Spring中BeanPostProcessor和BeanFactoryPostProcessor对比
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在Spring中这两个后置处理器很有用,几乎所有的bean实例化初始化时都会用到这两个后置处理器。
首先,我们先从字眼上来区分下,BeanPostProcessor看起来像是在bean创建后进行相关的处理,BeanFactoryPostProcessor中的BeanFactory当然是用于创建bean的工厂啦,那么BeanFactoryPostProcessor应该是工厂在创建bean时进行的处理或者创建bean工厂后的处理。
下面,我们分别写两个上述接口的实现类,并配置,查看执行结果。
(1)MyBeanPostProcessor.java
package com.alan.spring.postprocessor;import org.springframework.beans.BeansException;import org.springframework.beans.factory.config.BeanPostProcessor;public class MyPostProcessor implements BeanPostProcessor{ @Override public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException { System.err.println("After Bean '" + beanName + "' created : " + bean.toString()); //这里直接改变了user的类型 if (beanName.equals("user")) { return "this is a user"; } return bean; } @Override public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException { System.err.println("Before Bean '" + beanName + "' created : " + bean.toString()); return bean; } }
(2)MyBeanFactoryPostProcessor.java
package com.alan.spring.postprocessor;import org.springframework.beans.BeansException;import org.springframework.beans.factory.config.BeanDefinition;import org.springframework.beans.factory.config.BeanFactoryPostProcessor;import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;public class MyBeanFactoryPostProcessor implements BeanFactoryPostProcessor{ @Override public void postProcessBeanFactory(ConfigurableListableBeanFactory factory) throws BeansException { BeanDefinition definition = factory.getBeanDefinition("userController"); definition.getPropertyValues().get("username"); definition.getPropertyValues().addPropertyValue("username", "tangtong"); //直接用这个方法就可以覆盖原来设置的值 } }
(3)UserController.java
说明,实际使用中是不会在controller中注入username这种有状态的属性的,因为有状态的属性就没办法使用单例了,此处仅为举例。
package com.alan.controller;import org.springframework.stereotype.Controller;@Controller("userController")public class UserController { private String username; public String getUsername() { return username; } public void setUsername(String username) { this.username = username; }}
(4)User.java
package com.alan.spring.postprocessor;public class User {}
(5)dispatcher.xml中配置上面两个后置处理器
另外,上面的controller通过扫描的方式配置了。
<bean class="com.alan.spring.postprocessor.MyPostProcessor"></bean><bean class="com.alan.spring.postprocessor.MyBeanFactoryPostProcessor"></bean><bean id="user" class="com.alan.spring.postprocessor.User"></bean>
(6)UnitTest.java
package com.alan.test;import javax.annotation.Resource;import org.junit.Test;import org.junit.runner.RunWith;import org.springframework.test.context.ContextConfiguration;import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;import com.alan.controller.UserController;@RunWith(SpringJUnit4ClassRunner.class)@ContextConfiguration(locations="classpath*:META-INF/dispatcher.xml")public class UnitTest { @Resource private UserController userController; @Resource private String user; @Test public void test() { System.err.println("MyBeanFactoryPostProcessor execute result : the controller's username property was set to : " + userController.getUsername()); System.err.println("the user is : " + user); }}
运行上面的单元测试,查看控制台的输出结果,如果不出意外,应该可以看到类似下面的字样:
Before Bean 'user' created : com.alan.spring.postprocessor.User@12bd8a64After Bean 'user' created : com.alan.spring.postprocessor.User@12bd8a64Before Bean 'userController' created : com.alan.controller.UserController@5a8ba37cAfter Bean 'userController' created : com.alan.controller.UserController@5a8ba37cMyBeanFactoryPostProcessor execute result : the controller's username property was set to : tangtongthe user is : this is a user
运行单元测试时,可以使用debug模式在两个实现类中打上断点,查看它们的执行顺序。可以发现,先执行了MyBeanFactoryPostProcessor的方法,再分别执行MyBeanPostProcessor的两个方法,且MyBeanFactoryPostProcessor只执行一次,而MyBeanPostProcessor的两个方法针对每一个bean却分别至少执行一次。
由此可见,BeanFactoryPostProcessor用于改变原来配置的bean的元数据,可以改变bean的信息,比如bean对应的类,bean引用的对象,bean属性的值等,且它的执行过程是在bean实例化之前。BeanPostProcessor则是在bean实例化之后,bean初始化前后分别执行拦截,也可以改变bean的信息,不过两者的执行时间点不同。
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