概述
下面是一个简单的使用ProxyFactoryBean实现AOP的例子。
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.1.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.1.xsd"
>
<description>Spring公共配置 </description>
<bean id = "testTarget" class = "com.sjj.aop.TestTarget"></bean>
<bean id = "testAdvice1" class = "com.sjj.aop.TestAdvice1"></bean>
<bean id = "testAdvice2" class = "com.sjj.aop.TestAdvice2"></bean>
<bean id = "testPointcut" class = "org.springframework.aop.support.JdkRegexpMethodPointcut">
<property name="pattern" value = ".*itest"/>
</bean>
<bean id = "testAdvisor1" class = "org.springframework.aop.support.DefaultPointcutAdvisor">
<property name="advice" ref="testAdvice1"/>
<property name="pointcut" ref="testPointcut"/>
</bean>
<bean id = "testAdvisor2" class = "org.springframework.aop.support.DefaultPointcutAdvisor">
<property name="advice" ref="testAdvice2"/>
<property name="pointcut" ref="testPointcut"/>
</bean>
<bean id = "testAop" class = "org.springframework.aop.framework.ProxyFactoryBean" lazy-init="true">
<!-- <property name="proxyInterfaces" value = "com.sjj.aop.TestInterface" /> -->
<property name="target" ref = "testTarget"/>
<property name="interceptorNames" >
<list>
<value>testAdvisor1</value>
<value>testAdvisor2</value>
</list>
</property>
</bean>
</beans> public static void main(String[] args) {
FileSystemXmlApplicationContext ctx = new
FileSystemXmlApplicationContext("D:/workspace/demo_spring_standalone/src/main/resources/applicationContext-aop-proxy.xml");
TestTarget testTarget = (TestTarget) ctx.getBean("testAop");
testTarget.itest();
}源码分析
2.1 AOP初始化
TestTarget testTarget = (TestTarget) ctx.getBean("testAop");
上面这句代码看起来比较熟悉，没错，这句代码就是从spring上下文获取id=“testAop”的bean。从配置文件中看出，这是一个FactoryBean，这是spring专门设计为AOP服务的 ProxyFactoryBean，普通bean和FactoryBean的区别这里就不多说了。这里getBean方法直接会去调用getObject方法，这里跳过spring实例化bean的过程，直接进入到ProxyFactoryBean的方法getObject，
public Object getObject() throws BeansException {
initializeAdvisorChain();
if (isSingleton()) {
return getSingletonInstance();
}
else {
if (this.targetName == null) {
logger.warn("Using non-singleton proxies with singleton targets is often undesirable. " +
"Enable prototype proxies by setting the 'targetName' property.");
}
return newPrototypeInstance();
} private synchronized void initializeAdvisorChain() throws AopConfigException, BeansException {
//Advisor/Advice 链被初始化过的话，直接返回
if (this.advisorChainInitialized) {
return;
}
if (!ObjectUtils.isEmpty(this.interceptorNames)) {
// Materialize interceptor chain from bean names.
for (String name : this.interceptorNames) {
if (logger.isTraceEnabled()) {
logger.trace("Configuring advisor or advice '" + name + "'");
}
if (name.endsWith(GLOBAL_SUFFIX)) {
if (!(this.beanFactory instanceof ListableBeanFactory)) {
throw new AopConfigException(
"Can only use global advisors or interceptors with a ListableBeanFactory");
}
addGlobalAdvisor((ListableBeanFactory) this.beanFactory,
name.substring(0, name.length() - GLOBAL_SUFFIX.length()));
}
else {
// If we get here, we need to add a named interceptor.
// We must check if it's a singleton or prototype.
Object advice;
if (this.singleton || this.beanFactory.isSingleton(name)) {
// Add the real Advisor/Advice to the chain.
//这里又看到了熟悉的方法，没错获取advice bean对象
advice = this.beanFactory.getBean(name);
}
else {
// It's a prototype Advice or Advisor: replace with a prototype.
// Avoid unnecessary creation of prototype bean just for advisor chain initialization.
advice = new PrototypePlaceholderAdvisor(name);
}
addAdvisorOnChainCreation(advice, name);
}
}
}
this.advisorChainInitialized = true;
} private void addAdvisorOnChainCreation(Object next, String name) {
// We need to convert to an Advisor if necessary so that our source reference
// matches what we find from superclass interceptors.
Advisor advisor = namedBeanToAdvisor(next);
if (logger.isTraceEnabled()) {
logger.trace("Adding advisor with name '" + name + "'");
}
addAdvisor(advisor);
}advisors的类型是linkedList，这是一个advisor链，所有的advisor都放在这个链表里面。
private List<Advisor> advisors = new LinkedList<Advisor>(); public void addAdvisor(int pos, Advisor advisor) throws AopConfigException {
if (advisor instanceof IntroductionAdvisor) {
validateIntroductionAdvisor((IntroductionAdvisor) advisor);
}
addAdvisorInternal(pos, advisor);
}接下来继续看方法getObject下面的逻辑。
private synchronized Object getSingletonInstance() {
if (this.singletonInstance == null) {
//获取target bean的对象
this.targetSource = freshTargetSource();
if (this.autodetectInterfaces && getProxiedInterfaces().length == 0 && !isProxyTargetClass()) {
// Rely on AOP infrastructure to tell us what interfaces to proxy.
Class<?> targetClass = getTargetClass();
if (targetClass == null) {
throw new FactoryBeanNotInitializedException("Cannot determine target class for proxy");
}
//递归的获取目标类的及其父类的接口信息，并添加到AdvisedSupport的一个全局的列表中去
setInterfaces(ClassUtils.getAllInterfacesForClass(targetClass, this.proxyClassLoader));
}
// Initialize the shared singleton instance.
super.setFrozen(this.freezeProxy);
this.singletonInstance = getProxy(createAopProxy());
}
return this.singletonInstance;
} protected final synchronized AopProxy createAopProxy() {
if (!this.active) {
activate();
}
/*这里的方法getAopProxyFactory，得到的是DefaultAopProxyFactory，ProxyFactoryBean继承了ProxyCreatorSupport， *在ProxyCreatorSupport的构造函数中设置了的 this.aopProxyFactory = new DefaultAopProxyFactory(); *所以在实例化ProxyFactoryBean的时候就已经设置了这个aopProxyFactory */
return getAopProxyFactory().createAopProxy(this);
} /* * 这里写明了spring内部创建代理对象的两种方式： * （1）jdk动态代理：适用于目标类实现了接口，且目标方法在接口中有定义。 * （2）cglib动态代理，适用于目标类没有实现任何接口的情况。 */
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()) {
return new JdkDynamicAopProxy(config);
}
return new ObjenesisCglibAopProxy(config);
}
else {
return new JdkDynamicAopProxy(config);
}
} protected Object getProxy(AopProxy aopProxy) {
/*ProxyFactoryBean的getProxy方法，传入的参数是实际的proxy对象，也就是上一步创建的proxy， *也就是说实际调用的是具体的proxy对象的getProxy方法， */
return aopProxy.getProxy(this.proxyClassLoader);
} //这是jdk动态代理的方式
public Object getProxy(ClassLoader classLoader) {
if (logger.isDebugEnabled()) {
logger.debug("Creating JDK dynamic proxy: target source is " + this.advised.getTargetSource());
}
Class<?>[] proxiedInterfaces = AopProxyUtils.completeProxiedInterfaces(this.advised);
findDefinedEqualsAndHashCodeMethods(proxiedInterfaces);
return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);
} //这是cglib字节码增强的方式
public Object getProxy(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.
validateClassIfNecessary(proxySuperClass, classLoader);
// Configure CGLIB 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 UndeclaredThrowableStrategy(UndeclaredThrowableException.class));
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.
return createProxyClassAndInstance(enhancer, callbacks);
}
catch (CodeGenerationException ex) {
throw new AopConfigException("Could not generate CGLIB subclass of class [" +
this.advised.getTargetClass() + "]: " +
"Common causes of this problem include using a final class or a non-visible class",
ex);
}
catch (IllegalArgumentException ex) {
throw new AopConfigException("Could not generate CGLIB subclass of class [" +
this.advised.getTargetClass() + "]: " +
"Common causes of this problem include using a final class or a non-visible class",
ex);
}
catch (Exception ex) {
// TargetSource.getTarget() failed
throw new AopConfigException("Unexpected AOP exception", ex);
}
}2.2 切面（Advice）方法触发
testTarget.itest();testTarget是spring封装后的目标类的代理对象实例，在平常的spring AOP的使用中，咋看起来好像和这里的用法不太一样，这里是直接从上下文中直接获取封装后的bean对象
testAOP，而正常的spring AOP的使用中是使用aop标签在命令行中定义aop相关的元素，或者使用aop相关的注解，而且是直接调用目标方法，只要符合定义的aop切面的拦截规
则，该方法就会被拦截，并且织入advice逻辑。我们并没有去给目标对象生产代理，看似是这样的，其实封装代理这一步spring已经帮我们做了，也就是说我们运行程序的时候实际
上调用的是spring创建的目标对象的代理对象，只是创建代理对象这一步对用户来说是透明的。
下面我们看下相关的源码：
如果熟悉jdk动态代理的话，应该知道invoke方法，是通过jdk动态代理的方式实现代理需要重写的接口InvocationHandler的方法。
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { MethodInvocation invocation; Object oldProxy = null; boolean setProxyContext = false; TargetSource targetSource = this.advised.targetSource; Class<?> targetClass = null; Object target = null; try { if (!this.equalsDefined && AopUtils.isEqualsMethod(method)) { // The target does not implement the equals(Object) method itself. return equals(args[0]); } if (!this.hashCodeDefined && AopUtils.isHashCodeMethod(method)) { // The target does not implement the hashCode() method itself. return hashCode(); } 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;
if (this.advised.exposeProxy) { // Make invocation available if necessary. oldProxy = AopContext.setCurrentProxy(proxy); setProxyContext = true; }
// May be null. Get as late as possible to minimize the time we "own" the target,
// in case it comes from a pool.
target = targetSource.getTarget();
if (target != null) { targetClass = target.getClass(); }
// Get the interception chain for this method.
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. retVal = AopUtils.invokeJoinpointUsingReflection(target, method, args); }
else { // We need to create a method invocation... invocation = new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain); // Proceed to the joinpoint through the interceptor chain. retVal = invocation.proceed(); }
// Massage return value if necessary.
Class<?> returnType = method.getReturnType();
if (retVal != null && retVal == target && 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); }
}
} //当拦截器链为空的话，会调用方法AopUtils.invokeJoinpointUsingReflection，直接调用目标对象的目标方法
public static Object invokeJoinpointUsingReflection(Object target, Method method, Object[] args)
throws Throwable {
// Use reflection to invoke the method.
try {
ReflectionUtils.makeAccessible(method);
return method.invoke(target, args);
}
catch (InvocationTargetException ex) {
// Invoked method threw a checked exception.
// We must rethrow it. The client won't see the interceptor.
throw ex.getTargetException();
}
catch (IllegalArgumentException ex) {
throw new AopInvocationException("AOP configuration seems to be invalid: tried calling method [" +
method + "] on target [" + target + "]", ex);
}
catch (IllegalAccessException ex) {
throw new AopInvocationException("Could not access method [" + method + "]", ex);
}
}熟悉cglib动态代理的应该熟悉下面这个方法，方法intercept就是cglib方式实现动态代理时需要重写接口MethodInterceptor的方法。
public Object intercept(Object proxy, Method method, Object[] args, MethodProxy methodProxy) throws Throwable { Object oldProxy = null; boolean setProxyContext = false; Class<?> targetClass = null; Object target = null; try { if (this.advised.exposeProxy) { // Make invocation available if necessary. oldProxy = AopContext.setCurrentProxy(proxy); setProxyContext = true; } // May be null. Get as late as possible to minimize the time we // "own" the target, in case it comes from a pool... target = getTarget();
if (target != null) { targetClass = target.getClass(); }
//获取所有的拦截器及advice
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. retVal = methodProxy.invoke(target, args); } else { // We need to create a method invocation... retVal = new CglibMethodInvocation(proxy, target, method, args, targetClass, chain, methodProxy).proceed(); } retVal = processReturnType(proxy, target, method, retVal);
return retVal;
}
finally { if (target != null) { releaseTarget(target); }
if (setProxyContext) { // Restore old proxy. AopContext.setCurrentProxy(oldProxy); }
}
}如果你debug调试的话，代码会进入上面提到的两个方法之一（视目标类而定，如果目标类实现了接口且目标方法在接口中有定义，spring会使用jdk动态代理来实现代理，此时则会调用invoke方法；否则使用cglib来实现代理，则会调用intercept方法）。那到底为什么会调用这两个方法（或者到底什么原理才调用的这两个方法呢？），为了弄清楚这一点，这里使用ProxyGenerator来生成一个代理类对象，并把对象写到文件中，通过反编译工具查看生成的代码。
byte[] classFile = sun.misc.ProxyGenerator.generateProxyClass("$Proxy11", TestTarget.class.getInterfaces()); 这是生成的代理类的代码，可以看到把接口的方法全部重写了一遍（包括隐式继承的Object的方法toString,hashCode,equals）,最重要的是itest方法，也就是代理的目标方法。
import com.sjj.aop.TestInterface;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.lang.reflect.UndeclaredThrowableException;
public final class $Proxy11 extends Proxy implements TestInterface {
private static Method m1;
private static Method m0;
private static Method m3;
private static Method m2;
public $Proxy11(InvocationHandler paramInvocationHandler)
throws
{
super(paramInvocationHandler);
}
public final boolean equals(Object paramObject)
throws
{
try
{
return ((Boolean)this.h.invoke(this, m1, new Object[] { paramObject })).booleanValue();
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}
public final int hashCode()
throws
{
try
{
return ((Integer)this.h.invoke(this, m0, null)).intValue();
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}
public final void itest()
throws
{
try
{
/* * 这里调用了invoke方法，解释开始的疑问，cglib的方式应该与此类似 */
this.h.invoke(this, m3, null);
return;
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}
public final String toString()
throws
{
try
{
return (String)this.h.invoke(this, m2, null);
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}
static
{
try
{
m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[] { Class.forName("java.lang.Object") });
m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);
m3 = Class.forName("com.sjj.aop.TestInterface").getMethod("itest", new Class[0]);
m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
return;
}
catch (NoSuchMethodException localNoSuchMethodException)
{
throw new NoSuchMethodError(localNoSuchMethodException.getMessage());
}
catch (ClassNotFoundException localClassNotFoundException)
{
throw new NoClassDefFoundError(localClassNotFoundException.getMessage());
}
}
}
最终会调用到DefaultAdvisorChainFactory的getInterceptorsAndDynamicInterceptionAdvice
public List<Object> getInterceptorsAndDynamicInterceptionAdvice(
Advised config, Method method, Class<?> targetClass) {
// This is somewhat tricky... We have to process introductions first,
// but we need to preserve order in the ultimate list.
List<Object> interceptorList = new ArrayList<Object>(config.getAdvisors().length);
Class<?> actualClass = (targetClass != null ? targetClass : method.getDeclaringClass());
boolean hasIntroductions = hasMatchingIntroductions(config, actualClass);
/* *这里的GlobalAdvisorAdapterRegistry使用了单例的设计模式，具体可参考其源码 *采用饿汉模式直接创建了一个DefaultAdvisorAdapterRegistry对象,并把三种类型的拦截器注册进去 *具体内容参考DefaultAdvisorAdapterRegistry的构造方法 */
AdvisorAdapterRegistry registry = GlobalAdvisorAdapterRegistry.getInstance();
for (Advisor advisor : config.getAdvisors()) {
if (advisor instanceof PointcutAdvisor) {
// Add it conditionally.
PointcutAdvisor pointcutAdvisor = (PointcutAdvisor) advisor;
if (config.isPreFiltered() || pointcutAdvisor.getPointcut().getClassFilter().matches(actualClass)) {
/*根据advisor关联的advice的类型，为advice创建相应的Interceptor, *AfterReturningAdviceAdapter --- AfterReturningAdviceInterceptor *MethodBeforeAdviceAdapter --- MethodBeforeAdviceInterceptor *ThrowsAdviceAdapter --- ThrowsAdviceInterceptor */
MethodInterceptor[] interceptors = registry.getInterceptors(advisor);
MethodMatcher mm = pointcutAdvisor.getPointcut().getMethodMatcher();
//根据方法的签名和advisor的拦截规则判断方法method是否需要拦截，如果需要则把advisor下的所有advice添加到拦截器列表里去
if (MethodMatchers.matches(mm, method, actualClass, hasIntroductions)) {
if (mm.isRuntime()) {
// Creating a new object instance in the getInterceptors() method
// isn't a problem as we normally cache created chains.
for (MethodInterceptor interceptor : interceptors) {
interceptorList.add(new InterceptorAndDynamicMethodMatcher(interceptor, mm));
}
}
else {
interceptorList.addAll(Arrays.asList(interceptors));
}
}
}
}
else if (advisor instanceof IntroductionAdvisor) {
IntroductionAdvisor ia = (IntroductionAdvisor) advisor;
if (config.isPreFiltered() || ia.getClassFilter().matches(actualClass)) {
Interceptor[] interceptors = registry.getInterceptors(advisor);
interceptorList.addAll(Arrays.asList(interceptors));
}
}
else {
Interceptor[] interceptors = registry.getInterceptors(advisor);
interceptorList.addAll(Arrays.asList(interceptors));
}
}
return interceptorList;
}public abstract class GlobalAdvisorAdapterRegistry {
/** * Keep track of a single instance so we can return it to classes that request it. */
private static AdvisorAdapterRegistry instance = new DefaultAdvisorAdapterRegistry();
/** * Return the singleton {@link DefaultAdvisorAdapterRegistry} instance. */
public static AdvisorAdapterRegistry getInstance() {
return instance;
}
/** * Reset the singleton {@link DefaultAdvisorAdapterRegistry}, removing any * {@link AdvisorAdapterRegistry#registerAdvisorAdapter(AdvisorAdapter) registered} * adapters. */
static void reset() {
instance = new DefaultAdvisorAdapterRegistry();
}
}public class DefaultAdvisorAdapterRegistry implements AdvisorAdapterRegistry, Serializable {
private final List<AdvisorAdapter> adapters = new ArrayList<AdvisorAdapter>(3);
/** * Create a new DefaultAdvisorAdapterRegistry, registering well-known adapters. */
public DefaultAdvisorAdapterRegistry() {
registerAdvisorAdapter(new MethodBeforeAdviceAdapter());
registerAdvisorAdapter(new AfterReturningAdviceAdapter());
registerAdvisorAdapter(new ThrowsAdviceAdapter());
}CglibMethodInvocation是CglibAopProxy的内部类，继承了ReflectiveMethodInvocation，下面看下其proceed方法：
public Object proceed() throws Throwable {
// We start with an index of -1 and increment early.
//当遍历完整个拦截器链时，代码进入这个分支，主要功能是调用真正的目标方法
if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) {
return invokeJoinpoint();
}
/* * 这里interceptorsAndDynamicMethodMatchers和currentInterceptorIndex都是全局变量， * 这样设计的巧妙之处就在于，当具体的interceptor里的invoke方法递归调用这里proceed方法的时候， * 其实是对拦截器链做顺序访问，即依次调用拦截器链里的拦截器。 */
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.
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.
// 如果拦截器和方法不匹配，则递归调用proceed方法，遍历拦截器链
return proceed();
}
}
else {
// It's an interceptor, so we just invoke it: The pointcut will have
// been evaluated statically before this object was constructed.
/*这里的设计比较巧妙，把当前对象作为参数传进去，这样在相应的Interceptor的invoke方法里就可以递归调用 *proceed方法，从而达到遍历拦截器链的目的 */
return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);
}
} /* *这是AfterReturningAdviceInterceptor的invoke方法，注意看两者调用proceed方法、advice方法（before、afterReturning）的顺序 */
public Object invoke(MethodInvocation mi) throws Throwable {
// 这里调用proceed方法，而不是目标方法，这样可以递归调用整个拦截器链的拦截器
Object retVal = mi.proceed();
this.advice.afterReturning(retVal, mi.getMethod(), mi.getArguments(), mi.getThis());
return retVal;
} /* *这是MethodBeforeAdviceInterceptor的invoke方法 */
public Object invoke(MethodInvocation mi) throws Throwable {
this.advice.before(mi.getMethod(), mi.getArguments(), mi.getThis() );
// 这里调用proceed方法，而不是目标方法，这样可以递归调用整个拦截器链的拦截器
return mi.proceed();
} protected Object invokeJoinpoint() throws Throwable {
if (this.publicMethod) {
//调用真正的目标方法，在整个拦截器链最后才调用这个方法
return this.methodProxy.invoke(this.target, this.arguments);
}
else {
return super.invokeJoinpoint();
}
}- 之前对spring一直停留在用的层面，知道springAOP是通过动态代理实现，动态代理有两种实现方式：jdk dynamic proxy和cglib字节码增强，但并不知道具体的实
现细节，分析了AOP的实现源码之后才对如何使用者两种方式实现动态代理以及AOP的实现细节有了清晰的认识。
