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6, IoC
7, Resources
8, Validation, Data Binding, and Type Conversion
9, Spring Expression Language (SpEL)
10, Aspect Oriented Programming with Spring
11, Spring AOP APIs

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1.基于注解的配置，Spring 2.5引入了基于注解配置元数据的形式。
2.基于Java的配置，从Spring 3.0开始，Spring JavaConfig项目提供的许多特性成为了Spring框架核心的一部分。因此，可以在应用程序类的外部通过Java定义bean而不是在XML文件中。使用这些新特性，请参考@Configuration, @Bean, @Import和@DepensOn注解。

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<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="..." class="...">
        <!-- collaborators and configuration for this bean go here -->
    </bean>

    <bean id="..." class="...">
        <!-- collaborators and configuration for this bean go here -->
    </bean>

    <!-- more bean definitions go here -->

</beans>

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ApplicationContext context = new ClassPathXmlApplicationContext(new String[] {"services.xml", "daos.xml"});

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<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd">

    <!-- services -->

    <bean id="petStore" class="org.springframework.samples.jpetstore.services.PetStoreServiceImpl">
        <property name="accountDao" ref="accountDao"/>
        <property name="itemDao" ref="itemDao"/>
        <!-- additional collaborators and configuration for this bean go here -->
    </bean>

    <!-- more bean definitions for services go here -->

</beans>

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<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="accountDao"     class="org.springframework.samples.jpetstore.dao.jpa.JpaAccountDao">
    <!-- additional collaborators and configuration for this bean go here -->
    </bean>

    <bean id="itemDao" class="org.springframework.samples.jpetstore.dao.jpa.JpaItemDao">
    <!-- additional collaborators and configuration for this bean go here -->
    </bean>

    <!-- more bean definitions for data access objects go here -->

</beans>

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

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

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可以使用“../”路径的形式引用父目录的文件，但这是不推荐的。这样做会在当前应用之外的文件上创建一个依赖。尤其是这种引用不推荐放在“classpath:”URL中（例如，“classpath:../services.xml”），在运行时会选择最近的classpath的根目录，然后再在其父目录中寻找。classpath配置改变可能会导致选择了不同的错误的目录。 
可以总是使用全路径定位资源代替相对路径，例如“file:C:/config/services.xml”或“classpath:/config/services.xml”。然而，注意这样会把应用程序的配置与特定的绝对路径耦合了。一般地，可以间接配置那个绝对路径，例如，通过JVM系统属性“${…}”占位符在运行时加载。

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// create and configure beans
ApplicationContext context =
    new ClassPathXmlApplicationContext(new String[] {"services.xml", "daos.xml"});

// retrieve configured instance
PetStoreService service = context.getBean("petStore", PetStoreService.class);

// use configured instance
List<String> userList = service.getUsernameList();

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

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

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1.典型地，容器直接通过反射调用bean的构造方法来创建一个bean，这个Java代码中使用new操作符是等价的。
2.容器通过调用工厂类中的static工厂方法来创建一个bean。通过调用static工厂方法返回的对象类型可能是同一个类，也可能是完全不同的另一个类。 
内部类名字。如果为一个static嵌套类配置bean定义，必须使用嵌套类的二进制名字。 
例如，如果在com.example包中有一个类叫Foo，并且Foo类中有一个static嵌套类叫Bar，那么bean定义中的class属性的值应该是com.example.Foo$Bar。 
注意使用$字符分割嵌套类和外部类。

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

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

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

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

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

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<!-- 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"/>

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public class DefaultServiceLocator {

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

    public ClientService createClientServiceInstance() {
        return clientService;
    }
}

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<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"/>

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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;
    }

}

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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...
}

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package x.y;

public class Foo {

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

}

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<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>

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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;
    }

}

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

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

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

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package examples;

public class ExampleBean {

    // Fields omitted

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

}

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public class SimpleMovieLister {

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

    // a setter method so that the Spring container can inject a MovieFinder
    public void setMovieFinder(MovieFinder movieFinder) {
        this.movieFinder = movieFinder;
    }

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

}

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基于构造方法或基于setter方法的依赖注入？ 
因为可以混合使用基于构造方法和基于setter方法的依赖注入，所以使用构造方法注入强制依赖并使用setter方法或配置方法注入可选依赖是一个不错的原则。注意，在setter方法上使用@Required注解可以使属性变成必需的依赖。 
Spring团队一般倡导使用构造方法注入，因为它会使应用程序的组件实现为不可变的对象，并保证必需的依赖不为null。另外，构造方法注入的组件总是以完全初始化的状态返回给客户端(调用)代码。注意，大量的构造方法参数是代码的坏味道，这意味着类可能有很多责任，应该被重构为合适的部分以实现关注点的分离。 
setter方法应该仅仅只用于可选依赖，这些可选依赖应该在类中被赋值合理的默认值。否则，在使用这项依赖的任何地方都要做非null检查。setter方法注入的好处之一是可以使那个类的对象稍后重新配置或重新注入。使用JMX MBeans的管理是使用setter注入很好的案例。 
特定的类选择最合适的依赖注入方式。有时你并没有第三方类的源码，你就需要选择使用哪种方式。例如，如果一个第三方类没有暴露任何setter方法，那么只能选择构造方法注入了。

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·ApplicationContext被创建并初始化描述所有bean的配置元数据。配置元数据可以是XML、Java代码或注解。
·对于每一个bean，它的依赖以属性、构造方法参数或静态工厂方法参数的形式表示。这些依赖在bean实际创建时被提供给它。
·每一个属性或构造方法参数都是将被设置的值的实际定义，或容器中另一个bean的引用。
·每一个值类型的属性或构造方法参数都会从特定的形式转化为它的实际类型。默认地，Spring可以把字符串形式的值转化为所有的内置类型，比如int, long, String, boolean，等等。

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循环依赖 
如果你主要使用构造方法注入，很有可能创建一个无法解决的循环依赖场景。 
例如，类A使用构造方法注入时需要类B的一个实例，类B使用构造方法注入时需要类A的一个实例。如果为类A和B配置bean互相注入，Spring IoC容器会在运行时检测出循环引用，并抛出异常BeanCurrentlyInCreationException。 
一种解决方法是把一些类配置为使用setter方法注入而不是构造方法注入。作为替代方案，避免构造方法注入，而只使用setter方法注入。换句话说，尽管不推荐，但是可以通过setter方法注入配置循环依赖。 
不像典型的案例（没有循环依赖），A和B之间的循环依赖使得一个bean在它本身完全初始化之前被注入了另一个bean（经典的先有鸡/先有蛋问题）。

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<bean id="exampleBean" class="examples.ExampleBean">
    <!-- setter injection using the nested ref element -->
    <property name="beanOne">
        <ref bean="anotherExampleBean"/>
    </property>

    <!-- setter injection using the neater ref attribute -->
    <property name="beanTwo" ref="yetAnotherBean"/>
    <property name="integerProperty" value="1"/>
</bean>

<bean id="anotherExampleBean" class="examples.AnotherBean"/>
<bean id="yetAnotherBean" class="examples.YetAnotherBean"/>

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public class ExampleBean {

    private AnotherBean beanOne;
    private YetAnotherBean beanTwo;
    private int i;

    public void setBeanOne(AnotherBean beanOne) {
        this.beanOne = beanOne;
    }

    public void setBeanTwo(YetAnotherBean beanTwo) {
        this.beanTwo = beanTwo;
    }

    public void setIntegerProperty(int i) {
        this.i = i;
    }

}

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<bean id="exampleBean" class="examples.ExampleBean">
    <!-- constructor injection using the nested ref element -->
    <constructor-arg>
        <ref bean="anotherExampleBean"/>
    </constructor-arg>

    <!-- constructor injection using the neater ref attribute -->
    <constructor-arg ref="yetAnotherBean"/>

    <constructor-arg type="int" value="1"/>
</bean>

<bean id="anotherExampleBean" class="examples.AnotherBean"/>
<bean id="yetAnotherBean" class="examples.YetAnotherBean"/>

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public class ExampleBean {

    private AnotherBean beanOne;
    private YetAnotherBean beanTwo;
    private int i;

    public ExampleBean(
        AnotherBean anotherBean, YetAnotherBean yetAnotherBean, int i) {
        this.beanOne = anotherBean;
        this.beanTwo = yetAnotherBean;
        this.i = i;
    }

}

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<bean id="exampleBean" class="examples.ExampleBean" factory-method="createInstance">
    <constructor-arg ref="anotherExampleBean"/>
    <constructor-arg ref="yetAnotherBean"/>
    <constructor-arg value="1"/>
</bean>

<bean id="anotherExampleBean" class="examples.AnotherBean"/>
<bean id="yetAnotherBean" class="examples.YetAnotherBean"/>

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public class ExampleBean {

    // a private constructor
    private ExampleBean(...) {
        ...
    }

    // a static factory method; the arguments to this method can be
    // considered the dependencies of the bean that is returned,
    // regardless of how those arguments are actually used.
    public static ExampleBean createInstance (
        AnotherBean anotherBean, YetAnotherBean yetAnotherBean, int i) {

        ExampleBean eb = new ExampleBean (...);
        // some other operations...
        return eb;
    }

}

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<bean id="myDataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close">
    <!-- results in a setDriverClassName(String) call -->
    <property name="driverClassName" value="com.mysql.jdbc.Driver"/>
    <property name="url" value="jdbc:mysql://localhost:3306/mydb"/>
    <property name="username" value="root"/>
    <property name="password" value="masterkaoli"/>
</bean>

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<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:p="http://www.springframework.org/schema/p"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="myDataSource" class="org.apache.commons.dbcp.BasicDataSource"
        destroy-method="close"
        p:driverClassName="com.mysql.jdbc.Driver"
        p:url="jdbc:mysql://localhost:3306/mydb"
        p:username="root"
        p:password="masterkaoli"/>

</beans>

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<bean id="mappings"
    class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">

    <!-- typed as a java.util.Properties -->
    <property name="properties">
        <value>
            jdbc.driver.className=com.mysql.jdbc.Driver
            jdbc.url=jdbc:mysql://localhost:3306/mydb
        </value>
    </property>
</bean>

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<bean id="theTargetBean" class="..."/>

<bean id="theClientBean" class="...">
    <property name="targetName">
        <idref bean="theTargetBean" />
    </property>
</bean>

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<bean id="theTargetBean" class="..." />

<bean id="client" class="...">
    <property name="targetName" value="theTargetBean" />
</bean>

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idref元素的local属性在4.0版本的xsd中不再支持了，因为它不提供对普通bean的引用。在升级的4.0的schema时只要把已存在的idref local改成idref bean即可。

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<ref bean="someBean"/>

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<!-- in the parent context -->
<bean id="accountService" class="com.foo.SimpleAccountService">
    <!-- insert dependencies as required as here -->
</bean>

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<!-- in the child (descendant) context -->
<bean id="accountService" <!-- bean name is the same as the parent bean -->
    class="org.springframework.aop.framework.ProxyFactoryBean">
    <property name="target">
        <ref parent="accountService"/> <!-- notice how we refer to the parent bean -->
    </property>
    <!-- insert other configuration and dependencies as required here -->
</bean>

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ref元素的local属性在4.0版本的xsd中不再支持了，因为它不提供对普通bean的引用。在升级的4.0的schema时只要把已存在的ref local改成ref bean即可。（译者注：ref local只能引用同一个文件中的bean，所以不建议使用了，改成ref bean即可。）

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<bean id="outer" class="...">
    <!-- instead of using a reference to a target bean, simply define the target bean inline -->
    <property name="target">
        <bean class="com.example.Person"> <!-- this is the inner bean -->
            <property name="name" value="Fiona Apple"/>
            <property name="age" value="25"/>
        </bean>
    </property>
</bean>

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<bean id="moreComplexObject" class="example.ComplexObject">
    <!-- results in a setAdminEmails(java.util.Properties) call -->
    <property name="adminEmails">
        <props>
            <prop key="administrator">administrator@example.org</prop>
            <prop key="support">support@example.org</prop>
            <prop key="development">development@example.org</prop>
        </props>
    </property>
    <!-- results in a setSomeList(java.util.List) call -->
    <property name="someList">
        <list>
            <value>a list element followed by a reference</value>
            <ref bean="myDataSource" />
        </list>
    </property>
    <!-- results in a setSomeMap(java.util.Map) call -->
    <property name="someMap">
        <map>
            <entry key="an entry" value="just some string"/>
            <entry key ="a ref" value-ref="myDataSource"/>
        </map>
    </property>
    <!-- results in a setSomeSet(java.util.Set) call -->
    <property name="someSet">
        <set>
            <value>just some string</value>
            <ref bean="myDataSource" />
        </set>
    </property>
</bean>

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<beans>
    <bean id="parent" abstract="true" class="example.ComplexObject">
        <property name="adminEmails">
            <props>
                <prop key="administrator">administrator@example.com</prop>
                <prop key="support">support@example.com</prop>
            </props>
        </property>
    </bean>
    <bean id="child" parent="parent">
        <property name="adminEmails">
            <!-- the merge is specified on the child collection definition -->
            <props merge="true">
                <prop key="sales">sales@example.com</prop>
                <prop key="support">support@example.co.uk</prop>
            </props>
        </property>
    </bean>
<beans>

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public class Foo {

    private Map<String, Float> accounts;

    public void setAccounts(Map<String, Float> accounts) {
        this.accounts = accounts;
    }
}

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<beans>
    <bean id="foo" class="x.y.Foo">
        <property name="accounts">
            <map>
                <entry key="one" value="9.99"/>
                <entry key="two" value="2.75"/>
                <entry key="six" value="3.99"/>
            </map>
        </property>
    </bean>
</beans>

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<bean class="ExampleBean">
    <property name="email" value=""/>
</bean>

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exampleBean.setEmail("")

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<bean class="ExampleBean">
    <property name="email">
        <null/>
    </property>
</bean>

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exampleBean.setEmail(null)

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<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:p="http://www.springframework.org/schema/p"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean name="classic" class="com.example.ExampleBean">
        <property name="email" value="foo@bar.com"/>
    </bean>

    <bean name="p-namespace" class="com.example.ExampleBean"
        p:email="foo@bar.com"/>
</beans>

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<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:p="http://www.springframework.org/schema/p"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean name="john-classic" class="com.example.Person">
        <property name="name" value="John Doe"/>
        <property name="spouse" ref="jane"/>
    </bean>

    <bean name="john-modern"
        class="com.example.Person"
        p:name="John Doe"
        p:spouse-ref="jane"/>

    <bean name="jane" class="com.example.Person">
        <property name="name" value="Jane Doe"/>
    </bean>
</beans>

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<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:c="http://www.springframework.org/schema/c"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd">

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

    <!-- traditional declaration -->
    <bean id="foo" class="x.y.Foo">
        <constructor-arg ref="bar"/>
        <constructor-arg ref="baz"/>
        <constructor-arg value="foo@bar.com"/>
    </bean>

    <!-- c-namespace declaration -->
    <bean id="foo" class="x.y.Foo" c:bar-ref="bar" c:baz-ref="baz" c:email="foo@bar.com"/>

</beans>

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<!-- c-namespace index declaration -->
<bean id="foo" class="x.y.Foo" c:_0-ref="bar" c:_1-ref="baz"/>

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由于XML语法，索引符号需要以 _ 开头作为XML属性名，而不能以数字开头（即使在一些IDE中允许）。

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<bean id="foo" class="foo.Bar">
    <property name="fred.bob.sammy" value="123" />
</bean>

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<bean id="beanOne" class="ExampleBean" depends-on="manager"/>
<bean id="manager" class="ManagerBean" />

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<bean id="beanOne" class="ExampleBean" depends-on="manager,accountDao">
    <property name="manager" ref="manager" />
</bean>

<bean id="manager" class="ManagerBean" />
<bean id="accountDao" class="x.y.jdbc.JdbcAccountDao" />

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depends-on属性能够同时指定初始化时依赖和通信销毁时依赖，这只能运用在单例bean的情况中。依赖的bean在给定的bean销毁之前被销毁。因此，depends-on也能够控制关闭的顺序。初始化的时候依赖的对象先初始化才能注入，销毁时需要依赖的对象先销毁才能解绑。

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<bean id="lazy" class="com.foo.ExpensiveToCreateBean" lazy-init="true"/>
<bean name="not.lazy" class="com.foo.AnotherBean"/>

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<beans default-lazy-init="true">
    <!-- no beans will be pre-instantiated... -->
</beans>

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·自动装配将极大地减少指定属性或构造方法参数的需要（在这点上，其它机制比如本章其它小节讲解的bean模板也是有价值的）。
·自动装配可以更新配置当你的对象进化时。例如，如果你需要为一个类添加一个依赖，那么不需要修改配置就可以自动满足。因此，自动装配在开发期间非常有用，但不否定在代码库变得更稳定的时候切换到显式的装配。

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·在property和constructor-arg上显式设置的依赖总是覆盖自动装配。而且，不能自动装配所谓的简单属性，如基本类型、String和Classes（也包括简单属性的数组）。这是设计层面的局限性。
·自动装配没有显式装配精确。如上表所述，尽管Spring很小心地避免了模棱两可的猜测，但其管理的对象之间的关系并不会被明确地记录。
·从Spring容器生成文档的工具可能找不到装配信息。
·容器中的多个bean定义可能会匹配setter方法或构造方法参数指定的类型。对于数组、集合或Map，这未必是个问题。但是，对于那些需要单个值的依赖，这种歧义并不能随意解决。如果没有各自不同的bean定义，将会抛出异常。

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·放弃自动装配，改为显式地装配。
·设置bean的autowire-candidate属性为false以避免自动装配，这会在下一章节讲解。
·设置<bean/>标签的primary属性为true，从而为其指定一个单独的bean作为主要的候选者。
·使用基于注解的配置实现更细粒度的控制，参考6.9 基于注解的容器配置。

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// a class that uses a stateful Command-style class to perform some processing
package fiona.apple;

// Spring-API imports
import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;

public class CommandManager implements ApplicationContextAware {

    private ApplicationContext applicationContext;

    public Object process(Map commandState) {
        // grab a new instance of the appropriate Command
        Command command = createCommand();
        // set the state on the (hopefully brand new) Command instance
        command.setState(commandState);
        return command.execute();
    }

    protected Command createCommand() {
        // notice the Spring API dependency!
        return this.applicationContext.getBean("command", Command.class);
    }

    public void setApplicationContext(
            ApplicationContext applicationContext) throws BeansException {
        this.applicationContext = applicationContext;
    }
}

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·为了能使动态的子类有效，被继承的类不能是final，且被重写的方法也不能是final。
·单元测试一个具有抽象方法的类时，需要手动继承此类并重写其抽象方法。
·组件扫描的具体方法也需要具体类。
·一项关键限制是查找方法不能使用工厂方法和配置类中的@Bean方法，因为容器不会在运行时创建一个子类及其实例。
·最后，方法注入的目标对象不能被序列化。

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package fiona.apple;

// no more Spring imports!

public abstract class CommandManager {

    public Object process(Object commandState) {
        // grab a new instance of the appropriate Command interface
        Command command = createCommand();
        // set the state on the (hopefully brand new) Command instance
        command.setState(commandState);
        return command.execute();
    }

    // okay... but where is the implementation of this method?
    protected abstract Command createCommand();
}

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<public|protected> [abstract] <return-type> theMethodName(no-arguments);

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<!-- a stateful bean deployed as a prototype (non-singleton) -->
<bean id="command" class="fiona.apple.AsyncCommand" scope="prototype">
    <!-- inject dependencies here as required -->
</bean>

<!-- commandProcessor uses statefulCommandHelper -->
<bean id="commandManager" class="fiona.apple.CommandManager">
    <lookup-method name="createCommand" bean="command"/>
</bean>

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有兴趣的读者可能会发现ServiceLocatorFactoryBean（位于包org.springframework.beans.factory.config中）就是这么用的。ServiceLocatorFactoryBean中用法与其它工具类一样，ObjectFactoryCreatingFactoryBean，但是它允许你使用自己的查找接口而不是spring指定的查找接口。请参考附加信息中这些类的javadoc文档。

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public class MyValueCalculator {

    public String computeValue(String input) {
        // some real code...
    }

    // some other methods...

}

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/**
 * meant to be used to override the existing computeValue(String)
 * implementation in MyValueCalculator
 */
public class ReplacementComputeValue implements MethodReplacer {

    public Object reimplement(Object o, Method m, Object[] args) throws Throwable {
        // get the input value, work with it, and return a computed result
        String input = (String) args[0];
        ...
        return ...;
    }
}

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<bean id="myValueCalculator" class="x.y.z.MyValueCalculator">
    <!-- arbitrary method replacement -->
    <replaced-method name="computeValue" replacer="replacementComputeValue">
        <arg-type>String</arg-type>
    </replaced-method>
</bean>

<bean id="replacementComputeValue" class="a.b.c.ReplacementComputeValue"/>

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java.lang.String
String
Str