Spring点滴五：Spring中的后置处理器BeanPostProcessor讲解

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https://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 {@Overridepublic Object postProcessBeforeInitialization(Object bean,String beanName) throws BeansException {if ("narCodeService".equals(beanName)) {//过滤掉bean实例ID为narCodeServicereturn 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;}@Overridepublic 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/beanshttp://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/beanshttp://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 {@Overridepublic 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;}@Overridepublic 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 {@Overridepublic 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;}@Overridepublic 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;@Beforepublic 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......");}@Testpublic 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 hierarchy
2017-03-19 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，默认值为 0，优先级最高，值越大优先级越低

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{@Overridepublic 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;}@Overridepublic 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;}@Overridepublic 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 {@Overridepublic 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;}@Overridepublic 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;}@Overridepublic 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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