Spring中的后置处理器BeanPostProcessor讲解

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http://www.cnblogs.com/sishang/p/6576665.html

BeanPostProcessor接口作用：

如果我们想在Spring容器中完成bean实例化、配置以及其他初始化方法前后要添加一些自己逻辑处理。我们需要定义一个或多个BeanPostProcessor接口实现类，然后注册到Spring IoC容器中。

package com.test.spring;import org.springframework.beans.BeansException;import org.springframework.beans.factory.config.BeanPostProcessor;/** * bean后置处理器 * @author zss * */public class PostProcessor implements BeanPostProcessor {    @Override    public Object postProcessBeforeInitialization(Object bean,            String beanName) throws BeansException {        if ("narCodeService".equals(beanName)) {//过滤掉bean实例ID为narCodeService            return bean;        }        System.out.println("后置处理器处理bean=【"+beanName+"】开始");        try {            Thread.sleep(1000);        } catch (InterruptedException e) {            e.printStackTrace();        }        return bean;    }    @Override    public Object postProcessAfterInitialization(Object bean,            String beanName) throws BeansException {        if ("narCodeService".equals(beanName)) {            return bean;        }        System.out.println("后置处理器处理bean=【"+beanName+"】完毕!");        try {            Thread.sleep(1000);        } catch (InterruptedException e) {            e.printStackTrace();        }        return bean;    }}

注意:接口中两个方法不能返回null，如果返回null那么在后续初始化方法将报空指针异常或者通过getBean()方法获取不到bena实例对象
     因为后置处理器从Spring IoC容器中取出bean实例对象没有再次放回IoC容器中

将Spring的后置处理器PostProcessor配置到Spring配置文件中

<?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">    <!-- 定义一个bean -->     <bean id="narCodeService" class="com.test.service.impl.NarCodeServiceImpl">     </bean>    <bean id="beanLifecycle" class="com.test.spring.BeanLifecycle" init-method="init" destroy-method="close">        <property name="name" value="张三"></property>        <property name="sex" value="男"></property>    </bean>    <!-- Spring后置处理器 -->    <bean id="postProcessor" class="com.test.spring.PostProcessor"/></beans>

BeanPostProcessor API：

public interface BeanPostProcessor {        /**      * Apply this BeanPostProcessor to the given new bean instance <i>before</i> any bean      * initialization callbacks (like InitializingBean's {@code afterPropertiesSet}      * or a custom init-method). The bean will already be populated with property values.         */      //实例化、依赖注入完毕，在调用显示的初始化之前完成一些定制的初始化任务      Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException;              /**      * Apply this BeanPostProcessor to the given new bean instance <i>after</i> any bean      * initialization callbacks (like InitializingBean's {@code afterPropertiesSet}        * or a custom init-method). The bean will already be populated with property values.            */      //实例化、依赖注入、初始化完毕时执行      Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException;    }

由API可以看出:
1：后置处理器的postProcessorBeforeInitailization方法是在bean实例化，依赖注入之后及自定义初始化方法(例如：配置文件中bean标签添加init-method属性指定Java类中初始化方法、
@PostConstruct注解指定初始化方法，Java类实现InitailztingBean接口)之前调用
2：后置处理器的postProcessorAfterInitailization方法是在bean实例化、依赖注入及自定义初始化方法之后调用

注意：
   1.BeanFactory和ApplicationContext两个容器对待bean的后置处理器稍微有些不同。ApplicationContext容器会自动检测Spring配置文件中那些bean所对应的Java类实现了BeanPostProcessor
接口，并自动把它们注册为后置处理器。在创建bean过程中调用它们，所以部署一个后置处理器跟普通的bean没有什么太大区别。

2.BeanFactory容器注册bean后置处理器时必须通过代码显示的注册，在IoC容器继承体系中的ConfigurableBeanFactory接口中定义了注册方法

    /**       * Add a new BeanPostProcessor that will get applied to beans created       * by this factory. To be invoked during factory configuration.       * <p>Note: Post-processors submitted here will be applied in the order of       * registration; any ordering semantics expressed through implementing the       * {@link org.springframework.core.Ordered} interface will be ignored. Note       * that autodetected post-processors (e.g. as beans in an ApplicationContext)       * will always be applied after programmatically registered ones.       * @param beanPostProcessor the post-processor to register       */        void addBeanPostProcessor(BeanPostProcessor beanPostProcessor);

Spring如何调用多个BeanPostProcessor实现类：

我们可以在Spring配置文件中添加多个BeanPostProcessor(后置处理器)接口实现类，在默认情况下Spring容器会根据后置处理器的定义顺序来依次调用。

Spring配置文件：

<?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定义 -->        <bean id="narCodeService" class="com.test.service.impl.NarCodeServiceImpl">    </bean>    <bean id="postProcessor" class="com.test.spring.PostProcessor"/>    <bean id="postProcessorB" class="com.test.spring.PostProcessorB"/></beans>

BeanPostProcessor实现类：

package com.test.spring;import org.springframework.beans.BeansException;import org.springframework.beans.factory.config.BeanPostProcessor;/** * bean后置处理器 * @author zss * */public class PostProcessor implements BeanPostProcessor {    @Override    public Object postProcessBeforeInitialization(Object bean,            String beanName) throws BeansException {        System.out.println("后置处理器处理bean=【"+beanName+"】开始");        try {            Thread.sleep(1000);        } catch (InterruptedException e) {            e.printStackTrace();        }        return bean;    }    @Override    public Object postProcessAfterInitialization(Object bean,            String beanName) throws BeansException {        System.out.println("后置处理器处理bean=【"+beanName+"】完毕!");        try {            Thread.sleep(1000);        } catch (InterruptedException e) {            e.printStackTrace();        }        return bean;    }}----------------------------------------------------------------------------------------------------------------------------------------package com.test.spring;import org.springframework.beans.BeansException;import org.springframework.beans.factory.config.BeanPostProcessor;public class PostProcessorB implements BeanPostProcessor {    @Override    public Object postProcessBeforeInitialization(Object bean,            String beanName) throws BeansException {        System.out.println("后置处理器开始调用了");        try {            Thread.sleep(1000);        } catch (InterruptedException e) {            e.printStackTrace();        }        return bean;    }    @Override    public Object postProcessAfterInitialization(Object bean,            String beanName) throws BeansException {        System.out.println("后置处理器调用结束了");        try {            Thread.sleep(1000);        } catch (InterruptedException e) {            e.printStackTrace();        }        return bean;    }}

测试：

package com.test.spring;import org.junit.Before;import org.junit.Test;import org.springframework.context.support.AbstractApplicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext;public class T {    AbstractApplicationContext applicationcontext=null;    @Before    public void before() {        System.out.println("》》》Spring ApplicationContext容器开始初始化了......");        applicationcontext= new ClassPathXmlApplicationContext(new String[]{"test1-service.xml"});        System.out.println("》》》Spring ApplicationContext容器初始化完毕了......");    }    @Test    public void  test() {        applicationcontext.registerShutdownHook();       }}

测试结果：

》》》Spring ApplicationContext容器开始初始化了......2017-03-19 10:50:29  INFO:ClassPathXmlApplicationContext-Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@18c92ff9: startup date [Sun Mar 19 10:50:29 CST 2017]; root of context hierarchy2017-03-19 10:50:29  INFO:XmlBeanDefinitionReader-Loading XML bean definitions from class path resource [test1-service.xml]后置处理器处理bean=【narCodeService】开始后置处理器开始调用了后置处理器处理bean=【narCodeService】完毕!后置处理器调用结束了》》》Spring ApplicationContext容器初始化完毕了......2017-03-19 10:50:34  INFO:ClassPathXmlApplicationContext-Closing org.springframework.context.support.ClassPathXmlApplicationContext@18c92ff9: startup date [Sun Mar 19 10:50:29 CST 2017]; root of context hierarchy

在Spring机制中可以指定后置处理器调用顺序，通过让BeanPostProcessor接口实现类实现Ordered接口getOrder方法，该方法返回一整数， 0优先级最高，值越大优先级越低
调用顺序：优先调用继承了Ordered接口的，并按优先级顺序。之后再调用未实现Ordered接口的，按声明顺序调用。

可参考源码分析：http://blog.csdn.net/z69183787/article/details/51311749

PostProcessorRegistrationDelegate#invokeBeanFactoryPostProcessors

List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();List<String> orderedPostProcessorNames = new ArrayList<String>();List<String> nonOrderedPostProcessorNames = new ArrayList<String>();for (String ppName : postProcessorNames) {if (processedBeans.contains(ppName)) {// skip - already processed in first phase above}else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));}else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {orderedPostProcessorNames.add(ppName);}else {nonOrderedPostProcessorNames.add(ppName);}}// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.OrderComparator.sort(priorityOrderedPostProcessors);invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);// Next, invoke the BeanFactoryPostProcessors that implement Ordered.List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();for (String postProcessorName : orderedPostProcessorNames) {orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));}OrderComparator.sort(orderedPostProcessors);invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);// Finally, invoke all other BeanFactoryPostProcessors.List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();for (String postProcessorName : nonOrderedPostProcessorNames) {nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));}invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);

例如：

package com.test.spring;import org.springframework.beans.BeansException;import org.springframework.beans.factory.config.BeanPostProcessor;import org.springframework.core.Ordered;/** * bean后置处理器 * @author zss * */public class PostProcessor implements BeanPostProcessor,Ordered{    @Override    public Object postProcessBeforeInitialization(Object bean,            String beanName) throws BeansException {        System.out.println("后置处理器处理bean=【"+beanName+"】开始");        try {            Thread.sleep(1000);        } catch (InterruptedException e) {            e.printStackTrace();        }        return bean;    }    @Override    public Object postProcessAfterInitialization(Object bean,            String beanName) throws BeansException {        System.out.println("后置处理器处理bean=【"+beanName+"】完毕!");        try {            Thread.sleep(1000);        } catch (InterruptedException e) {            e.printStackTrace();        }        return bean;    }    @Override    public int getOrder() {        return 1;    }}----------------------------------------------------------------------------package com.test.spring;import org.springframework.beans.BeansException;import org.springframework.beans.factory.config.BeanPostProcessor;import org.springframework.core.Ordered;public class PostProcessorB implements BeanPostProcessor,Ordered {    @Override    public Object postProcessBeforeInitialization(Object bean,            String beanName) throws BeansException {        System.out.println("后置处理器开始调用了");        try {            Thread.sleep(1000);        } catch (InterruptedException e) {            e.printStackTrace();        }        return bean;    }    @Override    public Object postProcessAfterInitialization(Object bean,            String beanName) throws BeansException {        System.out.println("后置处理器调用结束了");        try {            Thread.sleep(1000);        } catch (InterruptedException e) {            e.printStackTrace();        }        return bean;    }    @Override    public int getOrder() {        return 0;    }}

测试结果：

》》》Spring ApplicationContext容器开始初始化了......
2017-03-19 11:04:10 INFO:ClassPathXmlApplicationContext-Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@18c92ff9: startup date [Sun Mar 19 11:04:10 CST 2017]; root of context hierarchy
2017-03-19 11:04:10 INFO:XmlBeanDefinitionReader-Loading XML bean definitions from class path resource [test1-service.xml]
后置处理器开始调用了
后置处理器处理bean=【narCodeService】开始
后置处理器调用结束了
后置处理器处理bean=【narCodeService】完毕!
》》》Spring ApplicationContext容器初始化完毕了......
2017-03-19 11:04:14 INFO:ClassPathXmlApplicationContext-Closing org.springframework.context.support.ClassPathXmlApplicationContext@18c92ff9: startup date [Sun Mar 19 11:04:10 CST 2017]; root of context hierarchy

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