Spring点滴五：Spring中的后置处理器BeanPostProcessor讲解
本文内容纲要：Spring点滴五：Spring中的后置处理器BeanPostProcessor讲解
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 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{
@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
本文内容总结：Spring点滴五：Spring中的后置处理器BeanPostProcessor讲解
原文链接：https://www.cnblogs.com/sishang/p/6576665.html
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