Spring后置处理器

Spring后置处理器(BeanPostProcessor)

后置处理器的作用

1. Spring Bean生命周期中会调用BeanPostProcessor接口，即为后置处理器，通过改接口可以自定义调用初始化前后执行的操作方法。

2. 接口中包含两个方法：

   • postProcessBeforeInitialization() ：在 Bean 实例化、属性注入后，初始化前调用。

   • postProcessAfterInitialization() ：在 Bean 实例化、属性注入、初始化完成后调用。

   注意:postProcessBeforeInitialization 和 postProcessAfterInitialization 方法返回值不能为 null，否则会报空指针异常或者通过 getBean() 方法获取不到 Bean 实例对象。

3. 多个后置处理器的调用顺序： 添加多个后置处理器实现类时，默认情况下 Spring 容器会根据后置处理器的定义顺序来依次调用。也可以通过实现 Ordered 接口的 getOrder 方法指定后置处理器的执行顺序。该方法返回值为整数，默认值为 0，取值越大优先级越低。

代码示例

1. Java类

    package org.example;
    ​
    public class HelloWorld {
        private String message;
    ​
        public void init(){
            System.out.println("Bean正在初始化");
        }
    ​
        public void destroy(){
            System.out.println("Bean将要被销毁");
        }
    ​
    ​
        public String getMessage() {
            return message;
        }
    ​
        public void setMessage(String message) {
            this.message = message;
        }
    }
    ​

   
   

2. 后置处理器类1

    package org.example;
    ​
    import org.springframework.beans.BeansException;
    import org.springframework.beans.factory.config.BeanPostProcessor;
    import org.springframework.core.Ordered;
    ​
    public class InitHelloWorld implements BeanPostProcessor, Ordered {
    ​
        @Override
        public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
            System.out.println("A Before:"+beanName);
            return bean;
        }
    ​
        @Override
        public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
            System.out.println("A After:"+beanName);
            return bean;
        }
    ​
        @Override
        public int getOrder() {
            return 5;
        }
    }
    ​

   
   

3. 后置处理器类2

    package org.example;
    ​
    import org.springframework.beans.BeansException;
    import org.springframework.beans.factory.config.BeanPostProcessor;
    import org.springframework.core.Ordered;
    ​
    public class InitHelloWorld2 implements BeanPostProcessor, Ordered {
    ​
    ​
        @Override
        public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
            System.out.println("B Before : " + beanName);
            return bean;
        }
    ​
        @Override
        public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
            System.out.println("B After : " + beanName);
            return bean;
        }
    ​
        @Override
        public int getOrder() {
            return 0;
        }
    }
    ​

   
   

4. XML配置文件

    <?xml version="1.0" encoding="UTF-8"?>
    <beans xmlns="http://www.springframework.org/schema/beans"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xsi:schemaLocation="http://www.springframework.org/schema/beans
           http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">
    ​
        <bean id="hello" class="org.example.HelloWorld" init-method="init" destroy-method="destroy">
            <property name="message" value="Hello World"/>
        </bean>
    ​
        <!--注册处理器-->
        <bean class="org.example.InitHelloWorld"/>
        <bean class="org.example.InitHelloWorld2"/>
    ​
    ​
    ​
    </beans>

   
   

5. Main方法

    package org.example;
    ​
    import org.springframework.context.support.AbstractApplicationContext;
    import org.springframework.context.support.ClassPathXmlApplicationContext;
    ​
    ​
    public class App {
        public static void main( String[] args ) {
            //创建bean工厂 使用ApplicationContext的子类AbstractApplicationContext
            AbstractApplicationContext context=new ClassPathXmlApplicationContext("Beans.xml");
    ​
            HelloWorld obj=(HelloWorld)context.getBean("hello");
            System.out.println(obj.getMessage());
            //在非web应用中关闭IoC容器
            context.registerShutdownHook();
        }
    }
    ​

   
   

6. 运行结果

    B Before : hello
    A Before:hello
    Bean正在初始化
    B After : hello
    A After:hello
    Hello World
    17:20:01.919 [SpringContextShutdownHook] DEBUG org.springframework.context.support.ClassPathXmlApplicationContext - Closing org.springframework.context.support.ClassPathXmlApplicationContext@4cf4d528, started on Wed Mar 30 17:20:01 CST 2022
    Bean将要被销毁