Spring中的后置处理器BeanPostProcessor详解
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 { //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; //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
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; } }
Test case:
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
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