Spring源码-InstantiationAwareBeanPostProcessor

InstantiationAwareBeanPostProcessor

理解：InstantiationAwareBeanPostProcessor继承自BeanPostProcessor,常用于Bean实例化前生成代理对象，直接返回代理对象;

public interface InstantiationAwareBeanPostProcessor extends BeanPostProcessor {

	// Bean实例化前,可以在此方法中生成代理对象
	@Nullable
	default Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {
		return null;
	}

	// Bean实例化后
	default boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {
		return true;
	}

	// 设置Bean的属性
	@Nullable
	default PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName)
			throws BeansException {

		return null;
	}

	@Deprecated
	@Nullable
	default PropertyValues postProcessPropertyValues(
			PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) throws BeansException {

		return pvs;
	}

}

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

	// bean初始化之前
	@Nullable
	default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
		return bean;
	}

}

调用流程

1.在实例化bean之前,给BeanPostProcessors一个机会返回代理对象

protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
			throws BeanCreationException {
	try {
		// Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
		// 在实例化bean之前,给BeanPostProcessors一个机会返回代理对象
		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);
	}

	try {
		Object beanInstance = doCreateBean(beanName, mbdToUse, args);
		if (logger.isTraceEnabled()) {
			logger.trace("Finished creating instance of bean '" + beanName + "'");
		}
		return beanInstance;
	}
	catch (BeanCreationException | ImplicitlyAppearedSingletonException ex) {
		// A previously detected exception with proper bean creation context already,
		// or illegal singleton state to be communicated up to DefaultSingletonBeanRegistry.
		throw ex;
	}
	catch (Throwable ex) {
		throw new BeanCreationException(
				mbdToUse.getResourceDescription(), beanName, "Unexpected exception during bean creation", ex);
	}
}

2.执行InstantiationAwareBeanPostProcessors的Before方法返回Bean对象

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) {
				// 执行InstantiationAwareBeanPostProcessors的Before方法
				bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName);
				if (bean != null) {
					// 执行InstantiationAwareBeanPostProcessors的After方法
					bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
				}
			}
		}
		mbd.beforeInstantiationResolved = (bean != null);
	}
	return bean;
}

代码案例

public class BeforeInstantiation {

    public void doSomeThing(){
        System.out.println("执行do some thing ...");
    }
}

import org.springframework.cglib.proxy.MethodInterceptor;
import org.springframework.cglib.proxy.MethodProxy;
import java.lang.reflect.Method;

public class MyMethodInterceptor implements MethodInterceptor {
    @Override
    public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
        System.out.println("目标方法前："+method);
        Object o1 = methodProxy.invokeSuper(o, objects);
        System.out.println("目标方法后："+method);
        return o1;
    }
}

import org.springframework.beans.BeansException;
import org.springframework.beans.PropertyValues;
import org.springframework.beans.factory.config.InstantiationAwareBeanPostProcessor;
import org.springframework.cglib.proxy.Enhancer;

public class MyInstantiationAwareBeanPostProcessor  implements InstantiationAwareBeanPostProcessor {

    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        System.out.print("beanName:"+beanName+"执行..postProcessBeforeInitialization\n");

        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        System.out.print("beanName:"+beanName+"执行..postProcessAfterInitialization\n");

        return bean;
    }

    @Override
    public boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {
        System.out.print("beanName:"+beanName+"执行..postProcessAfterInstantiation\n");

        return false;
    }

    @Override
    public Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {
        System.out.print("beanName:"+beanName+"执行..postProcessBeforeInstantiation\n");
        //利用 其 生成动态代理
        if(beanClass==BeforeInstantiation.class){
            Enhancer enhancer = new Enhancer();
            enhancer.setSuperclass(beanClass);
            enhancer.setCallback(new MyMethodInterceptor());
            BeforeInstantiation beforeInstantiation = (BeforeInstantiation)enhancer.create();
            System.out.print("返回动态代理\n");
            return beforeInstantiation;
        }
        return null;
    }

    @Override
    public PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName) throws BeansException {
        System.out.print("beanName:"+beanName+"执行..postProcessProperties\n");
        return pvs;
    }
}

<?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.xsd">

    <bean id="beforeInstantiation" class="com.lixiang.resolveBeforeInstantiation.BeforeInstantiation"></bean>
    <bean id="myInstantiationAwareBeanPostProcessor" class="com.lixiang.resolveBeforeInstantiation.MyInstantiationAwareBeanPostProcessor"></bean>
</beans>

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Test {
    public static void main(String[] args) {
        ApplicationContext ac = new ClassPathXmlApplicationContext("resolveBeforeInstantiation.xml");
        BeforeInstantiation bean = ac.getBean(BeforeInstantiation.class);
        bean.doSomeThing();
    }
}