BeanFactoryPostProcessor和BeanPostProcessor

BeanFactoryPostProcessor和BeanPostProcessor，这两个接口，都是Spring初始化bean时对外暴露的扩展点。两个接口名称看起来很相似，但作用及使用场景却不同，分析如下：

1、BeanFactoryPostProcessor接口

该接口的定义如下：

public interface BeanFactoryPostProcessor {

/**
 * Modify the application context's internal bean factory after its standard
 * initialization. All bean definitions will have been loaded, but no beans
 * will have been instantiated yet. This allows for overriding or adding
 * properties even to eager-initializing beans.
 * @param beanFactory the bean factory used by the application context
 * @throws org.springframework.beans.BeansException in case of errors
 */
void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException;

} 实现该接口，可以在spring的bean创建之前，修改bean的定义属性。也就是说，Spring允许BeanFactoryPostProcessor在容器实例化任何其它bean之前读取配置元数据，并可以根据需要进行修改，例如可以把bean的scope从singleton改为prototype，也可以把property的值给修改掉。可以同时配置多个BeanFactoryPostProcessor，并通过设置'order'属性来控制各个BeanFactoryPostProcessor的执行次序。

注意：BeanFactoryPostProcessor是在spring容器加载了bean的定义文件之后，在bean实例化之前执行的。接口方法的入参是ConfigurrableListableBeanFactory，使用该参数，可以获取到相关bean的定义信息。

2、BeanPostProcessor接口

该接口的定义如下：

public interface BeanPostProcessor {

/**
 * Apply this BeanPostProcessor to the given new bean instance <i>before</i> any bean
 * initialization callbacks (like InitializingBean's <code>afterPropertiesSet</code>
 * or a custom init-method). The bean will already be populated with property values.
 * The returned bean instance may be a wrapper around the original.
 * @param bean the new bean instance
 * @param beanName the name of the bean
 * @return the bean instance to use, either the original or a wrapped one
 * @throws org.springframework.beans.BeansException in case of errors
 * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
 */
Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException;

/**
 * Apply this BeanPostProcessor to the given new bean instance <i>after</i> any bean
 * initialization callbacks (like InitializingBean's <code>afterPropertiesSet</code>
 * or a custom init-method). The bean will already be populated with property values.
 * The returned bean instance may be a wrapper around the original.
 * <p>In case of a FactoryBean, this callback will be invoked for both the FactoryBean
 * instance and the objects created by the FactoryBean (as of Spring 2.0). The
 * post-processor can decide whether to apply to either the FactoryBean or created
 * objects or both through corresponding <code>bean instanceof FactoryBean</code> checks.
 * <p>This callback will also be invoked after a short-circuiting triggered by a
 * {@link InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation} method,
 * in contrast to all other BeanPostProcessor callbacks.
 * @param bean the new bean instance
 * @param beanName the name of the bean
 * @return the bean instance to use, either the original or a wrapped one
 * @throws org.springframework.beans.BeansException in case of errors
 * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
 * @see org.springframework.beans.factory.FactoryBean
 */
Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException;

} BeanPostProcessor，可以在spring容器实例化bean之后，在执行bean的初始化方法前后，添加一些自己的处理逻辑。这里说的初始化方法，指的是下面两种：

1）bean实现了InitializingBean接口，对应的方法为afterPropertiesSet

2）在bean定义的时候，通过init-method设置的方法

注意：BeanPostProcessor是在spring容器加载了bean的定义文件并且实例化bean之后执行的。BeanPostProcessor的执行顺序是在BeanFactoryPostProcessor之后。

3、实战

BeanFactoryPostProcessor

public class MyBeanFactoryPostProcessor implements BeanFactoryPostProcessor {

    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        System.out.println("1. 调用BeanFactoryPostProcessor的postProcessBeanFactory");
        BeanDefinition bd = beanFactory.getBeanDefinition("myJavaBean");
        MutablePropertyValues pv = bd.getPropertyValues();
        pv.addPropertyValue("remark", "BeanFactoryPostProcessor中修改之后的remark");
    }
}

BeanPostProcessor

public class MyBeanPostProcessor implements BeanPostProcessor {

    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        if ("myJavaBean".equals(beanName)){
            System.out.println("3. 调用BeanPostProcessor.postProcessBeforeInitialization");
        }
        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        if ("myJavaBean".equals(beanName)){
            System.out.println("7. 调用BeanPostProcessor.postProcessAfterInitialization");
        }
        return bean;
    }
}

配置类

@Configuration
public class MyConfig {
    @Bean(initMethod = "initMethod", destroyMethod = "destroyMethod")
    public MyJavaBean myJavaBean() {
        MyJavaBean bean = new MyJavaBean();
        bean.setRemark("原始remark");
        return bean;
    }

    @Bean
    public MyBeanFactoryPostProcessor myBeanFactoryPostProcessor(){
        return new MyBeanFactoryPostProcessor();
    }

    @Bean
    public MyBeanPostProcessor myBeanPostProcessor(){
        return new MyBeanPostProcessor();
    }
}

Bean

public class MyJavaBean implements InitializingBean, DisposableBean {
    private String desc;
    private String remark;

    public MyJavaBean() {
        System.out.println("2 Bean的无参构造函数");
    }

    public MyJavaBean(String desc, String remark) {
        this.desc = desc;
        this.remark = remark;
        System.out.println("2 Bean的全参构造函数");
    }

    @PostConstruct
    public void postConstruct() {
        System.out.println("4. 调用PostConstruct方法");
    }


    public String getDesc() {
        return desc;
    }


    public void setDesc(String desc) {
        System.out.println("调用setDesc方法");
        this.desc = desc;
    }

    public String getRemark() {
        return remark;
    }

    public void setRemark(String remark) {
        System.out.println("调用setRemark方法");
        this.remark = remark;
        System.out.println("remark = " + this.remark);
    }

    @Override
    public void afterPropertiesSet() throws Exception {
        System.out.println("5. 调用InitializingBean.afterPropertiesSet方法");
        this.desc = "afterPropertiesSet中修改之后的desc";
    }

    public void initMethod() {
        System.out.println("6. 调用Bean的init方法");
    }


    @Override
    public void destroy() throws Exception {
        System.out.println("8. 调用DisposableBean.destroy");
    }

    public void destroyMethod() {
        System.out.println("9. 调用Bean的destroy方法");
    }

    @Override
    public String toString() {
        StringBuilder builder = new StringBuilder();
        builder.append("[desc：").append(desc);
        builder.append("， remark：").append(remark).append("]");
        return builder.toString();
    }
}

启动类

@SpringBootApplication
public class PostProcessorApplication {


    public static void main(String[] args) {
        ApplicationContext applicationContext = SpringApplication.run(PostProcessorApplication.class, args);
        MyJavaBean bean = (MyJavaBean) applicationContext.getBean("myJavaBean");
        System.out.println("=======================结果====================");
        System.out.println("desc：" + bean.getDesc());
        System.out.println("remark：" + bean.getRemark());
        System.out.println("======================结果====================");

    }

}

执行顺序：

1. 调用BeanFactoryPostProcessor的postProcessBeanFactory
2 Bean的无参构造函数
调用setRemark方法
remark = 原始remark
调用setRemark方法
remark = BeanFactoryPostProcessor中修改之后的remark
******beanName = myJavaBean
******beanFactory = org.springframework.beans.factory.support.DefaultListableBeanFactory
******applicationContext = org.springframework.context.annotation.AnnotationConfigApplicationContext
3. 调用BeanPostProcessor.postProcessBeforeInitialization
4. 调用PostConstruct方法
5. 调用InitializingBean.afterPropertiesSet方法
6. 调用Bean的init方法
7. 调用BeanPostProcessor.postProcessAfterInitialization
=======================结果====================
desc：afterPropertiesSet中修改之后的desc
remark：BeanFactoryPostProcessor中修改之后的remark
======================结果====================
8. 调用DisposableBean.destroy
9. 调用Bean的destroy方法

BeanFactoryPostProcessor对Bean属性的修改延迟到了Bean初始化完成之后才执行

4、进一步深入分析

在使用ApplicationContext启动spring容器的时候，在AbstractApplicationContext.refresh()方法中，完成相关初始化工作：

img

1）BeanFactoryPostProcessor.postProcessBeanFactory，是在第5步执行的

2）而BeanPostProcessor的执行，取决于配置文件中bean的定义，如果定义的bean是singleton并且不是抽象类，也不延迟初始化，则BeanPostProcessor是在第11步中执行；而对于prototype的bean，BeanPostProcessor是在程序getBean的时候执行的。在第6步中，调用registerBeanPostProcessors方法，注册所有实现BeanPostProcessor接口的bean

5、总结

1、创建（调用构造函数） 2、set属性（set方法注入属性） 3、判断是否实现BeanNameAware接口，并调用接口的setBeanName方法 4、判断是否实现BeanFactoryAware接口，并调用接口的setBeanFactory方法 5、判断是否实现ApplicationContextAware接口，并调用接口的setApplicationContext方法 6、判断是否实现BeanPostProcessor接口，并调用接口的postProcessBeforeInitialization方法 7、判断是否实现InitializingBean接口，并调用接口的afterPropertiesSet方法 8、判断是否自定义init方法，并调用 9、判断是否实现BeanPostProcessor接口（同6），并调用接口的postProcessAfterInitialization方法 10、业务代码中Bean对象的使用 11、当容器销毁时，判断是否实现DisposableBean接口，并调用接口的destroy方法 12、判断是否自定义销毁方法，并调用

对于 BeanNameAware BeanFactoryAware ApplicationContextAware 这3个接口我们平时很少实现它，一般用于让Bean能够感知到BeanName BeanFactory ApplicationContext

public class MyJavaBean implements BeanNameAware, BeanFactoryAware, ApplicationContextAware {

    private String beanName;
    private BeanFactory beanFactory;
    private ApplicationContext applicationContext;


    @Override
    public void setBeanName(String s) {
        this.beanName = s;
        System.out.println("******beanName = " + this.beanName);
    }

    @Override
    public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
        this.beanFactory = beanFactory;
        System.out.println("******beanFactory = " + this.beanFactory);

    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        this.applicationContext = applicationContext;
        System.out.println("******applicationContext = " + this.applicationContext);
    }
}

参考

Spring的BeanFactoryPostProcessor和BeanPostProcessor

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