives.
In addition, you may want to create your own custom, application-wide superclass with instance variables and methods specific to your project.
See support classes for the TestContext framework.
The org.springframework.test.jdbc
package contains JdbcTestUtils
, which is a
collection of JDBC related utility functions intended to simplify standard database
testing scenarios. Specifically, JdbcTestUtils
provides the following static utility
methods.
countRowsInTable(..)
: counts the number of rows in the given table
countRowsInTableWhere(..)
: counts the number of rows in the given table, using
the provided WHERE
clause
deleteFromTables(..)
: deletes all rows from the specified tables
deleteFromTableWhere(..)
: deletes rows from the given table, using the provided
WHERE
clause
dropTables(..)
: drops the specified tables
Note that AbstractTransactionalJUnit4SpringContextTests
and
AbstractTransactionalTestNGSpringContextTests
provide convenience methods which delegate to the aforementioned methods in
JdbcTestUtils
.
The spring-jdbc
module provides support for configuring and launching an embedded
database which can be used in integration tests that interact with a database. For
details, see Section 13.8, “Embedded database support” and
Section 13.8.8, “Testing data access logic with an embedded database”.
The Spring Framework provides the following set of Spring-specific annotations that you can use in your unit and integration tests in conjunction with the TestContext framework. Refer to the corresponding javadocs for further information, including default attribute values, attribute aliases, and so on.
@ContextConfiguration
Defines class-level metadata that is used to determine how to load and configure an
ApplicationContext
for integration tests. Specifically, @ContextConfiguration
declares the application context resource locations
or the annotated classes
that will be used to load the context.
Resource locations are typically XML configuration files located in the classpath;
whereas, annotated classes are typically @Configuration
classes. However, resource
locations can also refer to files in the file system, and annotated classes can be
component classes, etc.
@ContextConfiguration("/test-config.xml") public class XmlApplicationContextTests { // class body... }
@ContextConfiguration(classes = TestConfig.class) public class ConfigClassApplicationContextTests { // class body... }
As an alternative or in addition to declaring resource locations or annotated classes,
@ContextConfiguration
may be used to declare ApplicationContextInitializer
classes.
@ContextConfiguration(initializers = CustomContextIntializer.class) public class ContextInitializerTests { // class body... }
@ContextConfiguration
may optionally be used to declare the ContextLoader
strategy
as well. Note, however, that you typically do not need to explicitly configure the
loader since the default loader supports either resource locations
or annotated
classes
as well as initializers
.
@ContextConfiguration(locations = "/test-context.xml", loader = CustomContextLoader.class) public class CustomLoaderXmlApplicationContextTests { // class body... }
Note | |
---|---|
|
See the section called “Context management” and the @ContextConfiguration
javadocs for
further details.
@WebAppConfiguration
A class-level annotation that is used to declare that the ApplicationContext
loaded
for an integration test should be a WebApplicationContext
. The mere presence of
@WebAppConfiguration
on a test class ensures that a WebApplicationContext
will be
loaded for the test, using the default value of "file:src/main/webapp"
for the path to
the root of the web application (i.e., the resource base path). The resource base
path is used behind the scenes to create a MockServletContext
which serves as the
ServletContext
for the test’s WebApplicationContext
.
@ContextConfiguration @WebAppConfiguration public class WebAppTests { // class body... }
To override the default, specify a different base resource path via the implicit
value
attribute. Both classpath:
and file:
resource prefixes are supported. If no
resource prefix is supplied the path is assumed to be a file system resource.
@ContextConfiguration @WebAppConfiguration("classpath:test-web-resources") public class WebAppTests { // class body... }
Note that @WebAppConfiguration
must be used in conjunction with
@ContextConfiguration
, either within a single test class or within a test class
hierarchy. See the @WebAppConfiguration
javadocs for further details.
@ContextHierarchy
A class-level annotation that is used to define a hierarchy of ApplicationContext
s
for integration tests. @ContextHierarchy
should be declared with a list of one or more
@ContextConfiguration
instances, each of which defines a level in the context
hierarchy. The following examples demonstrate the use of @ContextHierarchy
within a
single test class; however, @ContextHierarchy
can also be used within a test class
hierarchy.
@ContextHierarchy({ @ContextConfiguration("/parent-config.xml"), @ContextConfiguration("/child-config.xml") }) public class ContextHierarchyTests { // class body... }
@WebAppConfiguration @ContextHierarchy({ @ContextConfiguration(classes = AppConfig.class), @ContextConfiguration(classes = WebConfig.class) }) public class WebIntegrationTests { // class body... }
If you need to merge or override the configuration for a given level of the context
hierarchy within a test class hierarchy, you must explicitly name that level by
supplying the same value to the name
attribute in @ContextConfiguration
at each
corresponding level in the class hierarchy. See
the section called “Context hierarchies” and the @ContextHierarchy
javadocs
for further examples.
@ActiveProfiles
A class-level annotation that is used to declare which bean definition profiles
should be active when loading an ApplicationContext
for test classes.
@ContextConfiguration @ActiveProfiles("dev") public class DeveloperTests { // class body... }
@ContextConfiguration @ActiveProfiles({"dev", "integration"}) public class DeveloperIntegrationTests { // class body... }
Note | |
---|---|
|
See the section called “Context configuration with environment profiles” and the @ActiveProfiles
javadocs
for examples and further details.
@TestPropertySource
A class-level annotation that is used to configure the locations of properties files and
inlined properties to be added to the Environment
's set of PropertySources
for an
ApplicationContext
loaded for an integration test.
Test property sources have higher precedence than those loaded from the operating
system’s environment or Java system properties as well as property sources added by the
application declaratively via @PropertySource
or programmatically. Thus, test property
sources can be used to selectively override properties defined in system and application
property sources. Furthermore, inlined properties have higher precedence than properties
loaded from resource locations.
The following example demonstrates how to declare a properties file from the classpath.
@ContextConfiguration @TestPropertySource("/test.properties") public class MyIntegrationTests { // class body... }
The following example demonstrates how to declare inlined properties.
@ContextConfiguration @TestPropertySource(properties = { "timezone = GMT", "port: 4242" }) public class MyIntegrationTests { // class body... }
@DirtiesContext
Indicates that the underlying Spring ApplicationContext
has been dirtied during
the execution of a test (i.e., modified or corrupted in some manner — for example, by
changing the state of a singleton bean) and should be closed, regardless of whether the
test passed. When an application context is marked dirty, it is removed from the
testing framework’s cache and closed. As a consequence, the underlying Spring container
will be rebuilt for any subsequent test that requires a context with the same
configuration metadata.
@DirtiesContext
can be used as both a class-level and method-level annotation within
the same test class. In such scenarios, the ApplicationContext
is marked as dirty
after any such annotated method as well as after the entire class. If the ClassMode
is
set to AFTER_EACH_TEST_METHOD
, the context is marked dirty after each test method in
the class.
The following examples explain when the context would be dirtied for various configuration scenarios:
After the current test class, when declared on a class with class mode set to
AFTER_CLASS
(i.e., the default class mode).
@DirtiesContext public class ContextDirtyingTests { // some tests that result in the Spring container being dirtied }
After each test method in the current test class, when declared on a class with class
mode set to AFTER_EACH_TEST_METHOD.
@DirtiesContext(classMode = ClassMode.AFTER_EACH_TEST_METHOD) public class ContextDirtyingTests { // some tests that result in the Spring container being dirtied }
After the current test, when declared on a method.
@DirtiesContext @Test public void testProcessWhichDirtiesAppCtx() { // some logic that results in the Spring container being dirtied }
If @DirtiesContext
is used in a test whose context is configured as part of a context
hierarchy via @ContextHierarchy
, the hierarchyMode
flag can be used to control how
the context cache is cleared. By default an exhaustive algorithm will be used that
clears the context cache including not only the current level but also all other context
hierarchies that share an ancestor context common to the current test; all
ApplicationContext
s that reside in a sub-hierarchy of the common ancestor context
will be removed from the context cache and closed. If the exhaustive algorithm is
overkill for a particular use case, the simpler current level algorithm can be
specified instead, as seen below.
@ContextHierarchy({ @ContextConfiguration("/parent-config.xml"), @ContextConfiguration("/child-config.xml") }) public class BaseTests { // class body... } public class ExtendedTests extends BaseTests { @Test @DirtiesContext(hierarchyMode = HierarchyMode.CURRENT_LEVEL) public void test() { // some logic that results in the child context being dirtied } }
For further details regarding the EXHAUSTIVE
and CURRENT_LEVEL
algorithms see the
DirtiesContext.HierarchyMode
javadocs.
@TestExecutionListeners
Defines class-level metadata for configuring which TestExecutionListener
s should be
registered with the TestContextManager
. Typically, @TestExecutionListeners
is used
in conjunction with @ContextConfiguration
.
@ContextConfiguration @TestExecutionListeners({CustomTestExecutionListener.class, AnotherTestExecutionListener.class}) public class CustomTestExecutionListenerTests { // class body... }
@TestExecutionListeners
supports inherited listeners by default. See the javadocs
for an example and further details.
@TransactionConfiguration
Defines class-level metadata for configuring transactional tests. Specifically, the bean
name of the PlatformTransactionManager
that should be used to drive transactions can
be explicitly specified if there are multiple beans of type PlatformTransactionManager
in the test’s ApplicationContext
and if the bean name of the desired
PlatformTransactionManager
is not "transactionManager". In addition, you can change
the defaultRollback
flag to false
. Typically, @TransactionConfiguration
is used in
conjunction with @ContextConfiguration
.
@ContextConfiguration @TransactionConfiguration(transactionManager = "txMgr", defaultRollback = false) public class CustomConfiguredTransactionalTests { // class body... }
Note | |
---|---|
If the default conventions are sufficient for your test configuration, you can avoid
using |
@Rollback
Indicates whether the transaction for the annotated test method should be rolled
back after the test method has completed. If true
, the transaction is rolled back;
otherwise, the transaction is committed. Use @Rollback
to override the default
rollback flag configured at the class level.
@Rollback(false) @Test public void testProcessWithoutRollback() { // ... }
@BeforeTransaction
Indicates that the annotated public void
method should be executed before a
transaction is started for test methods configured to run within a transaction via the
@Transactional
annotation.
@BeforeTransaction public void beforeTransaction() { // logic to be executed before a transaction is started }
@AfterTransaction
Indicates that the annotated public void
method should be executed after a
transaction has ended for test methods configured to run within a transaction via the
@Transactional
annotation.
@AfterTransaction public void afterTransaction() { // logic to be executed after a transaction has ended }
@Sql
Used to annotate a test class or test method to configure SQL scripts to be executed against a given database during integration tests.
@Test @Sql({"/test-schema.sql", "/test-user-data.sql"}) public void userTest { // execute code that relies on the test schema and test data }
See the section called “Executing SQL scripts declaratively with @Sql
” for further details.
@SqlConfig
Defines metadata that is used to determine how to parse and execute SQL scripts
configured via the @Sql
annotation.
@Test @Sql( scripts = "/test-user-data.sql", config = @SqlConfig(commentPrefix = "`", separator = "@@") ) public void userTest { // execute code that relies on the test data }
@SqlGroup
A container annotation that aggregates several @Sql
annotations. Can be used natively,
declaring several nested @Sql
annotations. Can also be used in conjunction with Java
8’s support for repeatable annotations, where @Sql
can simply be declared several times
on the same class or method, implicitly generating this container annotation.
@Test @SqlGroup({ @Sql(scripts = "/test-schema.sql", config = @SqlConfig(commentPrefix = "`")), @Sql("/test-user-data.sql") )} public void userTest { // execute code that uses the test schema and test data }
The following annotations are supported with standard semantics for all configurations of the Spring TestContext Framework. Note that these annotations are not specific to tests and can be used anywhere in the Spring Framework.
@Autowired
@Qualifier
@Resource
(javax.annotation) if JSR-250 is present
@Inject
(javax.inject) if JSR-330 is present
@Named
(javax.inject) if JSR-330 is present
@PersistenceContext
(javax.persistence) if JPA is present
@PersistenceUnit
(javax.persistence) if JPA is present
@Required
@Transactional
JSR-250 Lifecycle Annotations | |
---|---|
In the Spring TestContext Framework If a method within a test class is annotated with |
The following annotations are only supported when used in conjunction with the SpringJUnit4ClassRunner or the JUnit support classes.
@IfProfileValue
Indicates that the annotated test is enabled for a specific testing environment. If the
configured ProfileValueSource
returns a matching value
for the provided name
, the
test is enabled. This annotation can be applied to an entire class or to individual
methods. Class-level usage overrides method-level usage.
@IfProfileValue(name="java.vendor", value="Oracle Corporation") @Test public void testProcessWhichRunsOnlyOnOracleJvm() { // some logic that should run only on Java VMs from Oracle Corporation }
Alternatively, you can configure @IfProfileValue
with a list of values
(with OR
semantics) to achieve TestNG-like support for test groups in a JUnit environment.
Consider the following example:
@IfProfileValue(name="test-groups", values={"unit-tests", "integration-tests"}) @Test public void testProcessWhichRunsForUnitOrIntegrationTestGroups() { // some logic that should run only for unit and integration test groups }
@ProfileValueSourceConfiguration
Class-level annotation that specifies what type of ProfileValueSource
to use when
retrieving profile values configured through the @IfProfileValue
annotation. If
@ProfileValueSourceConfiguration
is not declared for a test,
SystemProfileValueSource
is used by default.
@ProfileValueSourceConfiguration(CustomProfileValueSource.class) public class CustomProfileValueSourceTests { // class body... }
@Timed
Indicates that the annotated test method must finish execution in a specified time period (in milliseconds). If the text execution time exceeds the specified time period, the test fails.
The time period includes execution of the test method itself, any repetitions of the
test (see @Repeat
), as well as any set up or tear down of the test fixture.
@Timed(millis=1000) public void testProcessWithOneSecondTimeout() { // some logic that should not take longer than 1 second to execute }
Spring’s @Timed
annotation has different semantics than JUnit’s @Test(timeout=...)
support. Specifically, due to the manner in which JUnit handles test execution timeouts
(that is, by executing the test method in a separate Thread
), @Test(timeout=...)
preemptively fails the test if the test takes too long. Spring’s @Timed
, on the other
hand, does not preemptively fail the test but rather waits for the test to complete
before failing.
@Repeat
Indicates that the annotated test method must be executed repeatedly. The number of times that the test method is to be executed is specified in the annotation.
The scope of execution to be repeated includes execution of the test method itself as well as any set up or tear down of the test fixture.
@Repeat(10) @Test public void testProcessRepeatedly() { // ... }
As of Spring Framework 4.0, it is possible to use test-related annotations as meta-annotations in order to create custom composed annotations and reduce configuration duplication across a test suite.
Each of the following may be used as meta-annotations in conjunction with the TestContext framework.
@ContextConfiguration
@ContextHierarchy
@ActiveProfiles
@TestPropertySource
@DirtiesContext
@WebAppConfiguration
@TestExecutionListeners
@Transactional
@BeforeTransaction
@AfterTransaction
@TransactionConfiguration
@Rollback
@Sql
@SqlConfig
@SqlGroup
@Repeat
@Timed
@IfProfileValue
@ProfileValueSourceConfiguration
For example, if we discover that we are repeating the following configuration across our JUnit-based test suite…
@RunWith(SpringJUnit4ClassRunner.class) @ContextConfiguration({"/app-config.xml", "/test-data-access-config.xml"}) @ActiveProfiles("dev") @Transactional public class OrderRepositoryTests { } @RunWith(SpringJUnit4ClassRunner.class) @ContextConfiguration({"/app-config.xml", "/test-data-access-config.xml"}) @ActiveProfiles("dev") @Transactional public class UserRepositoryTests { }
We can reduce the above duplication by introducing a custom composed annotation that centralizes the common test configuration like this:
@Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) @ContextConfiguration({"/app-config.xml", "/test-data-access-config.xml"}) @ActiveProfiles("dev") @Transactional public @interface TransactionalDevTest { }
Then we can use our custom @TransactionalDevTest
annotation to simplify the
configuration of individual test classes as follows:
@RunWith(SpringJUnit4ClassRunner.class) @TransactionalDevTest public class OrderRepositoryTests { } @RunWith(SpringJUnit4ClassRunner.class) @TransactionalDevTest public class UserRepositoryTests { }
The Spring TestContext Framework (located in the
org.springframework.test.context
package) provides generic, annotation-driven unit and
integration testing support that is agnostic of the testing framework in use. The
TestContext framework also places a great deal of importance on convention over
configuration with reasonable defaults that can be overridden through annotation-based
configuration.
In addition to generic testing infrastructure, the TestContext framework provides
explicit support for JUnit and TestNG in the form of abstract
support classes. For
JUnit, Spring also provides a custom JUnit Runner
that allows one to write so-called
POJO test classes. POJO test classes are not required to extend a particular class
hierarchy.
The following section provides an overview of the internals of the TestContext framework. If you are only interested in using the framework and not necessarily interested in extending it with your own custom listeners or custom loaders, feel free to go directly to the configuration (context management, dependency injection, transaction management), support classes, and annotation support sections.
The core of the framework consists of the TestContext
and TestContextManager
classes
and the TestExecutionListener
, ContextLoader
, and SmartContextLoader
interfaces. A
TestContextManager
is created on a per-test basis (e.g., for the execution of a single
test method in JUnit). The TestContextManager
in turn manages a TestContext
that
holds the context of the current test. The TestContextManager
also updates the state
of the TestContext
as the test progresses and delegates to TestExecutionListener
s,
which instrument the actual test execution by providing dependency injection, managing
transactions, and so on. A ContextLoader
(or SmartContextLoader
) is responsible for
loading an ApplicationContext
for a given test class. Consult the javadocs and the
Spring test suite for further information and examples of various implementations.
TestContext
: Encapsulates the context in which a test is executed, agnostic of the
actual testing framework in use, and provides context management and caching support
for the test instance for which it is responsible. The TestContext
also delegates to
a ContextLoader
(or SmartContextLoader
) to load an ApplicationContext
if
requested.
TestContextManager
: The main entry point into the Spring TestContext Framework,
which manages a single TestContext
and signals events to all registered
TestExecutionListener
s at well-defined test execution points:
TestExecutionListener
: Defines a listener API for reacting to test execution
events published by the TestContextManager
with which the listener is registered. See
the section called “TestExecutionListener configuration”.
ContextLoader
: Strategy interface introduced in Spring 2.5 for loading an
ApplicationContext
for an integration test managed by the Spring TestContext
Framework.
Implement SmartContextLoader
instead of this interface in order to provide support for
annotated classes, active bean definition profiles, test property sources, context
hierarchies, and WebApplicationContext
s.
SmartContextLoader
: Extension of the ContextLoader
interface introduced in Spring
3.1.
The SmartContextLoader
SPI supersedes the ContextLoader
SPI that was introduced in
Spring 2.5. Specifically, a SmartContextLoader
can choose to process resource
locations
, annotated classes
, or context initializers
. Furthermore, a
SmartContextLoader
can set active bean definition profiles and test property sources in
the context that it loads.
Spring provides the following implementations:
DelegatingSmartContextLoader
: one of two default loaders which delegates internally
to an AnnotationConfigContextLoader
, a GenericXmlContextLoader
, or a
GenericGroovyXmlContextLoader
depending either on the configuration declared for the
test class or on the presence of default locations or default configuration classes.
Groovy support is only enabled if Groovy is on the classpath.
WebDelegatingSmartContextLoader
: one of two default loaders which delegates
internally to an AnnotationConfigWebContextLoader
, a GenericXmlWebContextLoader
, or a
GenericGroovyXmlWebContextLoader
depending either on the configuration declared for the
test class or on the presence of default locations or default configuration classes. A
web ContextLoader
will only be used if @WebAppConfiguration
is present on the test
class. Groovy support is only enabled if Groovy is on the classpath.
AnnotationConfigContextLoader
: loads a standard ApplicationContext
from
annotated classes.
AnnotationConfigWebContextLoader
: loads a WebApplicationContext
from annotated
classes.
GenericGroovyXmlContextLoader
: loads a standard ApplicationContext
from resource
locations that are either Groovy scripts or XML configuration files.
GenericGroovyXmlWebContextLoader
: loads a WebApplicationContext
from resource
locations that are either Groovy scripts or XML configuration files.
GenericXmlContextLoader
: loads a standard ApplicationContext
from XML resource
locations.
GenericXmlWebContextLoader
: loads a WebApplicationContext
from XML resource
locations.
GenericPropertiesContextLoader
: loads a standard ApplicationContext
from Java
Properties files.
The following sections explain how to configure the TestContext framework through annotations and provide working examples of how to write unit and integration tests with the framework.
Spring provides the following TestExecutionListener
implementations that are registered
by default, exactly in this order.
ServletTestExecutionListener
: configures Servlet API mocks for a
WebApplicationContext
DependencyInjectionTestExecutionListener
: provides dependency injection for the test
instance
DirtiesContextTestExecutionListener
: handles the @DirtiesContext
annotation
TransactionalTestExecutionListener
: provides transactional test execution with
default rollback semantics
SqlScriptsTestExecutionListener
: executes SQL scripts configured via the @Sql
annotation
Custom TestExecutionListener
s can be registered for a test class and its subclasses
via the @TestExecutionListeners
annotation. See
annotation support and the javadocs for
@TestExecutionListeners
for details and examples.
Registering custom TestExecutionListener
s via @TestExecutionListeners
is suitable
for custom listeners that are used in limited testing scenarios; however, it can become
cumbersome if a custom listener needs to be used across a test suite. To address this
issue, Spring Framework 4.1 supports automatic discovery of default
TestExecutionListener
implementations via the SpringFactoriesLoader
mechanism.
Specifically, the spring-test
module declares all core default
TestExecutionListener
s under the
org.springframework.test.context.TestExecutionListener
key in its
META-INF/spring.factories
properties file. Third-party frameworks and developers can
contribute their own TestExecutionListener
s to the list of default listeners in the
same manner via their own META-INF/spring.factories
properties file.
When the TestContext framework discovers default TestExecutionListeners
via the
aforementioned SpringFactoriesLoader
mechanism, the instantiated listeners are sorted
using Spring’s AnnotationAwareOrderComparator
which honors Spring’s Ordered
interface
and @Order
annotation for ordering. AbstractTestExecutionListener
and all default
TestExecutionListener
s provided by Spring implement Ordered
with appropriate
values. Third-party frameworks and developers should therefore make sure that their
default TestExecutionListener
s are registered in the proper order by implementing
Ordered
or declaring @Order
. Consult the javadocs for the getOrder()
methods of the
core default TestExecutionListener
s for details on what values are assigned to each
core listener.
If a custom TestExecutionListener
is registered via @TestExecutionListeners
, the
default listeners will not be registered. In most common testing scenarios, this
effectively forces the developer to manually declare all default listeners in addition to
any custom listeners. The following listing demonstrates this style of configuration.
@ContextConfiguration @TestExecutionListeners({ MyCustomTestExecutionListener.class, ServletTestExecutionListener.class, DependencyInjectionTestExecutionListener.class, DirtiesContextTestExecutionListener.class, TransactionalTestExecutionListener.class, SqlScriptsTestExecutionListener.class }) public class MyTest { // class body... }
The challenge with this approach is that it requires that the developer know exactly
which listeners are registered by default. Moreover, the set of default listeners can
change from release to release — for example, SqlScriptsTestExecutionListener
was
introduced in Spring Framework 4.1. Furthermore, third-party frameworks like Spring
Security register their own default TestExecutionListener
s via the aforementioned
automatic discovery mechanism.
To avoid having to be aware of and re-declare all default listeners, the
mergeMode
attribute of @TestExecutionListeners
can be set to
MergeMode.MERGE_WITH_DEFAULTS
. MERGE_WITH_DEFAULTS
indicates that locally declared
listeners should be merged with the default listeners. The merging algorithm ensures that
duplicates are removed from the list and that the resulting set of merged listeners is
sorted according to the semantics of AnnotationAwareOrderComparator
as described in
the section called “Ordering TestExecutionListeners”. If a listener implements Ordered
or is annotated
with @Order
it can influence the position in which it is merged with the defaults;
otherwise, locally declared listeners will simply be appended to the list of default
listeners when merged.
For example, if the MyCustomTestExecutionListener
class in the previous example
configures its order
value (for example, 500
) to be less than the order of the
ServletTestExecutionListener
(which happens to be 1000
), the
MyCustomTestExecutionListener
can then be automatically merged with the list of
defaults in front of the ServletTestExecutionListener
, and the previous example could
be replaced with the following.
@ContextConfiguration @TestExecutionListeners( listeners = MyCustomTestExecutionListener.class, mergeMode = MERGE_WITH_DEFAULTS, ) public class MyTest { // class body... }
Each TestContext
provides context management and caching support for the test instance
it is responsible for. Test instances do not automatically receive access to the
configured ApplicationContext
. However, if a test class implements the
ApplicationContextAware
interface, a reference to the ApplicationContext
is supplied
to the test instance. Note that AbstractJUnit4SpringContextTests
and
AbstractTestNGSpringContextTests
implement ApplicationContextAware
and therefore
provide access to the ApplicationContext
automatically.
@Autowired ApplicationContext | |
---|---|
As an alternative to implementing the @RunWith(SpringJUnit4ClassRunner.class) @ContextConfiguration public class MyTest { @Autowired private ApplicationContext applicationContext; // class body... } Similarly, if your test is configured to load a @RunWith(SpringJUnit4ClassRunner.class) @WebAppConfiguration @ContextConfiguration public class MyWebAppTest { @Autowired private WebApplicationContext wac; // class body... } Dependency injection via |
Test classes that use the TestContext framework do not need to extend any particular
class or implement a specific interface to configure their application context. Instead,
configuration is achieved simply by declaring the @ContextConfiguration
annotation at
the class level. If your test class does not explicitly declare application context
resource locations
or annotated classes
, the configured ContextLoader
determines
how to load a context from a default location or default configuration classes. In
addition to context resource locations
and annotated classes
, an application context
can also be configured via application context initializers
.
The following sections explain how to configure an ApplicationContext
via XML
configuration files, annotated classes (typically @Configuration
classes), or context
initializers using Spring’s @ContextConfiguration
annotation. Alternatively, you can
implement and configure your own custom SmartContextLoader
for advanced use cases.
To load an ApplicationContext
for your tests using XML configuration files, annotate
your test class with @ContextConfiguration
and configure the locations
attribute with
an array that contains the resource locations of XML configuration metadata. A plain or
relative path — for example "context.xml"
— will be treated as a classpath resource
that is relative to the package in which the test class is defined. A path starting with
a slash is treated as an absolute classpath location, for example
"/org/example/config.xml"
. A path which represents a resource URL (i.e., a path
prefixed with classpath:
, file:
, http:
, etc.) will be used as is.
@RunWith(SpringJUnit4ClassRunner.class) // ApplicationContext will be loaded from "/app-config.xml" and // "/test-config.xml" in the root of the classpath @ContextConfiguration(locations={"/app-config.xml", "/test-config.xml"}) public class MyTest { // class body... }
@ContextConfiguration
supports an alias for the locations
attribute through the
standard Java value
attribute. Thus, if you do not need to declare additional
attributes in @ContextConfiguration
, you can omit the declaration of the locations
attribute name and declare the resource locations by using the shorthand format
demonstrated in the following example.
@RunWith(SpringJUnit4ClassRunner.class) @ContextConfiguration({"/app-config.xml", "/test-config.xml"}) public class MyTest { // class body... }
If you omit both the locations
and value
attributes from the @ContextConfiguration
annotation, the TestContext framework will attempt to detect a default XML resource
location. Specifically, GenericXmlContextLoader
and GenericXmlWebContextLoader
detect
a default location based on the name of the test class. If your class is named
com.example.MyTest
, GenericXmlContextLoader
loads your application context from
"classpath:com/example/MyTest-context.xml"
.
package com.example; @RunWith(SpringJUnit4ClassRunner.class) // ApplicationContext will be loaded from // "classpath:com/example/MyTest-context.xml" @ContextConfiguration public class MyTest { // class body... }
To load an ApplicationContext
for your tests using Groovy scripts that utilize the
Groovy Bean Definition DSL, annotate your test class with
@ContextConfiguration
and configure the locations
or value
attribute with an array
that contains the resource locations of Groovy scripts. Resource lookup semantics for
Groovy scripts are the same as those described for XML
configuration files.
Enabling Groovy script support | |
---|---|
Support for using Groovy scripts to load an |
@RunWith(SpringJUnit4ClassRunner.class) // ApplicationContext will be loaded from "/AppConfig.groovy" and // "/TestConfig.groovy" in the root of the classpath @ContextConfiguration({"/AppConfig.groovy", "/TestConfig.Groovy"}) public class MyTest { // class body... }
If you omit both the locations
and value
attributes from the @ContextConfiguration
annotation, the TestContext framework will attempt to detect a default Groovy script.
Specifically, GenericGroovyXmlContextLoader
and GenericGroovyXmlWebContextLoader
detect a default location based on the name of the test class. If your class is named
com.example.MyTest
, the Groovy context loader will load your application context from
"classpath:com/example/MyTestContext.groovy"
.
package com.example; @RunWith(SpringJUnit4ClassRunner.class) // ApplicationContext will be loaded from // "classpath:com/example/MyTestContext.groovy" @ContextConfiguration public class MyTest { // class body... }
Declaring XML config and Groovy scripts simultaneously | |
---|---|
Both XML configuration files and Groovy scripts can be declared simultaneously via the
The following listing demonstrates how to combine both in an integration test. @RunWith(SpringJUnit4ClassRunner.class) // ApplicationContext will be loaded from // "/app-config.xml" and "/TestConfig.groovy" @ContextConfiguration({ "/app-config.xml", "/TestConfig.groovy" }) public class MyTest { // class body... } |
To load an ApplicationContext
for your tests using annotated classes (see
Section 5.12, “Java-based container configuration”), annotate your test class with @ContextConfiguration
and configure the
classes
attribute with an array that contains references to annotated classes.
@RunWith(SpringJUnit4ClassRunner.class) // ApplicationContext will be loaded from AppConfig and TestConfig @ContextConfiguration(classes = {AppConfig.class, TestConfig.class}) public class MyTest { // class body... }
Annotated Classes | |
---|---|
The term annotated class can refer to any of the following.
Consult the javadocs of |
If you omit the classes
attribute from the @ContextConfiguration
annotation, the
TestContext framework will attempt to detect the presence of default configuration
classes. Specifically, AnnotationConfigContextLoader
and
AnnotationConfigWebContextLoader
will detect all static inner classes of the test class
that meet the requirements for configuration class implementations as specified in the
@Configuration
javadocs. In the following example, the OrderServiceTest
class
declares a static inner configuration class named Config
that will be automatically
used to load the ApplicationContext
for the test class. Note that the name of the
configuration class is arbitrary. In addition, a test class can contain more than one
static inner configuration class if desired.
@RunWith(SpringJUnit4ClassRunner.class) // ApplicationContext will be loaded from the // static inner Config class @ContextConfiguration public class OrderServiceTest { @Configuration static class Config { // this bean will be injected into the OrderServiceTest class @Bean public OrderService orderService() { OrderService orderService = new OrderServiceImpl(); // set properties, etc. return orderService; } } @Autowired private OrderService orderService; @Test public void testOrderService() { // test the orderService } }
It may sometimes be desirable to mix XML configuration files, Groovy scripts, and
annotated classes (i.e., typically @Configuration
classes) to configure an
ApplicationContext
for your tests. For example, if you use XML configuration in
production, you may decide that you want to use @Configuration
classes to configure
specific Spring-managed components for your tests, or vice versa.
Furthermore, some third-party frameworks (like Spring Boot) provide first-class support
for loading an ApplicationContext
from different types of resources simultaneously
(e.g., XML configuration files, Groovy scripts, and @Configuration
classes). The Spring
Framework historically has not supported this for standard deployments. Consequently,
most of the SmartContextLoader
implementations that the Spring Framework delivers in
the spring-test
module support only one resource type per test context; however, this
does not mean that you cannot use both. One exception to the general rule is that the
GenericGroovyXmlContextLoader
and GenericGroovyXmlWebContextLoader
support both XML
configuration files and Groovy scripts simultaneously. Furthermore, third-party
frameworks may choose to support the declaration of both locations
and classes
via
@ContextConfiguration
, and with the standard testing support in the TestContext
framework, you have the following options.
If you want to use resource locations (e.g., XML or Groovy) and @Configuration
classes to configure your tests, you will have to pick one as the entry point, and
that one will have to include or import the other. For example, in XML or Groovy scripts
you can include @Configuration
classes via component scanning or define them as normal
Spring beans; whereas, in a @Configuration
class you can use @ImportResource
to
import XML configuration files. Note that this behavior is semantically equivalent to how
you configure your application in production: in production configuration you will define
either a set of XML or Groovy resource locations or a set of @Configuration
classes
that your production ApplicationContext
will be loaded from, but you still have the
freedom to include or import the other type of configuration.
To configure an ApplicationContext
for your tests using context initializers, annotate
your test class with @ContextConfiguration
and configure the initializers
attribute
with an array that contains references to classes that implement
ApplicationContextInitializer
. The declared context initializers will then be used to
initialize the ConfigurableApplicationContext
that is loaded for your tests. Note that
the concrete ConfigurableApplicationContext
type supported by each declared
initializer must be compatible with the type of ApplicationContext
created by the
SmartContextLoader
in use (i.e., typically a GenericApplicationContext
).
Furthermore, the order in which the initializers are invoked depends on whether they
implement Spring’s Ordered
interface, are annotated with Spring’s @Order
or the
standard @Priority
annotation.
@RunWith(SpringJUnit4ClassRunner.class) // ApplicationContext will be loaded from TestConfig // and initialized by TestAppCtxInitializer @ContextConfiguration( classes = TestConfig.class, initializers = TestAppCtxInitializer.class) public class MyTest { // class body... }
It is also possible to omit the declaration of XML configuration files or annotated
classes in @ContextConfiguration
entirely and instead declare only
ApplicationContextInitializer
classes which are then responsible for registering beans
in the context — for example, by programmatically loading bean definitions from XML
files or configuration classes.
@RunWith(SpringJUnit4ClassRunner.class) // ApplicationContext will be initialized by EntireAppInitializer // which presumably registers beans in the context @ContextConfiguration(initializers = EntireAppInitializer.class) public class MyTest { // class body... }
@ContextConfiguration
supports boolean inheritLocations
and inheritInitializers
attributes that denote whether resource locations or annotated classes and context
initializers declared by superclasses should be inherited. The default value for
both flags is true
. This means that a test class inherits the resource locations or
annotated classes as well as the context initializers declared by any superclasses.
Specifically, the resource locations or annotated classes for a test class are appended
to the list of resource locations or annotated classes declared by superclasses.
Similarly, the initializers for a given test class will be added to the set of
initializers defined by test superclasses. Thus, subclasses have the option
of extending the resource locations, annotated classes, or context initializers.
If @ContextConfiguration
's inheritLocations
or inheritInitializers
attribute is
set to false
, the resource locations or annotated classes and the context
initializers, respectively, for the test class shadow and effectively replace the
configuration defined by superclasses.
In the following example that uses XML resource locations, the ApplicationContext
for
ExtendedTest
will be loaded from "base-config.xml" and
"extended-config.xml", in that order. Beans defined in "extended-config.xml" may
therefore override (i.e., replace) those defined in "base-config.xml".
@RunWith(SpringJUnit4ClassRunner.class) // ApplicationContext will be loaded from "/base-config.xml" // in the root of the classpath @ContextConfiguration("/base-config.xml") public class BaseTest { // class body... } // ApplicationContext will be loaded from "/base-config.xml" and // "/extended-config.xml" in the root of the classpath @ContextConfiguration("/extended-config.xml") public class ExtendedTest extends BaseTest { // class body... }
Similarly, in the following example that uses annotated classes, the
ApplicationContext
for ExtendedTest
will be loaded from the BaseConfig
and
ExtendedConfig
classes, in that order. Beans defined in ExtendedConfig
may therefore
override (i.e., replace) those defined in BaseConfig
.
@RunWith(SpringJUnit4ClassRunner.class) // ApplicationContext will be loaded from BaseConfig @ContextConfiguration(classes = BaseConfig.class) public class BaseTest { // class body... } // ApplicationContext will be loaded from BaseConfig and ExtendedConfig @ContextConfiguration(classes = ExtendedConfig.class) public class ExtendedTest extends BaseTest { // class body... }
In the following example that uses context initializers, the ApplicationContext
for
ExtendedTest
will be initialized using BaseInitializer
and
ExtendedInitializer
. Note, however, that the order in which the initializers are
invoked depends on whether they implement Spring’s Ordered
interface, are annotated
with Spring’s @Order
or the standard @Priority
annotation.
@RunWith(SpringJUnit4ClassRunner.class) // ApplicationContext will be initialized by BaseInitializer @ContextConfiguration(initializers = BaseInitializer.class) public class BaseTest { // class body... } // ApplicationContext will be initialized by BaseInitializer // and ExtendedInitializer @ContextConfiguration(initializers = ExtendedInitializer.class) public class ExtendedTest extends BaseTest { // class body... }
Spring 3.1 introduced first-class support in the framework for the notion of
environments and profiles (a.k.a., bean definition profiles), and integration tests
can be configured to activate particular bean definition profiles for various testing
scenarios. This is achieved by annotating a test class with the @ActiveProfiles
annotation and supplying a list of profiles that should be activated when loading the
ApplicationContext
for the test.
Note | |
---|---|
|
Let’s take a look at some examples with XML configuration and @Configuration
classes.
<!-- app-config.xml --> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:jdbc="http://www.springframework.org/schema/jdbc" xmlns:jee="http://www.springframework.org/schema/jee" xsi:schemaLocation="..."> <bean id="transferService" class="com.bank.service.internal.DefaultTransferService"> <constructor-arg ref="accountRepository"/> <constructor-arg ref="feePolicy"/> </bean> <bean id="accountRepository" class="com.bank.repository.internal.JdbcAccountRepository"> <constructor-arg ref="dataSource"/> </bean> <bean id="feePolicy" class="com.bank.service.internal.ZeroFeePolicy"/> <beans profile="dev"> <jdbc:embedded-database id="dataSource"> <jdbc:script location="classpath:com/bank/config/sql/schema.sql"/> <jdbc:script location="classpath:com/bank/config/sql/test-data.sql"/> </jdbc:embedded-database> </beans> <beans profile="production"> <jee:jndi-lookup id="dataSource" jndi-name="java:comp/env/jdbc/datasource"/> </beans> <beans profile="default"> <jdbc:embedded-database id="dataSource"> <jdbc:script location="classpath:com/bank/config/sql/schema.sql"/> </jdbc:embedded-database> </beans> </beans>
package com.bank.service; @RunWith(SpringJUnit4ClassRunner.class) // ApplicationContext will be loaded from "classpath:/app-config.xml" @ContextConfiguration("/app-config.xml") @ActiveProfiles("dev") public class TransferServiceTest { @Autowired private TransferService transferService; @Test public void testTransferService() { // test the transferService } }
When TransferServiceTest
is run, its ApplicationContext
will be loaded from the
app-config.xml
configuration file in the root of the classpath. If you inspect
app-config.xml
you’ll notice that the accountRepository
bean has a dependency on a
dataSource
bean; however, dataSource
is not defined as a top-level bean. Instead,
dataSource
is defined three times: in the production profile, the
dev profile, and the default profile.
By annotating TransferServiceTest
with @ActiveProfiles("dev")
we instruct the Spring
TestContext Framework to load the ApplicationContext
with the active profiles set to
{"dev"}
. As a result, an embedded database will be created and populated with test data,
and the accountRepository
bean will be wired with a reference to the development
DataSource
. And that’s likely what we want in an integration test.
It is sometimes useful to assign beans to a default
profile. Beans within the default profile
are only included when no other profile is specifically activated. This can be used to define
fallback beans to be used in the application’s default state. For example, you may
explicitly provide a data source for dev
and production
profiles, but define an in-memory
data source as a default when neither of these is active.
The following code listings demonstrate how to implement the same configuration and
integration test but using @Configuration
classes instead of XML.
@Configuration @Profile("dev") public class StandaloneDataConfig { @Bean public DataSource dataSource() { return new EmbeddedDatabaseBuilder() .setType(EmbeddedDatabaseType.HSQL) .addScript("classpath:com/bank/config/sql/schema.sql") .addScript("classpath:com/bank/config/sql/test-data.sql") .build(); } }
@Configuration @Profile("production") public class JndiDataConfig { @Bean public DataSource dataSource() throws Exception { Context ctx = new InitialContext(); return (DataSource) ctx.lookup("java:comp/env/jdbc/datasource"); } }
@Configuration @Profile("default") public class DefaultDataConfig { @Bean public DataSource dataSource() { return new EmbeddedDatabaseBuilder() .setType(EmbeddedDatabaseType.HSQL) .addScript("classpath:com/bank/config/sql/schema.sql") .build(); } }
@Configuration public class TransferServiceConfig { @Autowired DataSource dataSource; @Bean public TransferService transferService() { return new DefaultTransferService(accountRepository(), feePolicy()); } @Bean public AccountRepository accountRepository() { return new JdbcAccountRepository(dataSource); } @Bean public FeePolicy feePolicy() { return new ZeroFeePolicy(); } }
package com.bank.service; @RunWith(SpringJUnit4ClassRunner.class) @ContextConfiguration(classes = { TransferServiceConfig.class, StandaloneDataConfig.class, JndiDataConfig.class, DefaultDataConfig.class}) @ActiveProfiles("dev") public class TransferServiceTest { @Autowired private TransferService transferService; @Test public void testTransferService() { // test the transferService } }
In this variation, we have split the XML configuration into four independent
@Configuration
classes:
TransferServiceConfig
: acquires a dataSource
via dependency injection using
@Autowired
StandaloneDataConfig
: defines a dataSource
for an embedded database suitable for
developer tests
JndiDataConfig
: defines a dataSource
that is retrieved from JNDI in a production
environment
DefaultDataConfig
: defines a dataSource
for a default embedded database in case
no profile is active
As with the XML-based configuration example, we still annotate TransferServiceTest
with @ActiveProfiles("dev")
, but this time we specify all four configuration classes
via the @ContextConfiguration
annotation. The body of the test class itself remains
completely unchanged.
It is often the case that a single set of profiles is used across multiple test classes
within a given project. Thus, to avoid duplicate declarations of the @ActiveProfiles
annotation it is possible to declare @ActiveProfiles
once on a base class, and
subclasses will automatically inherit the @ActiveProfiles
configuration from the base
class. In the following example, the declaration of @ActiveProfiles
(as well as other
annotations) has been moved to an abstract superclass, AbstractIntegrationTest
.
package com.bank.service; @RunWith(SpringJUnit4ClassRunner.class) @ContextConfiguration(classes = { TransferServiceConfig.class, StandaloneDataConfig.class, JndiDataConfig.class, DefaultDataConfig.class}) @ActiveProfiles("dev") public abstract class AbstractIntegrationTest { }
package com.bank.service; // "dev" profile inherited from superclass public class TransferServiceTest extends AbstractIntegrationTest { @Autowired private TransferService transferService; @Test public void testTransferService() { // test the transferService } }
@ActiveProfiles
also supports an inheritProfiles
attribute that can be used to
disable the inheritance of active profiles.
package com.bank.service; // "dev" profile overridden with "production" @ActiveProfiles(profiles = "production", inheritProfiles = false) public class ProductionTransferServiceTest extends AbstractIntegrationTest { // test body }
Furthermore, it is sometimes necessary to resolve active profiles for tests programmatically instead of declaratively — for example, based on:
To resolve active bean definition profiles programmatically, simply implement a custom
ActiveProfilesResolver
and register it via the resolver
attribute of
@ActiveProfiles
. The following example demonstrates how to implement and register a
custom OperatingSystemActiveProfilesResolver
. For further information, refer to the
corresponding javadocs.
package com.bank.service; // "dev" profile overridden programmatically via a custom resolver @ActiveProfiles( resolver = OperatingSystemActiveProfilesResolver.class, inheritProfiles = false) public class TransferServiceTest extends AbstractIntegrationTest { // test body }
package com.bank.service.test; public class OperatingSystemActiveProfilesResolver implements ActiveProfilesResolver { @Override String[] resolve(Class<?> testClass) { String profile = ...; // determine the value of profile based on the operating system return new String[] {profile}; } }
Spring 3.1 introduced first-class support in the framework for the notion of an
environment with a hierarchy of property sources, and since Spring 4.1 integration
tests can be configured with test-specific property sources. In contrast to the
@PropertySource
annotation used on @Configuration
classes, the @TestPropertySource
annotation can be declared on a test class to declare resource locations for test
properties files or inlined properties. These test property sources will be added to
the Environment
's set of PropertySources
for the ApplicationContext
loaded for the
annotated integration test.
Note | |
---|---|
Implementations of |
Declaring test property sources
Test properties files can be configured via the locations
or value
attribute of
@TestPropertySource
as shown in the following example.
Both traditional and XML-based properties file formats are supported — for example,
"classpath:/com/example/test.properties"
or "file:///path/to/file.xml"
.
Each path will be interpreted as a Spring Resource
. A plain path — for example,
"test.properties"
— will be treated as a classpath resource that is relative to the
package in which the test class is defined. A path starting with a slash will be treated
as an absolute classpath resource, for example: "/org/example/test.xml"
. A path which
references a URL (e.g., a path prefixed with classpath:
, file:
, http:
, etc.) will
be loaded using the specified resource protocol. Resource location wildcards (e.g.
**/*.properties
) are not permitted: each location must evaluate to exactly one
.properties
or .xml
resource.
@ContextConfiguration @TestPropertySource("/test.properties") public class MyIntegrationTests { // class body... }
Inlined properties in the form of key-value pairs can be configured via the
properties
attribute of @TestPropertySource
as shown in the following example. All
key-value pairs will be added to the enclosing Environment
as a single test
PropertySource
with the highest precedence.
The supported syntax for key-value pairs is the same as the syntax defined for entries in a Java properties file:
"key=value"
"key:value"
"key value"
@ContextConfiguration @TestPropertySource(properties = {"timezone = GMT", "port: 4242"}) public class MyIntegrationTests { // class body... }
Default properties file detection
If @TestPropertySource
is declared as an empty annotation (i.e., without explicit
values for the locations
or properties
attributes), an attempt will be made to detect
a default properties file relative to the class that declared the annotation. For
example, if the annotated test class is com.example.MyTest
, the corresponding default
properties file is "classpath:com/example/MyTest.properties"
. If the default cannot be
detected, an IllegalStateException
will be thrown.
Precedence
Test property sources have higher precedence than those loaded from the operating
system’s environment or Java system properties as well as property sources added by the
application declaratively via @PropertySource
or programmatically. Thus, test property
sources can be used to selectively override properties defined in system and application
property sources. Furthermore, inlined properties have higher precedence than properties
loaded from resource locations.
In the following example, the timezone
and port
properties as well as any properties
defined in "/test.properties"
will override any properties of the same name that are
defined in system and application property sources. Furthermore, if the
"/test.properties"
file defines entries for the timezone
and port
properties those
will be overridden by the inlined properties declared via the properties
attribute.
@ContextConfiguration @TestPropertySource( locations = "/test.properties", properties = {"timezone = GMT", "port: 4242"} ) public class MyIntegrationTests { // class body... }
Inheriting and overriding test property sources
@TestPropertySource
supports boolean inheritLocations
and inheritProperties
attributes that denote whether resource locations for properties files and inlined
properties declared by superclasses should be inherited. The default value for both
flags is true
. This means that a test class inherits the locations and inlined
properties declared by any superclasses. Specifically, the locations and inlined
properties for a test class are appended to the locations and inlined properties declared
by superclasses. Thus, subclasses have the option of extending the locations and
inlined properties. Note that properties that appear later will shadow (i.e..,
override) properties of the same name that appear earlier. In addition, the
aforementioned precedence rules apply for inherited test property sources as well.
If @TestPropertySource
's inheritLocations
or inheritProperties
attribute is set to
false
, the locations or inlined properties, respectively, for the test class shadow
and effectively replace the configuration defined by superclasses.
In the following example, the ApplicationContext
for BaseTest
will be loaded using
only the "base.properties"
file as a test property source. In contrast, the
ApplicationContext
for ExtendedTest
will be loaded using the "base.properties"
and "extended.properties"
files as test property source locations.
@TestPropertySource("base.properties") @ContextConfiguration public class BaseTest { // ... } @TestPropertySource("extended.properties") @ContextConfiguration public class ExtendedTest extends BaseTest { // ... }
In the following example, the ApplicationContext
for BaseTest
will be loaded using only
the inlined key1
property. In contrast, the ApplicationContext
for ExtendedTest
will be
loaded using the inlined key1
and key2
properties.
@TestPropertySource(properties = "key1 = value1") @ContextConfiguration public class BaseTest { // ... } @TestPropertySource(properties = "key2 = value2") @ContextConfiguration public class ExtendedTest extends BaseTest { // ... }
Spring 3.2 introduced support for loading a WebApplicationContext
in integration
tests. To instruct the TestContext framework to load a WebApplicationContext
instead
of a standard ApplicationContext
, simply annotate the respective test class with
@WebAppConfiguration
.
The presence of @WebAppConfiguration
on your test class instructs the TestContext
framework (TCF) that a WebApplicationContext
(WAC) should be loaded for your
integration tests. In the background the TCF makes sure that a MockServletContext
is
created and supplied to your test’s WAC. By default the base resource path for your
MockServletContext
will be set to "src/main/webapp". This is interpreted as a path
relative to the root of your JVM (i.e., normally the path to your project). If you’re
familiar with the directory structure of a web application in a Maven project, you’ll
know that "src/main/webapp" is the default location for the root of your WAR. If you
need to override this default, simply provide an alternate path to the
@WebAppConfiguration
annotation (e.g., @WebAppConfiguration("src/test/webapp")
). If
you wish to reference a base resource path from the classpath instead of the file
system, just use Spring’s classpath: prefix.
Please note that Spring’s testing support for WebApplicationContexts
is on par with
its support for standard ApplicationContexts
. When testing with a
WebApplicationContext
you are free to declare either XML configuration files or
@Configuration
classes via @ContextConfiguration
. You are of course also free to use
any other test annotations such as @TestExecutionListeners
,
@TransactionConfiguration
, @ActiveProfiles
, etc.
The following examples demonstrate some of the various configuration options for loading
a WebApplicationContext
.
Conventions.
@RunWith(SpringJUnit4ClassRunner.class) // defaults to "file:src/main/webapp" @WebAppConfiguration // detects "WacTests-context.xml" in same package // or static nested @Configuration class @ContextConfiguration public class WacTests { //... }
The above example demonstrates the TestContext framework’s support for convention over
configuration. If you annotate a test class with @WebAppConfiguration
without
specifying a resource base path, the resource path will effectively default
to "file:src/main/webapp". Similarly, if you declare @ContextConfiguration
without
specifying resource locations
, annotated classes
, or context initializers
, Spring
will attempt to detect the presence of your configuration using conventions
(i.e., "WacTests-context.xml" in the same package as the WacTests
class or static
nested @Configuration
classes).
Default resource semantics.
@RunWith(SpringJUnit4ClassRunner.class) // file system resource @WebAppConfiguration("webapp") // classpath resource @ContextConfiguration("/spring/test-servlet-config.xml") public class WacTests { //... }
This example demonstrates how to explicitly declare a resource base path with
@WebAppConfiguration
and an XML resource location with @ContextConfiguration
. The
important thing to note here is the different semantics for paths with these two
annotations. By default, @WebAppConfiguration
resource paths are file system based;
whereas, @ContextConfiguration
resource locations are classpath based.
Explicit resource semantics.
@RunWith(SpringJUnit4ClassRunner.class) // classpath resource @WebAppConfiguration("classpath:test-web-resources") // file system resource @ContextConfiguration("file:src/main/webapp/WEB-INF/servlet-config.xml") public class WacTests { //... }
In this third example, we see that we can override the default resource semantics for both annotations by specifying a Spring resource prefix. Contrast the comments in this example with the previous example.
To provide comprehensive web testing support, Spring 3.2 introduced a
ServletTestExecutionListener
that is enabled by default. When testing against a
WebApplicationContext
this TestExecutionListener sets
up default thread-local state via Spring Web’s RequestContextHolder
before each test
method and creates a MockHttpServletRequest
, MockHttpServletResponse
, and
ServletWebRequest
based on the base resource path configured via
@WebAppConfiguration
. ServletTestExecutionListener
also ensures that the
MockHttpServletResponse
and ServletWebRequest
can be injected into the test
instance, and once the test is complete it cleans up thread-local state.
Once you have a WebApplicationContext
loaded for your test you might find that you
need to interact with the web mocks — for example, to set up your test fixture or to
perform assertions after invoking your web component. The following example demonstrates
which mocks can be autowired into your test instance. Note that the
WebApplicationContext
and MockServletContext
are both cached across the test suite;
whereas, the other mocks are managed per test method by the
ServletTestExecutionListener
.
Injecting mocks.
@WebAppConfiguration @ContextConfiguration public class WacTests { @Autowired WebApplicationContext wac; // cached @Autowired MockServletContext servletContext; // cached @Autowired MockHttpSession session; @Autowired MockHttpServletRequest request; @Autowired MockHttpServletResponse response; @Autowired ServletWebRequest webRequest; //... }
Once the TestContext framework loads an ApplicationContext
(or WebApplicationContext
)
for a test, that context will be cached and reused for all subsequent tests that
declare the same unique context configuration within the same test suite. To understand
how caching works, it is important to understand what is meant by unique and test
suite.
An ApplicationContext
can be uniquely identified by the combination of
configuration parameters that are used to load it. Consequently, the unique combination
of configuration parameters are used to generate a key under which the context is
cached. The TestContext framework uses the following configuration parameters to build
the context cache key:
locations
(from @ContextConfiguration)
classes
(from @ContextConfiguration)
contextInitializerClasses
(from @ContextConfiguration)
contextLoader
(from @ContextConfiguration)
parent
(from @ContextHierarchy)
activeProfiles
(from @ActiveProfiles)
propertySourceLocations
(from @TestPropertySource)
propertySourceProperties
(from @TestPropertySource)
resourceBasePath
(from @WebAppConfiguration)
For example, if TestClassA
specifies {"app-config.xml", "test-config.xml"}
for the