BeanFactoryPostProcessor和BeanPostProcessor，这两个接口，都是Spring初始化Bean时对外暴露的扩展点。
这两个接口名称看起来相似，但作用和使用场景却不同。
BeanFactoryPostProcessor接口源码
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在容器实力话任何其他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scope从singleton改为prototype，也可以把property的值给修改掉。可以同事配置多个BeanFactoryPostProcessor，并通过设置order属性来控制各个BeanFactoryPostProcessor的执行顺序。
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
自定义BeanFactoryPostProcessor
public class MyBeanFactoryPostProcessor implements BeanFactoryPostProcessor {
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
System.out.println("调用MyBeanFactoryPostProcessor的postProcessBeanFactory");
BeanDefinition bd = beanFactory.getBeanDefinition("myJavaBean");
System.out.println("属性值============" + bd.getPropertyValues().toString());
MutablePropertyValues pv = bd.getPropertyValues();
if (pv.contains("remark")) {
pv.addPropertyValue("remark", "把备注信息修改一下");
}
bd.setScope(BeanDefinition.SCOPE_PROTOTYPE);
}
}
2、BeanPostProcessor接口源码如下
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、下面通过完整的一个例子，来加深理解
1）定义一个JavaBean
public class MyJavaBean implements InitializingBean {
private String desc;
private String remark;
public MyJavaBean() {
System.out.println("MyJavaBean的构造函数被执行啦");
}
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;
}
public void afterPropertiesSet() throws Exception {
System.out.println("调用afterPropertiesSet方法");
this.desc = "在初始化方法中修改之后的描述信息";
}
public void initMethod() {
System.out.println("调用initMethod方法");
}
public String toString() {
StringBuilder builder = new StringBuilder();
builder.append("[描述：").append(desc);
builder.append("， 备注：").append(remark).append("]");
return builder.toString();
}
}
2）定义一个BeanFactoryPostProcessor
public class MyBeanFactoryPostProcessor implements BeanFactoryPostProcessor {
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
System.out.println("调用MyBeanFactoryPostProcessor的postProcessBeanFactory");
BeanDefinition bd = beanFactory.getBeanDefinition("myJavaBean");
MutablePropertyValues pv = bd.getPropertyValues();
if (pv.contains("remark")) {
pv.addPropertyValue("remark", "在BeanFactoryPostProcessor中修改之后的备忘信息");
}
}
}
3）定义一个BeanPostProcessor
public class MyBeanPostProcessor implements BeanPostProcessor {
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
System.out.println("BeanPostProcessor，对象" + beanName + "调用初始化方法之前的数据： " + bean.toString());
return bean;
}
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
System.out.println("BeanPostProcessor，对象" + beanName + "调用初始化方法之后的数据：" + bean.toString());
return bean;
}
}
从上面的结果可以看出，BeanFactoryPostProcessor在bean实例化之前执行，之后实例化bean（调用构造函数，并调用set方法注入属性值），然后在调用两个初始化方法前后，执行了BeanPostProcessor