今天给大家介绍BeanPostProcessor接口用法，希望对大家能有所帮助！

1、BeanPostProcessor 概念介绍

BeanPostProcessor接口通常被称为Bean的后置处理器，它是Spring中定义的接口，可以在Spring容器的创建过程中（主要在Bean初始化前后进行工作）回调BeanPostProcessor中定义的两个方法。

2、BeanPostProcessor接口方法

postProcessBeforeInitialization：在每一个bean对象的初始化方法调用之前回调。

postProcessAfterInitialization：在每个bean对象的初始化方法调用之后被回调。

说明：以上两个方法的返回值都不能为null，否则在后续的初始化方法会报空指针或者通过getBean()方法无法获取Bean对象。主要原因是如果返回值为null的情况下以上两个方法从Spring容器获取bean实例，没有再次放入Spring容器中去，这样容器中就没有了。

2.1 BeanPostProcessor源码内容

package org.springframework.beans.factory.config;

import org.springframework.beans.BeansException;
import org.springframework.lang.Nullable;

public interface BeanPostProcessor {
    @Nullable
    default Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }

    @Nullable
    default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }
}

3、BeanPostProcessor 接口的作用

可以Spring容器中完成bean实例化、配置以及其他初始化方法前后根据业务的场景增加相应的逻辑处理。典型的案例AOP的实现。

4、代码示例

4.1 新建Person.java 类文件

package com.spring.bean;

public class Person {
    private String name;
    private Integer age;
    private String address;

    public Person(String name, Integer age, String address) {
        this.name = name;
        this.age = age;
        this.address = address;
    }

    public Person() {
    }

    public String getName() {
        return name;
    }

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

    public Integer getAge() {
        return age;
    }

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

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + ''' +
                ", age='" + age + ''' +
                ", address='" + address + ''' +
                '}';
    }
}

4.2、新建MyBeanPostProcessor.java

package com.spring.bean;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.stereotype.Component;

@Component
public class MyBeanPostProcessor implements BeanPostProcessor {
    /**
     * 实例化、依赖注入完毕，在调用显示的初始化之前完成一些自定义的初始化逻辑
     * 方法返回值不能为null
     * 返回null那么在后续初始化方法会报空指针异常或者通过getBean()方法获取不到bena实例
     * 如果设置为null情况下，后置处理器从Spring IoC容器中取出bean实例对象没有再次放回IoC容器中
     */
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("postProcessBeforeInitialization执行了"+beanName);
        return bean;
    }
    /**
     * 实例化、依赖注入、初始化完成后时执行
     * 方法返回值也不能为null
     * 如果返回null那么在后续初始化方法将报空指针异常或者通过getBean()方法获取不到bena实例对象
     *  如果设置为null情况下，后置处理器从Spring IoC容器中取出bean实例对象没有再次放回IoC容器中
     */
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("postProcessAfterInitialization"+beanName);
        return bean;
    }
}

4.3、新建TestBeanPostProcessorConfig.java 配置类

package com.spring.config;

import com.spring.bean.UserInfo;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.FilterType;
import org.springframework.stereotype.Component;
import org.springframework.stereotype.Controller;

@Configuration
@ComponentScan(value = "com.spring.bean",includeFilters = {
        @ComponentScan.Filter(type = FilterType.ANNOTATION
                , classes = {Component.class, Controller.class}
        ),
        @ComponentScan.Filter(type = FilterType.ASSIGNABLE_TYPE
                , classes = {UserInfo.class}
        ),
})
public class TestBeanPostProcessorConfig {

}

4.4、新建测试类 TestBeanPostProcessor.java

package com.spring.test;

import com.spring.config.TestBeanPostProcessorConfig;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class TestBeanPostProcessor {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext annotationContext = new AnnotationConfigApplicationContext(TestBeanPostProcessorConfig.class);

    }
}

输出结果：

postProcessBeforeInitialization执行了testBeanPostProcessorConfig
postProcessAfterInitializationtestBeanPostProcessorConfig
UserInfo构造器执行了
postProcessBeforeInitialization执行了userInfo
PostConstruct 初始化方法执行
postProcessAfterInitializationuserInfo

Process finished with exit code 0