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。