1.美图

2.概述

寻找代理，请参考以前的文章

3.前文概要

/*** 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** 如果需要则包装该bean,例如该bean可以被代理*/protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {// 1、如果已经处理过或者不需要创建代理，则返回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.// 2、创建代理// 2.1 根据指定的bean获取所有的适合该bean的增强Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);if (specificInterceptors != DO_NOT_PROXY) {// 2.2 为指定bean创建代理this.advisedBeans.put(cacheKey, Boolean.TRUE);Object proxy = createProxy(bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));this.proxyTypes.put(cacheKey, proxy.getClass());return proxy;}// 3、缓存this.advisedBeans.put(cacheKey, Boolean.FALSE);return bean;}

这里第二步骤主要是创建代理

4.创建代理

/*** 为给定的bean创建代理** Create an AOP proxy for the given bean.* @param beanClass the class of the bean* @param beanName the name of the bean* @param specificInterceptors the set of interceptors that is* specific to this bean (may be empty, but not null)* @param targetSource the TargetSource for the proxy,* already pre-configured to access the bean* @return the AOP proxy for the bean* @see #buildAdvisors*/protected Object createProxy(Class<?> beanClass, @Nullable String beanName,@Nullable Object[] specificInterceptors, TargetSource targetSource) {// 1、当前beanFactory是ConfigurableListableBeanFactory类型，则尝试暴露当前bean的target classif (this.beanFactory instanceof ConfigurableListableBeanFactory) {AutoProxyUtils.exposeTargetClass((ConfigurableListableBeanFactory) this.beanFactory, beanName, beanClass);}// 2、创建ProxyFactory并配置ProxyFactory proxyFactory = new ProxyFactory();proxyFactory.copyFrom(this);// 是否直接代理目标类以及接口if (!proxyFactory.isProxyTargetClass()) {// 确定给定bean是否应该用它的目标类而不是接口进行代理if (shouldProxyTargetClass(beanClass, beanName)) {proxyFactory.setProxyTargetClass(true);}// 检查给定bean类上的接口，如果合适的话，将它们应用到ProxyFactory。即添加代理接口else {evaluateProxyInterfaces(beanClass, proxyFactory);}}// 3、确定给定bean的advisors，包括特定的拦截器和公共拦截器，是否适配Advisor接口。Advisor[] advisors = buildAdvisors(beanName, specificInterceptors);// 设置增强proxyFactory.addAdvisors(advisors);// 设置代理目标proxyFactory.setTargetSource(targetSource);// 定制proxyFactory（空的模板方法，可在子类中自己定制）customizeProxyFactory(proxyFactory);// 锁定proxyFactoryproxyFactory.setFrozen(this.freezeProxy);if (advisorsPreFiltered()) {proxyFactory.setPreFiltered(true);}// 4、创建代理return proxyFactory.getProxy(getProxyClassLoader());}

4.1 创建代理的具体过程

	public Object getProxy(@Nullable ClassLoader classLoader) {return createAopProxy().getProxy(classLoader);}/*** Subclasses should call this to get a new AOP proxy. They should <b>not</b>* create an AOP proxy with {@code this} as an argument.*/protected final synchronized AopProxy createAopProxy() {if (!this.active) {activate();}return getAopProxyFactory().createAopProxy(this);}

从上面的代码可以看到，创建代理的具体工作委托给了AopProxyFactory的createAopProxy方法。

public class DefaultAopProxyFactory implements AopProxyFactory, Serializable {@Overridepublic AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {// 1、判断是否需要创建CGLIB动态代理if (config.isOptimize() || config.isProxyTargetClass() || hasNoUserSuppliedProxyInterfaces(config)) {Class<?> targetClass = config.getTargetClass();if (targetClass == null) {throw new AopConfigException("TargetSource cannot determine target class: " +"Either an interface or a target is required for proxy creation.");}// todo 这里有疑问 即// targetClass.isInterface()// Proxy.isProxyClass(targetClass)// 什么情况下会生效if (targetClass.isInterface() || Proxy.isProxyClass(targetClass)) {// 创建jdk动态代理return new JdkDynamicAopProxy(config);}// 创建CGLIB动态代理return new ObjenesisCglibAopProxy(config);}// 2、默认创建JDK动态代理else {return new JdkDynamicAopProxy(config);}}

这里我们终于看到了判断CGLIB和JDK动态代理的判断条件，这也是面试会碰到的一个常见的问题。

判断是否需要创建CGLIB动态代理

1. config.isOptimize()：判断通过CGLIB创建的代理是否使用了优化策略
   该条件取值于ProxyConfig类的optimize属性。此属性标记是否对代理进行优化。启动优化通常意味着在代理对象被创建后，增强的修改将不会生效，因此默认值为false。如果exposeProxy设置为true，即使optimize为true也会被忽略。
2. config.isProxyTargetClass()：是否配置了proxy-target-class为true
   该条件取值于ProxyConfig类的proxyTargetClass属性。此属性标记是否直接对目标类进行代理，而不是通过接口产生代理。
3. hasNoUserSuppliedProxyInterfaces(config)：是否存在代理接口

满足以上三者条件的任何一个，则会考虑开启CGLIB动态代理，但是在该if条件里还有另外一层判断 targetClass.isInterface() || Proxy.isProxyClass(targetClass),即如果目标类本身就是一个接口，或者目标类是由Proxy.newProxyInstance()或Proxy.getProxyClass()生成时，则依然采用jdk动态代理。

4.2 获取CGLIB动态代理

	@Overridepublic 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);// Configure CGLIB Enhancer...// 新建并配置EnhancerEnhancer 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 aboveenhancer.setCallbackFilter(new ProxyCallbackFilter(this.advised.getConfigurationOnlyCopy(), this.fixedInterceptorMap, this.fixedInterceptorOffset));enhancer.setCallbackTypes(types);// Generate the proxy class and create a proxy instance.// 生成代理类并创建代理实例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 a non-visible class",ex);}catch (Throwable ex) {// TargetSource.getTarget() failedthrow new AopConfigException("Unexpected AOP exception", ex);}}

紧接着看 Spring ： Spring Aop CGLIB动态代理调用过程

4.3 获取JDK动态代理

@Overridepublic Object getProxy(@Nullable ClassLoader classLoader) {if (logger.isTraceEnabled()) {logger.trace("Creating JDK dynamic proxy: " + this.advised.getTargetSource());}// 确定用于给定AOP配置的代理的完整接口集。Class<?>[] proxiedInterfaces = AopProxyUtils.completeProxiedInterfaces(this.advised, true);// 判断被代理接口有没有重写equals和hashCode方法findDefinedEqualsAndHashCodeMethods(proxiedInterfaces);// 为接口创建代理return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);}

紧接着看 Spring ： Spring Aop JDK动态代理调用过程