spring源码学习之AOP（二）

　　接着上一篇中的内容！

3、创建代理

在获取了所有的bean对应的增强器之后，便可以进行代理的创建了
org.springframework.aop.framework.autoproxy包下的AbstractAutoProxyCreator类中的createProxy方法

 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);
     }

     ProxyFactory proxyFactory = new ProxyFactory();
     // 获取当前类中的相关属性
     proxyFactory.copyFrom(this);

     // 决定对于给定的bean是否应该使用targetClass属性，而不是他的接口代理，检查proxyTargetClass设置以及preserveTargetClass属性
     if (!proxyFactory.isProxyTargetClass()) {
         if (shouldProxyTargetClass(beanClass, beanName)) {
             proxyFactory.setProxyTargetClass(true);
         }
         else {
             // 添加代理接口
             evaluateProxyInterfaces(beanClass, proxyFactory);
         }
     }

     Advisor[] advisors = buildAdvisors(beanName, specificInterceptors);
     // 加入增强器
     proxyFactory.addAdvisors(advisors);
     // 设置要代理的类
     proxyFactory.setTargetSource(targetSource);
     // 定制代理
     customizeProxyFactory(proxyFactory);
     // 用来控制代理工厂被配置之后，是否还允许修改通知
     // 缺省值为false（即在代理被设置之后，不允许修改代理的配置）
     proxyFactory.setFrozen(this.freezeProxy);
     if (advisorsPreFiltered()) {
         proxyFactory.setPreFiltered(true);
     }

     return proxyFactory.getProxy(getProxyClassLoader());
 }

对于代理类的创建和处理，spring委托给ProxyFactory处理，而此函数中主要是对ProxyFactory的初始化操作，进而对真正的创建代理做准备，这些初始化操作如下：
（1）获取当前类中的属性
（2）添加代理接口
（3）封装advisor并加入到ProxyFactory中
（4）设置要代理的类
（5）当然spring中还为子类提供了定制的函数customizeProxyFactory，子类在此函数中对ProxyFactory进一步封装
（6）进行获取代理操作

其中封装advisor并加入到ProxyFactory中以及创建代理是两个相对繁琐的过程，可以通过ProxyFactory提供的addAdvisor方法直接将增强器置入代理创建工厂中，
但是将拦截器封装成增强器还是需要一定的逻辑的

org.springframework.aop.framework.autoproxy包下的AbstractAutoProxyCreator类

 protected Advisor[] buildAdvisors(@Nullable String beanName, @Nullable Object[] specificInterceptors) {
     // Handle prototypes correctly...
     // 解析注册的所有的InterceptorName
     Advisor[] commonInterceptors = resolveInterceptorNames();

     List<Object> allInterceptors = new ArrayList<>();
     if (specificInterceptors != null) {
         // 加入拦截器
         allInterceptors.addAll(Arrays.asList(specificInterceptors));
         if (commonInterceptors.length > 0) {
             if (this.applyCommonInterceptorsFirst) {
                 allInterceptors.addAll(0, Arrays.asList(commonInterceptors));
             }
             else {
                 allInterceptors.addAll(Arrays.asList(commonInterceptors));
             }
         }
     }
     if (logger.isDebugEnabled()) {
         int nrOfCommonInterceptors = commonInterceptors.length;
         int nrOfSpecificInterceptors = (specificInterceptors != null ? specificInterceptors.length : 0);
         logger.debug("Creating implicit proxy for bean '" + beanName + "' with " + nrOfCommonInterceptors +
                 " common interceptors and " + nrOfSpecificInterceptors + " specific interceptors");
     }

     Advisor[] advisors = new Advisor[allInterceptors.size()];
     for (int i = 0; i < allInterceptors.size(); i++) {
         // 拦截器进行封装转化为Advisor
         advisors[i] = this.advisorAdapterRegistry.wrap(allInterceptors.get(i));
     }
     return advisors;
 }

wrap方法在org.springframework.aop.framework.adapter.DefaultAdvisorAdapterRegistry类中重写

 @Override
 public Advisor wrap(Object adviceObject) throws UnknownAdviceTypeException {
     // 如果要封装的对象本身就是Advisor类型的，无需做过多的处理
     if (adviceObject instanceof Advisor) {
         return (Advisor) adviceObject;
     }
     // 因为此封装方法只对Advisor和Advice两种类型有效，不是的话，就抛出异常
     if (!(adviceObject instanceof Advice)) {
         throw new UnknownAdviceTypeException(adviceObject);
     }
     Advice advice = (Advice) adviceObject;
     if (advice instanceof MethodInterceptor) {
         // So well-known it doesn't even need an adapter.
         // 如果是MethodInterceptor类型，则使用DefaultPointcutAdvisor类封装
         return new DefaultPointcutAdvisor(advice);
     }
     // 如果存在Advisor的适配器那么也同样需要进行封装
     for (AdvisorAdapter adapter : this.adapters) {
         // Check that it is supported.
         if (adapter.supportsAdvice(advice)) {
             return new DefaultPointcutAdvisor(advice);
         }
     }
     throw new UnknownAdviceTypeException(advice);
 }

由于spring中涉及过多的拦截器、增强器、增强方法等方式来对逻辑进行增强，所以非常有必要统一封装成Advisor来进行代理的创建，完成了增强的封装过程，那么解析的
最重要的一步就是代理的创建和获取了

（1）创建代理

 // org.springframework.aop.framework.ProxyFactory类中的
 public Object getProxy(@Nullable ClassLoader classLoader) {
     return createAopProxy().getProxy(classLoader);
 }

 protected final synchronized AopProxy createAopProxy() {
     if (!this.active) {
         activate();
     }
     // 创建代理
     return getAopProxyFactory().createAopProxy(this);
 }
 // org.springframework.aop.framework.DefaultAopProxyFactory类对createAopProxy()方法进行了重写

 @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 target class: " +
                     "Either an interface or a target is required for proxy creation.");
         }
         if (targetClass.isInterface() || Proxy.isProxyClass(targetClass)) {
             return new JdkDynamicAopProxy(config);
         }
         return new ObjenesisCglibAopProxy(config);
     }
     else {
         return new JdkDynamicAopProxy(config);
     }
 }

从源码可以看出，spring中存在着两种代理JdkDynamicAopProxy和ObjenesisCglibAopProxy两种
看一下createAopProxy方法中影响这spring使用何种代理的判断条件，也就是if中的条件
（1）isOptimize
用来控制通过CGLIB创建的代理是否使用激进的优化策略。除非了解AOP代理如何处理优化，否则不推荐使用这个设置，目前这个属性仅用于CGLIB代理，JDK代理无效
（2）isProxyTargetClass
这个属性为true时，目标类本身被代理而不是目标类的接口，如果这个属性设置为true，CGLIB代理将被创建，设置方式<aop:aspectj-autoproxy proxy-target-class="true" />
（3）hasNoUserSuppliedProxyInterfaces
是否存在代理接口

JDK代理与CGLIB代理的总结：
　　如果目标对象实现了接口，默认情况下会使用JDK动态代理实现AOP
　　如果目标对象实现了接口，可以强制使用CGLIB实现AOP
　　如果目标对象没有实现接口，必须采用CGLIB库，spring会自动在JDK动态代理和CGLIB代理之前切换

（2）获取代理

　　JDK代理使用案例

 // 创建业务接口，业务对外提供的接口，包含着业务可以对外提供的功能
 public interface UserService{

     // 目标方法
     public abstract void add();
 }

 // 创建业务接口实现类
 public class UserServiceImpl implements UserService {

     public void add(){
         System.out.println("---------add()----------");
     }
 }

 // 创建自定义的InvocationHandler，用于对接口提供的方法进行增强
 public class MyInvocationHandler implements InvocationHandler{
     private Object target;

     public MyInvocationHandler(Object target){
         super();
         this.target = target;
     }

     // 执行目标对象方法
     public Object invoke(Obejct proxy, Method method, Object[] args) throws Throwable {
         System.out.println("---------before()----------");
         Obejct result = method.invoke(target, args);
         System.out.println("---------after()----------");
         return result;
     }

     // 获取目标对象的代理对象
     public Object getProxy(){
         return Proxy.newProxyInstance(Thread.currentThread().getContextClassLoader(),target.getClass().getInterfaces(),this);
     }
 }

 // 测试类
 public class ProxyTest{

     @Test
     public void testProxy(){
         UserService userService = new UserServiceImpl();
         // 实例化InvocationHandler
         MyInvocationHandler invocationHandler = new MyInvocationHandler(userService);
         // 根据目标对象生成代理对象
         UserService proxy = (UserService) invocationHandler.getProxy();
         // 执行代理对象方法
         proxy.add();
     }
 }

用起来很简单，这其实就是AOP的简单的实现，在目标方法的执行之前和执行之后进行了增强，spring的AOP实现其实也就是用了Proxy、InvocationHandler这两个类
再次回顾一下使用JDK代理的方式，在整个创建过程中，对于InvocationHandler的创建是最为核心的，在自定义的InvocationHandler中需要重写三个函数
　　构造函数，将代理对象传入
　　invoke方法，此方法中实现了AOP增强的所有逻辑
　　getProxy方法

JdkDynamicAopProxy的getProxy()源码：
org.springframework.aop.framework.JdkDynamicAopProxy类中

 @Override
 public Object getProxy(@Nullable ClassLoader classLoader) {
     if (logger.isDebugEnabled()) {
         logger.debug("Creating JDK dynamic proxy: target source is " + this.advised.getTargetSource());
     }
     Class<?>[] proxiedInterfaces = AopProxyUtils.completeProxiedInterfaces(this.advised, true);
     findDefinedEqualsAndHashCodeMethods(proxiedInterfaces);
     return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);
 }

JDKProxy的使用关键是创建自定义的InvocationHandler，而InvocationHandler中包含了需要覆盖的函数getProxy，并且JdkDynamicAopProxy还实现了InvocationHandler接口，
因此，在该类中肯定存在一个重写的invoke方法，完成AOP的核心逻辑：invoke函数源码：

 @Override
 @Nullable
 public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
     Object oldProxy = null;
     boolean setProxyContext = false;

     TargetSource targetSource = this.advised.targetSource;
     Object target = null;

     try {
         // equals方法的处理
         if (!this.equalsDefined && AopUtils.isEqualsMethod(method)) {
             // The target does not implement the equals(Object) method itself.
             return equals(args[0]);
         }
         // hash方法的处理
         else if (!this.hashCodeDefined && AopUtils.isHashCodeMethod(method)) {
             // The target does not implement the hashCode() method itself.
             return hashCode();
         }
         else if (method.getDeclaringClass() == DecoratingProxy.class) {
             // There is only getDecoratedClass() declared -> dispatch to proxy config.
             return AopProxyUtils.ultimateTargetClass(this.advised);
         }
         else if (!this.advised.opaque && method.getDeclaringClass().isInterface() &&
                 method.getDeclaringClass().isAssignableFrom(Advised.class)) {
             // Service invocations on ProxyConfig with the proxy config...
             return AopUtils.invokeJoinpointUsingReflection(this.advised, method, args);
         }

         Object retVal;

         // 有时候目标对象内部的自我调用将无法实施切面中的增强，则需要此属性暴露代理
         if (this.advised.exposeProxy) {
             // Make invocation available if necessary.
             oldProxy = AopContext.setCurrentProxy(proxy);
             setProxyContext = true;
         }

         // Get as late as possible to minimize the time we "own" the target,
         // in case it comes from a pool.
         target = targetSource.getTarget();
         Class<?> targetClass = (target != null ? target.getClass() : null);

         // Get the interception chain for this method.
         // 获取当前方法的拦截器链
         List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);

         // Check whether we have any advice. If we don't, we can fallback on direct
         // reflective invocation of the target, and avoid creating a MethodInvocation.
         if (chain.isEmpty()) {
             // We can skip creating a MethodInvocation: just invoke the target directly
             // Note that the final invoker must be an InvokerInterceptor so we know it does
             // nothing but a reflective operation on the target, and no hot swapping or fancy proxying.
             // 如果没有发现拦截器链，那么直接调用切点方法
             Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
             retVal = AopUtils.invokeJoinpointUsingReflection(target, method, argsToUse);
         }
         else {
             // We need to create a method invocation...
             // 将拦截器封装在ReflectiveMethodInvocation以便于其使用proceed进行链接表用拦截器
             MethodInvocation invocation =
                     new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain);
             // Proceed to the joinpoint through the interceptor chain.
             // 执行拦截器链
             retVal = invocation.proceed();
         }

         // Massage return value if necessary.
         // 返回结果
         Class<?> returnType = method.getReturnType();
         if (retVal != null && retVal == target &&
                 returnType != Object.class && returnType.isInstance(proxy) &&
                 !RawTargetAccess.class.isAssignableFrom(method.getDeclaringClass())) {
             // Special case: it returned "this" and the return type of the method
             // is type-compatible. Note that we can't help if the target sets
             // a reference to itself in another returned object.
             retVal = proxy;
         }
         else if (retVal == null && returnType != Void.TYPE && returnType.isPrimitive()) {
             throw new AopInvocationException(
                     "Null return value from advice does not match primitive return type for: " + method);
         }
         return retVal;
     }
     finally {
         if (target != null && !targetSource.isStatic()) {
             // Must have come from TargetSource.
             targetSource.releaseTarget(target);
         }
         if (setProxyContext) {
             // Restore old proxy.
             AopContext.setCurrentProxy(oldProxy);
         }
     }
 }

上面的方法中最主要的就是创建了一个拦截器链，并使用ReflectiveMethodInvocation类进行了封装，而在ReflectiveMethodInvocation的proceed中实现了拦截器的逐一
调用，那继续看proceed方法的源码，如何实现前置增强与后置增强的：

此方法是在org.springframework.aop.framework.ReflectiveMethodInvocation类中进行重写的：

 @Override
 @Nullable
 public Object proceed() throws Throwable {
     //    We start with an index of -1 and increment early.
     // 执行完所有增强后，执行切点方法
     if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) {
         return invokeJoinpoint();
     }

     // 获取下一个要执行的拦截器
     Object interceptorOrInterceptionAdvice =
             this.interceptorsAndDynamicMethodMatchers.get(++this.currentInterceptorIndex);
     if (interceptorOrInterceptionAdvice instanceof InterceptorAndDynamicMethodMatcher) {
         // Evaluate dynamic method matcher here: static part will already have
         // been evaluated and found to match.
         // 动态匹配
         InterceptorAndDynamicMethodMatcher dm =
                 (InterceptorAndDynamicMethodMatcher) interceptorOrInterceptionAdvice;
         if (dm.methodMatcher.matches(this.method, this.targetClass, this.arguments)) {
             return dm.interceptor.invoke(this);
         }
         else {
             // Dynamic matching failed.
             // Skip this interceptor and invoke the next in the chain.
             // 不匹配则不执行拦截器
             return proceed();
         }
     }
     else {
         // It's an interceptor, so we just invoke it: The pointcut will have
         // been evaluated statically before this object was constructed.
         /**
          * 普通拦截器则直接调用拦截器
          * 例如：
          * MethodBeforeAdviceIntercepter
          * AspectJAroundAdvice
          * AspectJAfterAdvice
          */
         // 将this作为参数传递以保证当前实例中调用链的执行
         return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);
     }
 }

　　CGLIB代理使用案例

CGLIB是一个强大的高性能的代码生成包。CGLIB包的底层是通过使用一个小而快的字节码处理框架ASM，来转换字节码并生成新的类。
看如何使用CGLIB
需要导入外部net.sf.cglib.proxy包

 public class EnhancerDemo{
     public static void main(String[] args){
         Enhancer enhancer = new Enhancer();
         enhancer.setSupperclass(EnhancerDemo.class);
         enhancer.setCallback(new MethodInterceptorImpl());
         EnhancerDemo demo = (EnhancerDemo) enhancer.create();
         demo.test();
         System.out.println(demo);
     }

     public void test(){
         System.out.println("EnhancerDemo test()");
     }

     public static class MethodInterceptorImpl implements MethodInterceptor{
         @Override
         public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy){
             System.out.println("Before invoke" + method);
             Object result = proxy.invokeSuper(obj, args);
             System.out.println("After invoke" + method);
             return result;
         }
     }
 }

完成CGLIB代理的类是委托给Cglib2AopProxy类去实现的，Cglib2AopProxy的入口应该是getProxy，也就是说Cglib2AopProxy类的getProxy中实现了Enhancer的创建和接口封装
我就有点搞不懂了，作者从哪里搞出来一个Cglib2AopProxy，明明是CglibAopProxy，看getProxy的源码
org.springframework.aop.framework.CglibAopProxy类中的getProxy

 @Override
 public Object getProxy(@Nullable ClassLoader classLoader) {
     if (logger.isDebugEnabled()) {
         logger.debug("Creating CGLIB proxy: target source is " + 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.
         // 验证Class
         validateClassIfNecessary(proxySuperClass, classLoader);

         // Configure CGLIB Enhancer...
         // 创建和配置Enhancer
         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));

         // 设置拦截器
         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);

         // Generate the proxy class and create a proxy instance.
         // 生成代理类和创建代理
         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() failed
         throw new AopConfigException("Unexpected AOP exception", ex);
     }
 }

以上函数完成的说明了spring中创建Enhancer的过程，这里最重要的是getCallbacks设置拦截器链，看getCallbacks的源码：
org.springframework.aop.framework.CglibAopProxy类中：

 private Callback[] getCallbacks(Class<?> rootClass) throws Exception {
     // Parameters used for optimization choices...
     // 对expose-proxy属性的处理
     boolean exposeProxy = this.advised.isExposeProxy();
     boolean isFrozen = this.advised.isFrozen();
     boolean isStatic = this.advised.getTargetSource().isStatic();

     // Choose an "aop" interceptor (used for AOP calls).
     // 将拦截器封装在DynamicAdvisedInterceptor中
     Callback aopInterceptor = new DynamicAdvisedInterceptor(this.advised);

     // Choose a "straight to target" interceptor. (used for calls that are
     // unadvised but can return this). May be required to expose the proxy.
     Callback targetInterceptor;
     if (exposeProxy) {
         targetInterceptor = (isStatic ?
                 new StaticUnadvisedExposedInterceptor(this.advised.getTargetSource().getTarget()) :
                 new DynamicUnadvisedExposedInterceptor(this.advised.getTargetSource()));
     }
     else {
         targetInterceptor = (isStatic ?
                 new StaticUnadvisedInterceptor(this.advised.getTargetSource().getTarget()) :
                 new DynamicUnadvisedInterceptor(this.advised.getTargetSource()));
     }

     // Choose a "direct to target" dispatcher (used for
     // unadvised calls to static targets that cannot return this).
     Callback targetDispatcher = (isStatic ?
             new StaticDispatcher(this.advised.getTargetSource().getTarget()) : new SerializableNoOp());

     Callback[] mainCallbacks = new Callback[] {
             // 将拦截器链加入到Callback中
             aopInterceptor,  // for normal advice
             targetInterceptor,  // invoke target without considering advice, if optimized
             new SerializableNoOp(),  // no override for methods mapped to this
             targetDispatcher, this.advisedDispatcher,
             new EqualsInterceptor(this.advised),
             new HashCodeInterceptor(this.advised)
     };

     Callback[] callbacks;

     // If the target is a static one and the advice chain is frozen,
     // then we can make some optimizations by sending the AOP calls
     // direct to the target using the fixed chain for that method.
     if (isStatic && isFrozen) {
         Method[] methods = rootClass.getMethods();
         Callback[] fixedCallbacks = new Callback[methods.length];
         this.fixedInterceptorMap = new HashMap<>(methods.length);

         // TODO: small memory optimization here (can skip creation for methods with no advice)
         for (int x = 0; x < methods.length; x++) {
             List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(methods[x], rootClass);
             fixedCallbacks[x] = new FixedChainStaticTargetInterceptor(
                     chain, this.advised.getTargetSource().getTarget(), this.advised.getTargetClass());
             this.fixedInterceptorMap.put(methods[x].toString(), x);
         }

         // Now copy both the callbacks from mainCallbacks
         // and fixedCallbacks into the callbacks array.
         callbacks = new Callback[mainCallbacks.length + fixedCallbacks.length];
         System.arraycopy(mainCallbacks, 0, callbacks, 0, mainCallbacks.length);
         System.arraycopy(fixedCallbacks, 0, callbacks, mainCallbacks.length, fixedCallbacks.length);
         this.fixedInterceptorOffset = mainCallbacks.length;
     }
     else {
         callbacks = mainCallbacks;
     }
     return callbacks;
 }

在getCallbacks中spring考虑了很多情况，但是对于我们来说，只需要理解最常用的就可以了，比如将advised属性封装在DynamicAdvisedInterceptor并加入在
callbacks中，这么做的目的是什么，为什么会这么做？在前面的示例中，我们了解到CGLIB中对于方法的拦截是通过将自定义的拦截器（实现MethodInterceptor接口）加入
Callback中并在调用代理的时候直接激活拦截器中的intercept方法来实现的，那么在getCallback中正是实现了这样的一个目的，DynamicAdvisedInterceptor继承自MethodInterceptor
加入CallBack中后，再次调用代理时会直接调用DynamicAdvisedInterceptor中的intercept方法，所以，由此推断，对于CGLIB方式实现的代理，其核心逻辑在
DynamicAdvisedInterceptor中的intercept方法，DynamicAdvisedInterceptor作为CglibAopProxy内部封装私有类，其在org.springframework.aop.framework.CglibAopProxy类中：

 @Override
 @Nullable
 public Object intercept(Object proxy, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
     Object oldProxy = null;
     boolean setProxyContext = false;
     Object target = null;
     TargetSource targetSource = this.advised.getTargetSource();
     try {
         if (this.advised.exposeProxy) {
             // Make invocation available if necessary.
             oldProxy = AopContext.setCurrentProxy(proxy);
             setProxyContext = true;
         }
         // Get as late as possible to minimize the time we "own" the target, in case it comes from a pool...
         target = targetSource.getTarget();
         Class<?> targetClass = (target != null ? target.getClass() : null);
         // 获取拦截链
         List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);
         Object retVal;
         // Check whether we only have one InvokerInterceptor: that is,
         // no real advice, but just reflective invocation of the target.
         if (chain.isEmpty() && Modifier.isPublic(method.getModifiers())) {
             // We can skip creating a MethodInvocation: just invoke the target directly.
             // Note that the final invoker must be an InvokerInterceptor, so we know
             // it does nothing but a reflective operation on the target, and no hot
             // swapping or fancy proxying.
             Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
             // 如果拦截链为空则直接激活原方法
             retVal = methodProxy.invoke(target, argsToUse);
         }
         else {
             // We need to create a method invocation...
             // 进入链中
             retVal = new CglibMethodInvocation(proxy, target, method, args, targetClass, chain, methodProxy).proceed();
         }
         retVal = processReturnType(proxy, target, method, retVal);
         return retVal;
     }
     finally {
         if (target != null && !targetSource.isStatic()) {
             targetSource.releaseTarget(target);
         }
         if (setProxyContext) {
             // Restore old proxy.
             AopContext.setCurrentProxy(oldProxy);
         }
     }
 }

上述的实现与JDK方式实现代理中的invoke方法基本相同，都是首先构造链，然后封装此链进行串联调用，区别就是在JDK代理中直接构造ReflectiveMethodInvocation类，而在
CGLIB代理中使用CglibMethodInvocation，CglibMethodInvocation继承自ReflectiveMethodInvocation，但是process方法没有重写

注意：spring还支持静态代理，这里没有写！！！不想写了