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Spring BeanPostProcessor接口使用詳解

更新時(shí)間：2018年01月04日 11:17:09 作者：zpwd63

本篇文章主要介紹了Spring BeanPostProcessor接口使用詳解，小編覺得挺不錯(cuò)的，現(xiàn)在分享給大家，也給大家做個(gè)參考。一起跟隨小編過來看看吧

Spring中提供了很多PostProcessor供開發(fā)者進(jìn)行拓展，例如：BeanPostProcessor、BeanFactoryPostProcessor、BeanValidationPostProcessor等一系列后處理器。他們的使用方式大多類似，了解其中一個(gè)并掌握他的使用方式，其他的可以觸類旁通。

這里以BeanPostProcessor為例展示其使用方式。

BeanPostProcessor接口提供了兩個(gè)供開發(fā)者自定義的方法：postProcessBeforeInitialization、postProcessAfterInitialization。

postProcessBeforeInitialization：該方法主要針對(duì)spring在bean初始化時(shí)調(diào)用初始化方法前進(jìn)行自定義處理。

postProcessAfterInitialization：該方法主要針對(duì)spring在bean初始化時(shí)調(diào)用初始化方法后進(jìn)行自定義處理。

示例代碼：

/**
 * 測試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;
  }
}

/**
 * 自定義后處理器
 */
public class CatBeanPostProcessor implements BeanPostProcessor {

  @Nullable
  @Override
  public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
    if (bean instanceof Cat) {
      //輸出原始屬性
      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) {
      //修改屬性值，并返回
      Cat cat = (Cat) bean;
      cat.setName("hello maomi");
      cat.setAge(3);
      return cat;
    }
    return bean;
  }
}

/**
 * 運(yùn)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" />

輸出結(jié)果：

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

可以看到通過后處理器處理過后的bean信息已經(jīng)改變。最后，看看源碼中如何調(diào)用自定義實(shí)現(xiàn)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) {
   //省略部分無關(guān)代碼
   Object wrappedBean = bean;
   //初始化前
   if (mbd == null || !mbd.isSynthetic()) {
     wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
   }

   try {
     //調(diào)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方法調(diào)用
 @Override
 public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
     throws BeansException {

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

   Object result = existingBean;
   for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
     //自定義postProcessAfterInitialization方法調(diào)用
     Object current = beanProcessor.postProcessAfterInitialization(result, beanName);
     if (current == null) {
       return result;
     }
     result = current;
   }
   return result;
 }

以上就是spring對(duì)自定義方法實(shí)現(xiàn)的調(diào)用過程。希望對(duì)大家的學(xué)習(xí)有所幫助，也希望大家多多支持腳本之家。

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