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• BeanDefinitionRegistryPostProcessor

BeanDefinitionRegistryPostProcessor

1. 当我们用Spring来管理应用，我们会让Spring来管理所有的Bean。除了注解、Java配置和XML配置的方式来创建Bean，还有另外一种方式来创建我们的BeanDefinition。
2. 通过BeanDefinitionRegistryPostProcessor可以创建一个特别后置处理器来将BeanDefinition添加到BeanDefinitionRegistry中。它和BeanPostProcessor不同，BeanPostProcessor只是在Bean初始化的时候有个钩子让我们加入一些自定义操作；而BeanDefinitionRegistryPostProcessor可以让我们在BeanDefinition中添加一些自定义操作(对扩展开放)。

3. 源码

     public interface BeanDefinitionRegistryPostProcessor extends BeanFactoryPostProcessor {
   
        /**
         * Modify the application context's internal bean definition registry after its
         * standard initialization. All regular bean definitions will have been loaded,
         * but no beans will have been instantiated yet. This allows for adding further
         * bean definitions before the next post-processing phase kicks in.
         * @param registry the bean definition registry used by the application context
         * @throws org.springframework.beans.BeansException in case of errors
         */
        void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException;
   
    }
   

4. 案例

5. 定义bean

      public interface UserService {
          public void findByUserName(String username);
     }
   
     public class UserServiceImpl implements UserService{
         @Override
         public void findByUserName(String username) {
             System.out.println("username:"+username);
         }
     }
   

6. 自定义处理器

     自定义一个Service注册
     @Component
     public class CustomServiceRegistryPostProcessor implements BeanDefinitionRegistryPostProcessor {
   
         @Override
         public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
             RootBeanDefinition beanDefinition = new RootBeanDefinition(UserServiceImpl.class); // Service实现
             beanDefinition.setTargetType(UserService.class); // Service接口
             beanDefinition.setRole(BeanDefinition.ROLE_APPLICATION);
             registry.registerBeanDefinition("userService", beanDefinition);
         }
   
         @Override
         public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
   
         }
     }
   

7. 扫描bean

     <context:component-scan base-package="cn.jannal.spring.bean.registry" />
   

8. 测试

    @RunWith(SpringJUnit4ClassRunner.class)  
    @ContextConfiguration({"classpath:applicationContext-all.xml"})  
    public class App {


        @Autowired
        private UserService userService;

        @Test
        public void testFindByUserName(){
            userService.findByUserName("jananl");
        }
    }