Spring Bean后置处理器（BeanPostProcessor及其子接口）源码分析

其他 2020-02-25 11:19:16 阅读次数: 0

主要根据源码梳理下生命周期过程中的Bean后置处理器调用过程。包括BeanPostProcessor接口及其子接口（InstantiationAwareBeanPostProcessor、SmartInstantiationAwareBeanPostProcessor、MergedBeanDefinitionPostProcessor）的方法，贯穿整个Bean的实例化及初始化过程。

示例代码

import java.lang.reflect.Constructor;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.BeansException;
import org.springframework.beans.PropertyValues;
import org.springframework.beans.factory.config.SmartInstantiationAwareBeanPostProcessor;
import org.springframework.beans.factory.support.MergedBeanDefinitionPostProcessor;
import org.springframework.beans.factory.support.RootBeanDefinition;
import org.springframework.stereotype.Component;

@Component
public class BeanLifeCyclePostProcessor
		implements MergedBeanDefinitionPostProcessor, SmartInstantiationAwareBeanPostProcessor {

	private static final Logger _LOG = LoggerFactory.getLogger(BeanLifeCyclePostProcessor.class);
	private static final String TEST_BEAN_NAME = "newsService";

	@Override
	public void postProcessMergedBeanDefinition(RootBeanDefinition beanDefinition, Class<?> beanType, String beanName) {
		if (TEST_BEAN_NAME.equals(beanName))
			_LOG.info("=====执行MergedBeanDefinitionPostProcessor \n" + "=====的postProcessMergedBeanDefinition方法 \n"
					+ "=====缓存注解信息");

	}

	@Override
	public Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {
		if (TEST_BEAN_NAME.equals(beanName))
			_LOG.info("=====执行InstantiationAwareBeanPostProcessor \n" + "=====的postProcessBeforeInstantiation方法 \n"
					+ "=====得到bean实例前，返回代理，容器将实例化代理类");
		return SmartInstantiationAwareBeanPostProcessor.super.postProcessBeforeInstantiation(beanClass, beanName);
	}

	@Override
	public boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {

		if (TEST_BEAN_NAME.equals(beanName))
			_LOG.info("=====执行InstantiationAwareBeanPostProcessor \n" + "=====的postProcessAfterInstantiation方法 \n"
					+ "=====Bean已经实例化但spring还没有注入属性，判断Bean是否需要跳过属性填充返回True则跳过属性填充");
		return SmartInstantiationAwareBeanPostProcessor.super.postProcessAfterInstantiation(bean, beanName);
	}

	@Override
	public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
		if (TEST_BEAN_NAME.equals(beanName))
			_LOG.info("=====执行BeanPostProcessor \n" + "=====的postProcessBeforeInitialization方法 \n"
					+ "=====Bean已经实例化执行初始化方法（init-method）前可以返回指定Bean的包装实例");
		return MergedBeanDefinitionPostProcessor.super.postProcessBeforeInitialization(bean, beanName);
	}

	@Override
	public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
		if (TEST_BEAN_NAME.equals(beanName))
			_LOG.info("=====执行BeanPostProcessor \n" + "=====的postProcessAfterInitialization方法 \n"
					+ "=====Bean已经实例化执行初始化方法（init-method）后可以返回指定Bean的包装实例");
		return MergedBeanDefinitionPostProcessor.super.postProcessAfterInitialization(bean, beanName);
	}

	@Override
	public Constructor<?>[] determineCandidateConstructors(Class<?> beanClass, String beanName) throws BeansException {
		if (TEST_BEAN_NAME.equals(beanName))
			_LOG.info("=====执行SmartInstantiationAwareBeanPostProcessor \n" + "=====的determineCandidateConstructors方法 \n"
					+ "=====Bean实例化之前，推断Bean的构造方法");
		return SmartInstantiationAwareBeanPostProcessor.super.determineCandidateConstructors(beanClass, beanName);
	}

	@Override
	public Object getEarlyBeanReference(Object bean, String beanName) throws BeansException {
		if (TEST_BEAN_NAME.equals(beanName))
			_LOG.info("=====执行SmartInstantiationAwareBeanPostProcessor \n" + "=====的getEarlyBeanReference方法 \n"
					+ "=====Bean完全初始化之前，返回Bean的一个引用对象，通常用于解决循环依赖问题");
		return SmartInstantiationAwareBeanPostProcessor.super.getEarlyBeanReference(bean, beanName);
	}

	@Override
	public PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName)
			throws BeansException {
		if (TEST_BEAN_NAME.equals(beanName))
			_LOG.info("=====执行InstantiationAwareBeanPostProcessor \n" + "=====的postProcessProperties方法 \n"
					+ "=====Bean实例化后进行属性填充");
		return SmartInstantiationAwareBeanPostProcessor.super.postProcessProperties(pvs, bean, beanName);
	}
}

打印调用流程

2019-12-30 12:21:46.439  INFO 10868 --- [           main] com.qqxhb.mybatis.config.BeanLifeCyclePostProcessor   : 
=====执行InstantiationAwareBeanPostProcessor 
=====的postProcessBeforeInstantiation方法 
=====得到bean实例前，返回代理，容器将实例化代理类
2019-12-30 12:21:46.547  INFO 10868 --- [           main] com.qqxhb.mybatis.config.BeanLifeCyclePostProcessor   : 
=====执行SmartInstantiationAwareBeanPostProcessor 
=====的determineCandidateConstructors方法 
=====Bean实例化之前，推断Bean的构造方法
2019-12-30 12:21:46.548  INFO 10868 --- [           main] com.qqxhb.mybatis.config.BeanLifeCyclePostProcessor   : 
=====执行MergedBeanDefinitionPostProcessor 
=====的postProcessMergedBeanDefinition方法 
=====缓存注解信息
2019-12-30 12:21:46.548  INFO 10868 --- [           main] com.qqxhb.mybatis.config.BeanLifeCyclePostProcessor   : 
=====执行InstantiationAwareBeanPostProcessor 
=====的postProcessAfterInstantiation方法 
=====Bean已经实例化但spring还没有注入属性，判断Bean是否需要跳过属性填充返回True则跳过属性填充
2019-12-30 12:21:47.603  INFO 10868 --- [           main] com.qqxhb.mybatis.config.BeanLifeCyclePostProcessor   : 
=====执行SmartInstantiationAwareBeanPostProcessor 
=====的getEarlyBeanReference方法 
=====Bean完全初始化之前，返回Bean的一个引用对象，通常用于解决循环依赖问题
2019-12-30 12:21:47.604  INFO 10868 --- [           main] com.qqxhb.mybatis.config.BeanLifeCyclePostProcessor   : 
=====执行InstantiationAwareBeanPostProcessor 
=====的postProcessProperties方法 
=====Bean实例化后进行属性填充
2019-12-30 12:21:47.610  INFO 10868 --- [           main] com.qqxhb.mybatis.config.BeanLifeCyclePostProcessor   : 
=====执行BeanPostProcessor 
=====的postProcessBeforeInitialization方法 
=====Bean已经实例化执行初始化方法（init-method）前可以返回指定Bean的包装实例
2019-12-30 12:21:47.610  INFO 10868 --- [           main] com.qqxhb.mybatis.config.BeanLifeCyclePostProcessor   : 
=====执行BeanPostProcessor 
=====的postProcessAfterInitialization方法 
=====Bean已经实例化执行初始化方法（init-method）后可以返回指定Bean的包装实例

从上面输入日志可以总结出后置处理器调用过程如下：
在这里插入图片描述
源码解析调用过程：（以下均为部分源码）

接口：InstantiationAwareBeanPostProcessor
方法1：postProcessBeforeInstantiation
得到bean实例前，返回代理，容器将实例化代理类

#1.org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(String, RootBeanDefinition, Object[]);
protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) throws BeanCreationException {

		try {
			Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
			if (bean != null) {
				return bean;
			}
		}
		catch (Throwable ex) {
			throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName,
					"BeanPostProcessor before instantiation of bean failed", ex);
		}
}

#2.org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.resolveBeforeInstantiation(String, RootBeanDefinition);
protected Object resolveBeforeInstantiation(String beanName, RootBeanDefinition mbd) {
		Object bean = null;
		if (!Boolean.FALSE.equals(mbd.beforeInstantiationResolved)) {
			// Make sure bean class is actually resolved at this point.
			if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
				Class<?> targetType = determineTargetType(beanName, mbd);
				if (targetType != null) {
					bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName);
					if (bean != null) {
						bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
					}
				}
			}
			mbd.beforeInstantiationResolved = (bean != null);
		}
		return bean;
	}

#3.org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsBeforeInstantiation(Class<?>, String);
protected Object applyBeanPostProcessorsBeforeInstantiation(Class<?> beanClass, String beanName) {
		for (BeanPostProcessor bp : getBeanPostProcessors()) {
			if (bp instanceof InstantiationAwareBeanPostProcessor) {
				InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
				Object result = ibp.postProcessBeforeInstantiation(beanClass, beanName);
				if (result != null) {
					return result;
				}
			}
		}
		return null;
	}

上面的方式，发现还是贴的代码太多，后面就只粘贴最后有个方法
接口：SmartInstantiationAwareBeanPostProcessor
方法2：determineCandidateConstructors
Bean实例化之前，推断Bean的构造方法

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(String, RootBeanDefinition, Object[])
——> org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(String, RootBeanDefinition, Object[])
——> org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(String, RootBeanDefinition, Object[])
——> org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.determineConstructorsFromBeanPostProcessors(Class<?>, String)
protected Constructor<?>[] determineConstructorsFromBeanPostProcessors(@Nullable Class<?> beanClass, String beanName)
			throws BeansException {

		if (beanClass != null && hasInstantiationAwareBeanPostProcessors()) {
			for (BeanPostProcessor bp : getBeanPostProcessors()) {
				if (bp instanceof SmartInstantiationAwareBeanPostProcessor) {
					SmartInstantiationAwareBeanPostProcessor ibp = (SmartInstantiationAwareBeanPostProcessor) bp;
					Constructor<?>[] ctors = ibp.determineCandidateConstructors(beanClass, beanName);
					if (ctors != null) {
						return ctors;
					}
				}
			}
		}
		return null;
	}

接口：MergedBeanDefinitionPostProcessor
方法3：postProcessMergedBeanDefinition
解析并缓存注解信息（@Autowired @Qualifier @Value）

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(String, RootBeanDefinition, Object[])
——> org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(String, RootBeanDefinition, Object[])
——> org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyMergedBeanDefinitionPostProcessors(RootBeanDefinition, Class<?>, String)
protected void applyMergedBeanDefinitionPostProcessors(RootBeanDefinition mbd, Class<?> beanType, String beanName) {
		for (BeanPostProcessor bp : getBeanPostProcessors()) {
			if (bp instanceof MergedBeanDefinitionPostProcessor) {
				MergedBeanDefinitionPostProcessor bdp = (MergedBeanDefinitionPostProcessor) bp;
				bdp.postProcessMergedBeanDefinition(mbd, beanType, beanName);
			}
		}
	}

接口：InstantiationAwareBeanPostProcessor
方法4：postProcessAfterInstantiation
Bean已经实例化但spring还没有注入属性，判断Bean是否需要跳过属性填充返回True则跳过属性填充

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(String, RootBeanDefinition, Object[])
——> org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(String, RootBeanDefinition, Object[])
——> org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(String, RootBeanDefinition, BeanWrapper)
protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {
	
		// Give any InstantiationAwareBeanPostProcessors the opportunity to modify the
		// state of the bean before properties are set. This can be used, for example,
		// to support styles of field injection.
		boolean continueWithPropertyPopulation = true;

		if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
			for (BeanPostProcessor bp : getBeanPostProcessors()) {
				if (bp instanceof InstantiationAwareBeanPostProcessor) {
					InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
					if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
						continueWithPropertyPopulation = false;
						break;
					}
				}
			}
	//后面代码省略
	}
}

接口：SmartInstantiationAwareBeanPostProcessor
方法5：getEarlyBeanReference
Bean完全初始化之前，返回Bean的一个引用对象，通常用于解决 循 环 依 赖 \color{red}{循环依赖} 问题

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(String, RootBeanDefinition, Object[])
——> org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(String, RootBeanDefinition, Object[])
——> org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.getEarlyBeanReference(String, RootBeanDefinition, Object)
protected Object getEarlyBeanReference(String beanName, RootBeanDefinition mbd, Object bean) {
		Object exposedObject = bean;
		if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
			for (BeanPostProcessor bp : getBeanPostProcessors()) {
				if (bp instanceof SmartInstantiationAwareBeanPostProcessor) {
					SmartInstantiationAwareBeanPostProcessor ibp = (SmartInstantiationAwareBeanPostProcessor) bp;
					exposedObject = ibp.getEarlyBeanReference(exposedObject, beanName);
				}
			}
		}
		return exposedObject;
	}

接口：InstantiationAwareBeanPostProcessor
方法6：postProcessProperties
Bean实例化后进行属性填充

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(String, RootBeanDefinition, Object[])
——> org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(String, RootBeanDefinition, Object[])
——> org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(String, RootBeanDefinition, BeanWrapper)
protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {
//省略代码
PropertyDescriptor[] filteredPds = null;
		if (hasInstAwareBpps) {
			if (pvs == null) {
				pvs = mbd.getPropertyValues();
			}
			for (BeanPostProcessor bp : getBeanPostProcessors()) {
				if (bp instanceof InstantiationAwareBeanPostProcessor) {
					InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
					PropertyValues pvsToUse = ibp.postProcessProperties(pvs, bw.getWrappedInstance(), beanName);
					if (pvsToUse == null) {
						if (filteredPds == null) {
							filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
						}
						pvsToUse = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
						if (pvsToUse == null) {
							return;
						}
					}
					pvs = pvsToUse;
				}
			}
		}
		//省略代码
}

接口：BeanPostProcessor
方法7：postProcessBeforeInitialization
Bean已经实例化执行初始化方法（init-method） 前 \color{red}{前} 可以返回指定Bean的包装实例

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org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(String, RootBeanDefinition, Object[])
——> org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(String, RootBeanDefinition, Object[])
——> org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(String, Object, RootBeanDefinition)
——> org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsBeforeInitialization(Object, String)
public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
			throws BeansException {

		Object result = existingBean;
		for (BeanPostProcessor processor : getBeanPostProcessors()) {
			Object current = processor.postProcessBeforeInitialization(result, beanName);
			if (current == null) {
				return result;
			}
			result = current;
		}
		return result;
	}

接口：BeanPostProcessor
方法8：postProcessAfterInitialization
Bean已经实例化执行初始化方法（init-method） 后 \color{red}{后} 可以返回指定Bean的包装实例

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(String, RootBeanDefinition, Object[])
——> org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(String, RootBeanDefinition, Object[])
——> org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(String, Object, RootBeanDefinition)
——> org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsAfterInitialization(Object, String)
public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
			throws BeansException {

		Object result = existingBean;
		for (BeanPostProcessor processor : getBeanPostProcessors()) {
			Object current = processor.postProcessAfterInitialization(result, beanName);
			if (current == null) {
				return result;
			}
			result = current;
		}
		return result;
	}
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