bean定义可以跨越多个XML文件是非常有用的。通常每个独立的XML配置文件表示一个逻辑层或者是你架构中的一个模块。

你可以使用应用上下文的构造方法从多个XML片段中加载bean的定义。像上面例子中出现过的一样，构造方法可以接收多个Resource位置。或者可以在bean定义中使用一个或多个<import/>从其他的配置文件引入bean定义。例如：

<beans>
    <import resource="services.xml"/>
    <import resource="resources/messageSource.xml"/>
    <import resource="/resources/themeSource.xml"/>

    <bean id="bean1" class="..."/>
    <bean id="bean2" class="..."/>
</beans>

上面的例子中，外部的bean定义从services.xml、messageSource.xml和themeSource.xml这三个文件中加载。所有的位置路径都是相对于定义执行导入的文件，所以 services.xml必须和当前定义导入的文件在相同的路径下。而messageSource.xml和themeSource.xml必须在当前定义导入的文件路径下的resources路径下。你可以看到，这里忽略了反斜杠，由于这里的路径是相对的，因此建议 不使用反斜杠。这些被引入文件的内容会被导入进来，包含顶层的<beans/>元素，它必须是一个符合Spring架构的有效的XML bean定义。

	Note
	使用一个相对"../"路径引用父目录中的配置是允许的，但是不推荐这么做。如果这么做就产生了一个当前应用外的引用依赖。特别不推荐在使用"classpath:"路径的时候，在运行的时候解析选择“最近”的classpath跟路径，然后在找父目录。Classpath配置的更改可能会导致选择一个不同的、错误的目录。 通常情况下，你可以使用完全限定的资源位置来代替相对路径，例如："file:C:/config/services.xml"或"classpath:/config/services.xml"。但是请注意，你的应用可能和一个特定的绝对路径耦合了。通常更合适的方式是通过间接的方式来使用绝对路径，例如通过"${…}"占位符，在运行时解析JVM的系统属性。

In a bean definition itself, you can supply more than one name for the bean, by using a combination of up to one name specified by the id attribute, and any number of other names in the name attribute. These names can be equivalent aliases to the same bean, and are useful for some situations, such as allowing each component in an application to refer to a common dependency by using a bean name that is specific to that component itself.

Specifying all aliases where the bean is actually defined is not always adequate, however. It is sometimes desirable to introduce an alias for a bean that is defined elsewhere. This is commonly the case in large systems where configuration is split amongst each subsystem, each subsystem having its own set of object definitions. In XML-based configuration metadata, you can use the <alias/> element to accomplish this.

<alias name="fromName" alias="toName"/>

In this case, a bean in the same container which is named fromName, may also, after the use of this alias definition, be referred to as toName.

For example, the configuration metadata for subsystem A may refer to a DataSource via the name subsystemA-dataSource. The configuration metadata for subsystem B may refer to a DataSource via the name subsystemB-dataSource. When composing the main application that uses both these subsystems the main application refers to the DataSource via the name myApp-dataSource. To have all three names refer to the same object you add to the MyApp configuration metadata the following aliases definitions:

<alias name="subsystemA-dataSource" alias="subsystemB-dataSource"/>
<alias name="subsystemA-dataSource" alias="myApp-dataSource" />

Now each component and the main application can refer to the dataSource through a name that is unique and guaranteed not to clash with any other definition (effectively creating a namespace), yet they refer to the same bean.

When you create a bean by the constructor approach, all normal classes are usable by and compatible with Spring. That is, the class being developed does not need to implement any specific interfaces or to be coded in a specific fashion. Simply specifying the bean class should suffice. However, depending on what type of IoC you use for that specific bean, you may need a default (empty) constructor.

The Spring IoC container can manage virtually any class you want it to manage; it is not limited to managing true JavaBeans. Most Spring users prefer actual JavaBeans with only a default (no-argument) constructor and appropriate setters and getters modeled after the properties in the container. You can also have more exotic non-bean-style classes in your container. If, for example, you need to use a legacy connection pool that absolutely does not adhere to the JavaBean specification, Spring can manage it as well.

With XML-based configuration metadata you can specify your bean class as follows:

<bean id="exampleBean" class="examples.ExampleBean"/>

<bean name="anotherExample" class="examples.ExampleBeanTwo"/>

For details about the mechanism for supplying arguments to the constructor (if required) and setting object instance properties after the object is constructed, see Injecting Dependencies.

When defining a bean that you create with a static factory method, you use the class attribute to specify the class containing the static factory method and an attribute named factory-method to specify the name of the factory method itself. You should be able to call this method (with optional arguments as described later) and return a live object, which subsequently is treated as if it had been created through a constructor. One use for such a bean definition is to call static factories in legacy code.

The following bean definition specifies that the bean will be created by calling a factory-method. The definition does not specify the type (class) of the returned object, only the class containing the factory method. In this example, the createInstance() method must be a static method.

<bean id="clientService"
    class="examples.ClientService"
    factory-method="createInstance"/>

public class ClientService {
    private static ClientService clientService = new ClientService();
    private ClientService() {}

    public static ClientService createInstance() {
        return clientService;
    }
}

For details about the mechanism for supplying (optional) arguments to the factory method and setting object instance properties after the object is returned from the factory, see Dependencies and configuration in detail.

Similar to instantiation through a static factory method, instantiation with an instance factory method invokes a non-static method of an existing bean from the container to create a new bean. To use this mechanism, leave the class attribute empty, and in the factory-bean attribute, specify the name of a bean in the current (or parent/ancestor) container that contains the instance method that is to be invoked to create the object. Set the name of the factory method itself with the factory-method attribute.

<!-- the factory bean, which contains a method called createInstance() -->
<bean id="serviceLocator" class="examples.DefaultServiceLocator">
    <!-- inject any dependencies required by this locator bean -->
</bean>

<!-- the bean to be created via the factory bean -->
<bean id="clientService"
    factory-bean="serviceLocator"
    factory-method="createClientServiceInstance"/>

public class DefaultServiceLocator {

    private static ClientService clientService = new ClientServiceImpl();
    private DefaultServiceLocator() {}

    public ClientService createClientServiceInstance() {
        return clientService;
    }
}

One factory class can also hold more than one factory method as shown here:

<bean id="serviceLocator" class="examples.DefaultServiceLocator">
    <!-- inject any dependencies required by this locator bean -->
</bean>

<bean id="clientService"
    factory-bean="serviceLocator"
    factory-method="createClientServiceInstance"/>

<bean id="accountService"
    factory-bean="serviceLocator"
    factory-method="createAccountServiceInstance"/>

public class DefaultServiceLocator {

    private static ClientService clientService = new ClientServiceImpl();
    private static AccountService accountService = new AccountServiceImpl();

    private DefaultServiceLocator() {}

    public ClientService createClientServiceInstance() {
        return clientService;
    }

    public AccountService createAccountServiceInstance() {
        return accountService;
    }

}

This approach shows that the factory bean itself can be managed and configured through dependency injection (DI). See Dependencies and configuration in detail.

	Note
	In Spring documentation, factory bean refers to a bean that is configured in the Spring container that will create objects through an instance or static factory method. By contrast, FactoryBean (notice the capitalization) refers to a Spring-specific FactoryBean.

基于构造器注入 DI通过调用带参数的构造器来实现，每个参数代表着一个依赖关系。此外，还可通过给 静态 工厂方法传参数来构造bean。接下来的介绍将认为给构造器传参数和给静态工厂方法传参数是类似的。下面展示了只能使用构造器来注入依赖关系的例子。请注意这个类并没有什么 特别 之处,它只是个普通的POJO，不依赖于特殊的接口，抽象类或者注解。

public class SimpleMovieLister {

    // the SimpleMovieLister has a dependency on a MovieFinder
    private MovieFinder movieFinder;

    // a constructor so that the Spring container can inject a MovieFinder
    public SimpleMovieLister(MovieFinder movieFinder) {
        this.movieFinder = movieFinder;
    }

    // business logic that actually uses the injected MovieFinder is omitted...

}

package x.y;

public class Foo {

    public Foo(Bar bar, Baz baz) {
        // ...
    }

}

<beans>
    <bean id="foo" class="x.y.Foo">
        <constructor-arg ref="bar"/>
        <constructor-arg ref="baz"/>
    </bean>

    <bean id="bar" class="x.y.Bar"/>

    <bean id="baz" class="x.y.Baz"/>
</beans>

package examples;

public class ExampleBean {

    // Number of years to calculate the Ultimate Answer
    private int years;

    // The Answer to Life, the Universe, and Everything
    private String ultimateAnswer;

    public ExampleBean(int years, String ultimateAnswer) {
        this.years = years;
        this.ultimateAnswer = ultimateAnswer;
    }

}

<bean id="exampleBean" class="examples.ExampleBean">
    <constructor-arg type="int" value="7500000"/>
    <constructor-arg type="java.lang.String" value="42"/>
</bean>

<bean id="exampleBean" class="examples.ExampleBean">
    <constructor-arg index="0" value="7500000"/>
    <constructor-arg index="1" value="42"/>
</bean>

<bean id="exampleBean" class="examples.ExampleBean">
    <constructor-arg name="years" value="7500000"/>
    <constructor-arg name="ultimateAnswer" value="42"/>
</bean>

package examples;

public class ExampleBean {

    // Fields omitted

    @ConstructorProperties({"years", "ultim