Spring BeanPostProcessor接口使用详解

Spring中提供了很多PostProcessor供开发者进行拓展，例如：BeanPostProcessor、BeanFactoryPostProcessor、BeanValidationPostProcessor等一系列后处理器。他们的使用方式大多类似，了解其中一个并掌握他的使用方式，其他的可以触类旁通。

这里以BeanPostProcessor为例展示其使用方式。

BeanPostProcessor接口提供了两个供开发者自定义的方法：postProcessBeforeInitialization、postProcessAfterInitialization。

postProcessBeforeInitialization：该方法主要针对spring在bean初始化时调用初始化方法前进行自定义处理。

postProcessAfterInitialization：该方法主要针对spring在bean初始化时调用初始化方法后进行自定义处理。

示例代码：

/**
 * 测试bean
 */
public class Cat {
  private String name;
  private int age;
  public void say() {
    System.out.println("name:" + name);
    System.out.println("age:" + age);
  }

  public String getName() {
    return name;
  }

  public void setName(String name) {
    this.name = name;
  }

  public int getAge() {
    return age;
  }

  public void setAge(int age) {
    this.age = age;
  }
}

/**
 * 自定义后处理器
 */
public class CatBeanPostProcessor implements BeanPostProcessor {

  @Nullable
  @Override
  public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
    if (bean instanceof Cat) {
      //输出原始属性
      Cat cat = (Cat) bean;
      cat.say();
      return bean;
    }
    return bean;
  }

  @Nullable
  @Override
  public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
    if (bean instanceof Cat) {
      //修改属性值，并返回
      Cat cat = (Cat) bean;
      cat.setName("hello maomi");
      cat.setAge(3);
      return cat;
    }
    return bean;
  }
}

/**
 * 运行
 */
public class Run {
  public static void main(String[] args) {
    ApplicationContext applicationContext = new ClassPathXmlApplicationContext("spring-bean.xml");
    Cat cat = (Cat) applicationContext.getBean("cat");
    cat.say();
  }
}

xml配置信息

  <!--配置bean并初始化-->
  <bean id="cat" class="com.source.postprocessor.Cat" >
    <property name="name" value="HelloKitty" />
    <property name="age" value="1" />
  </bean>

  <bean id="catBeanPostProcessor" class="com.source.postprocessor.CatBeanPostProcessor" />

输出结果：

name:HelloKitty
age:1
name:hello maomi
age:3

可以看到通过后处理器处理过后的bean信息已经改变。最后，看看源码中如何调用自定义实现的。

在初始化bean方法中：AbstractAutowireCapableBeanFactory.java

  /**
  * 初始化bean
  */
 protected Object initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd) {
   //省略部分无关代码
   Object wrappedBean = bean;
   //初始化前
   if (mbd == null || !mbd.isSynthetic()) {
     wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
   }

   try {
     //调用初始化方法初始化bean
     invokeInitMethods(beanName, wrappedBean, mbd);
   }
   catch (Throwable ex) {
     throw new BeanCreationException(
         (mbd != null ? mbd.getResourceDescription() : null),
         beanName, "Invocation of init method failed", ex);
   }
   //初始化后
   if (mbd == null || !mbd.isSynthetic()) {
     wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
   }
   return wrappedBean;
 }
 //postProcessBeforeInitialization方法调用
 @Override
 public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
     throws BeansException {

   Object result = existingBean;
   for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
     //调用自定义postProcessBeforeInitialization方法
     Object current = beanProcessor.postProcessBeforeInitialization(result, beanName);
     if (current == null) {
       return result;
     }
     result = current;
   }
   return result;
 }
 //postProcessAfterInitialization方法调用
 @Override
 public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
     throws BeansException {

   Object result = existingBean;
   for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
     //自定义postProcessAfterInitialization方法调用
     Object current = beanProcessor.postProcessAfterInitialization(result, beanName);
     if (current == null) {
       return result;
     }
     result = current;
   }
   return result;
 }

以上就是spring对自定义方法实现的调用过程。希望对大家的学习有所帮助，也希望大家多多支持我们。

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