Spring学习笔记–源码解析aop代理对象创建流程

代理对象创建

AOP基础用例准备

Bean定义

@Component
public class LagouBean {
	 public void tech(){
	 System.out.println("java learning......");
	 }
}

Aspect定义

package com.lagou;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.aspectj.lang.annotation.Pointcut;
import org.springframework.stereotype.Component;
@Component
@Aspect
public class LagouAspect {
	 @Pointcut("execution(* com.lagou.*.*(..))")
	 public void pointcut(){
	 }
	 @Before("pointcut()")
	 public void before() {
	 	System.out.println("before method ......");
	 }
 }

测试

/**
* 测试⽤例：Aop 代理对象创建
*/
@Test
public void testAopProxyBuild(){
 ApplicationContext applicationContext = new AnnotationConfigApplicationContext(SpringConfig.class);
 LagouBean lagouBean = applicationContext.getBean(LagouBean.class);
 lagouBean.tech();
}

时机点分析

我们发现在 getBean 之前，LagouBean对象已经产⽣（即在第⼀⾏初始化代码中完成），⽽且该对象是⼀个代理对象（Cglib代理对象），我们断定，容器初始化过程中⽬标Ban已经完成了代理，返回了代理对象。

代理对象创建流程

AbstractAutowireCapableBeanFactory#initializeBean(java.lang.String, java.lang.Object,org.springframework.beans.factory.support.RootBeanDefinition)

/**
 *
 * 初始化Bean
 包括Bean后置处理器初始化
 Bean的⼀些初始化⽅法的执⾏init-method
 Bean的实现的声明周期相关接⼝的属性注⼊
 */
protected Object initializeBean(final String beanName, final Object bean,
	@Nullable RootBeanDefinition mbd) {
	 // 执⾏所有的AwareMethods
	 if (System.getSecurityManager() != null) {
		 AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
			 invokeAwareMethods(beanName, bean);
	 		return null;
		 }, getAccessControlContext());
	 }
	 else {
		 invokeAwareMethods(beanName, bean);
	 }
	 Object wrappedBean = bean;
	 if (mbd == null || !mbd.isSynthetic()) {
		 // 执⾏所有的BeanPostProcessor#postProcessBeforeInitialization 初始化之前的处理器⽅法
		 wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean,beanName);
	 }
	 try {
	 	// 这⾥就开始执⾏afterPropertiesSet（实现了InitializingBean接⼝）⽅法和
		initMethod invokeInitMethods(beanName, wrappedBean, mbd);
	 }
	 catch (Throwable ex) {
	 	throw new BeanCreationException(
	 	(mbd != null ? mbd.getResourceDescription() : null),beanName, "Invocation of init method failed", ex);
	 }
	 if (mbd == null || !mbd.isSynthetic()) {
		 // 整个Bean初始化完成，执⾏后置处理器⽅法
		 wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean,beanName);
	 }
	 return wrappedBean;
}

AbstractAutowireCapableBeanFactory#applyBeanPostProcessorsAfterInitialization

@Override
 public Object applyBeanPostProcessorsAfterInitialization(ObjectexistingBean, String beanName)
throws BeansException {
	Object result = existingBean;
	 // 循环执⾏后置处理器
	 for (BeanPostProcessor processor : getBeanPostProcessors()) {
		 Object current = processor.postProcessAfterInitialization(result,beanName);
		 if (current == null) {
			 return result;
		 }
			 result = current;
	 }
	 return result;
 }

创建代理对象的后置处理器AbstractAutoProxyCreator#postProcessAfterInitialization

/**
 * Create a proxy with the configured interceptors if the bean is
 * identified as one to proxy by the subclass.
 * @see #getAdvicesAndAdvisorsForBean
 */
 @Override
public Object postProcessAfterInitialization(@Nullable Object bean, String beanName) {
	 if (bean != null) {
		 // 检查下该类是否已经暴露过了（可能已经创建了，⽐如A依赖B时，创建A时候，就会先去创建B。
		 // 当真正需要创建B时，就没必要再代理⼀次已经代理过的对象）,避免重复创建
		 Object cacheKey = getCacheKey(bean.getClass(), beanName);
		 if (this.earlyProxyReferences.remove(cacheKey) != bean) {
		 	return wrapIfNecessary(bean, beanName, cacheKey);
		 }
	 }
	 return bean;
 }

AbstractAutoProxyCreator#wrapIfNecessary

/** Wrap the given bean if necessary, i.e. if it is eligible for being
proxied.
 * @param bean the raw bean instance
 * @param beanName the name of the bean
 * @param cacheKey the cache key for metadata access
 * @return a proxy wrapping the bean, or the raw bean instance as-is
 */
 protected Object wrapIfNecessary(Object bean, String beanName, Object
cacheKey) {
	 // targetSourcedBeans包含，说明前⾯创建过
	 if (StringUtils.hasLength(beanName) &&this.targetSourcedBeans.contains(beanName)) {
	 	return bean;
	 }
	 if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) {
	 	return bean;
	 }
	 if (isInfrastructureClass(bean.getClass()) || shouldSkip(bean.getClass(),beanName)) {
		 this.advisedBeans.put(cacheKey, Boolean.FALSE);
		 return bean;
	 }
	 // Create proxy if we have advice.
	 // 得到所有候选Advisor，对Advisors和bean的⽅法双层遍历匹配，最终得到⼀个
	 List<Advisor>，即specificInterceptors
	 Object[] specificInterceptors =
	 getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
	 if (specificInterceptors != DO_NOT_PROXY) {
	 	this.advisedBeans.put(cacheKey, Boolean.TRUE);
	 	// 重点，创建代理对象
	 	Object proxy = createProxy(bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));
	 	this.proxyTypes.put(cacheKey, proxy.getClass());
	 	return proxy;
	 }
	 this.advisedBeans.put(cacheKey, Boolean.FALSE);
	 return bean;
 }

AbstractAutoProxyCreator#createProxy

/**
 * Create an AOP proxy for the given bean.
 * 为指定 bean 创建代理对象
 */
 protected Object createProxy(Class<?> beanClass, @Nullable String beanName,@Nullable Object[] specificInterceptors, TargetSource targetSource) {
	 if (this.beanFactory instanceof ConfigurableListableBeanFactory) {
 		AutoProxyUtils.exposeTargetClass((ConfigurableListableBeanFactory)
		this.beanFactory, beanName, beanClass);
	 }
	 // 创建代理的⼯作交给ProxyFactory
	 ProxyFactory proxyFactory = new ProxyFactory();
	 proxyFactory.copyFrom(this);
	 // 根据⼀些情况判断是否要设置proxyTargetClass=true
	 if (!proxyFactory.isProxyTargetClass()) {
		 if (shouldProxyTargetClass(beanClass, beanName)) {
		 	proxyFactory.setProxyTargetClass(true);
		}else {
 		evaluateProxyInterfaces(beanClass, proxyFactory);
 		}
 	}
	 // 把指定和通⽤拦截对象合并, 并都适配成Advisor
	 Advisor[] advisors = buildAdvisors(beanName, specificInterceptors);
	 proxyFactory.addAdvisors(advisors);
	 // 设置参数
	 proxyFactory.setTargetSource(targetSource);
	 customizeProxyFactory(proxyFactory);
	 proxyFactory.setFrozen(this.freezeProxy);
	 if (advisorsPreFiltered()) {
	 	proxyFactory.setPreFiltered(true);
	 }
 	// 上⾯准备做完就开始创建代理
	 return proxyFactory.getProxy(getProxyClassLoader());
 }

接着跟进到ProxyFactory中

public class ProxyFactory extends ProxyCreatorSupport {
	 public Object getProxy(ClassLoader classLoader) {
		 // ⽤ProxyFactory创建AopProxy, 然后⽤AopProxy创建Proxy, 所以这⾥重要的是看获取的AopProxy
		 // 对象是什么,
		 // 然后进去看怎么创建动态代理, 提供了两种：jdk proxy, cglib
		 return createAopProxy().getProxy(classLoader);
	 }
}

public class ProxyCreatorSupport extends AdvisedSupport {
	 private AopProxyFactory aopProxyFactory;
	 
	 public ProxyCreatorSupport() {
	 	this.aopProxyFactory = new DefaultAopProxyFactory();
	 }
	 
	 protected final synchronized AopProxy createAopProxy() {
	 if (!this.active) {
		 activate();
	 }
	 //先获取创建AopProxy的⼯⼚, 再由此创建AopProxy
		 return getAopProxyFactory().createAopProxy(this);
	 }
	 
	 public AopProxyFactory getAopProxyFactory() {
	 	return this.aopProxyFactory;
	 }
}

流程就是⽤AopProxyFactory创建AopProxy, 再⽤AopProxy创建代理对象，这⾥的AopProxyFactory默认是DefaultAopProxyFactory，看他的createAopProxy⽅法

public class DefaultAopProxyFactory implements AopProxyFactory, Serializable {
	 @Override
	 public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {
	 if (config.isOptimize() || config.isProxyTargetClass() ||hasNoUserSuppliedProxyInterfaces(config)) {
	 	Class<?> targetClass = config.getTargetClass();
		 if (targetClass == null) {
			 throw new AopConfigException("TargetSource cannot determine targetclass: "+ "Either an interface or a target is required for proxycreation.");
		 }
		 if (targetClass.isInterface()) {
		 	return new JdkDynamicAopProxy(config);
		 }
	 	 return new ObjenesisCglibAopProxy(config);
	 } else {
		 	return new JdkDynamicAopProxy(config);
	 }
 }
	 /**
	 * Determine whether the supplied {@link AdvisedSupport} has only the
	 * {@link org.springframework.aop.SpringProxy} interface specified (or no* proxy interfaces specified at all).
	 */
	 private boolean hasNoUserSuppliedProxyInterfaces(AdvisedSupport config) {
	 Class<?>[] interfaces = config.getProxiedInterfaces();
	 return (interfaces.length == 0 || (interfaces.length == 1 &&SpringProxy.class.equals(interfaces[0])));
	 }
}

这⾥决定创建代理对象是⽤JDK Proxy，还是⽤ Cglib 了，最简单的从使⽤⽅⾯使⽤来说：设置proxyTargetClass=true强制使⽤Cglib 代理，什么参数都不设并且对象类实现了接⼝则默认⽤JDK 代理，如果没有实现接⼝则也必须⽤Cglib
ProxyFactory#getProxy(java.lang.ClassLoader)------ CglibAopProxy#getProxy(java.lang.ClassLoader)

@Override
 public Object getProxy(@Nullable ClassLoader classLoader) {
 	if (logger.isTraceEnabled()) {
 		logger.trace("Creating CGLIB proxy: " + this.advised.getTargetSource());
 	}
	 try {
 		Class<?> rootClass = this.advised.getTargetClass();
 		Assert.state(rootClass != null, "Target class must be available for creating a CGLIB proxy");
 		Class<?> proxySuperClass = rootClass;
 		if (ClassUtils.isCglibProxyClass(rootClass)) {
 			proxySuperClass = rootClass.getSuperclass();
 			Class<?>[] additionalInterfaces = rootClass.getInterfaces();
 			for (Class<?> additionalInterface : additionalInterfaces) {
 				this.advised.addInterface(additionalInterface);
			}
 		}
 		// Validate the class, writing log messages as necessary.
		validateClassIfNecessary(proxySuperClass, classLoader);
		 // 配置 Cglib 增强
		 Enhancer enhancer = createEnhancer();
		 if (classLoader != null) {
 			enhancer.setClassLoader(classLoader);
 			if (classLoader instanceof SmartClassLoader &&((SmartClassLoader)classLoader).isClassReloadable(proxySuperClass)) {
				 enhancer.setUseCache(false);
 			}
		}
 		enhancer.setSuperclass(proxySuperClass);
 
		enhancer.setInterfaces(AopProxyUtils.completeProxiedInterfaces(this.advised));
 		enhancer.setNamingPolicy(SpringNamingPolicy.INSTANCE);
 		enhancer.setStrategy(new
		ClassLoaderAwareUndeclaredThrowableStrategy(classLoader));
 		Callback[] callbacks = getCallbacks(rootClass);
 		Class<?>[] types = new Class<?>[callbacks.length];
 		for (int x = 0; x < types.length; x++) {
 			types[x] = callbacks[x].getClass();
 		}
 		// fixedInterceptorMap only populated at this point, after getCallbacks
		call above
 		enhancer.setCallbackFilter(new ProxyCallbackFilter(
 		this.advised.getConfigurationOnlyCopy(), this.fixedInterceptorMap,
		this.fixedInterceptorOffset));
 		enhancer.setCallbackTypes(types);
		 // ⽣成代理类，并且创建⼀个代理类的实例
		 return createProxyClassAndInstance(enhancer, callbacks);
 	}
 	catch (CodeGenerationException | IllegalArgumentException ex) {
		throw new AopConfigException("Could not generate CGLIB subclass of " +this.advised.getTargetClass() +": Common causes of this problem include using a final class or anon-visible class",ex);
 	}
 	catch (Throwable ex) {
 		// TargetSource.getTarget() failed
 		throw new AopConfigException("Unexpected AOP exception", ex);
 	}
}

AOP源码分析类方法调用关系过程中记录

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#i
nitializeBean
调用
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#a
pplyBeanPostProcessorsAfterInitialization
调用
org.springframework.aop.framework.autoproxy.AbstractAutoProxyCreator#postProce
ssAfterInitialization（后置处理器AbstractAutoProxyCreator完成bean代理对象创建）
调用
org.springframework.aop.framework.autoproxy.AbstractAutoProxyCreator#wrapIfNec
essary
调用
org.springframework.aop.framework.autoproxy.AbstractAutoProxyCreator#createPro
xy （在这⼀步把委托对象的aop增强和通⽤拦截进⾏合并，最终给代理对象）
调用
org.springframework.aop.framework.DefaultAopProxyFactory#createAopProxy
调用
org.springframework.aop.framework.CglibAopProxy#getProxy(java.lang.ClassLoader
)