写在前面
在分析 Spring AOP 源码之前，如果你对 Spring IOC、依赖注入(DI) 原理不是很清楚，建议您先了解一下：Spring IOC 源码解析、Spring 依赖注入(DI) 源码解析，这样或许会让你的思路更加清晰。
1.什么是Spring AOP ？
AOP（Aspect Oriented Programming）即：面向切面编程，通过预编译方式和运行期间动态代理实现程序功能的统一维护的一种技术，是OOP(面向对象编程)的延续。
AOP是通过动态代理方式，从而实现在不修改源码的情况下，给程序动态的添加功能的一种技术。AOP，最主要的目的就是完成解耦。
2.AOP 名词介绍
在AOP中，共涉及到1.切面 Aspect、2.连接点 JoinPoint、3.通知 Advice、4.切入点 Pointcut、5.目标对象 Target Object这 5 个名词。
AOP 名词介绍，这块不做介绍。如果你想要了解，请跳转链接充电：AOP 名词介绍
3.AOP 通知Advice 介绍
AOP 通知，共有1.前置通知 Before advice、2.后置通知 After advice、3.返回后通知 After return advice、4.抛出异常后通知 After throwing advice、5、环绕通知 Around advice这 5 个。
AOP 通知相关知识，这块也不做介绍。如果你想要了解，请跳转链接充电：AOP 通知 Advice 介绍
4.AOP 在项目中的使用
AOP 在项目中的使用，此处分1.xml配置和 2.注解配置 分开进行介绍。AOP 在项目中的使用，我在之前博客中也有介绍，此处不再赘余。请跳转至：Spring AOP 在项目中的使用 去了解。本文主要来分析 Spring AOP 的源码部分。
5.AOP 源码分析从何入手
在 Spring 中，使用最多的就是工厂方法模式。我们在分析 Spring IOC & DI 依赖注入时，是从 BeanFactory 接口开始，然后通过getBean() 方法入手；
显然 Spring AOP 的实现，也使用了工厂方法模式。我们在 ProxyFactory 类中，可以通过 getProxy() 方法来获取 Spring 帮我们生成的 Bean 实例的代理对象。
源码解析阶段，会涉及到动态代理，如过你对 JDK动态代理 和 Cglib 代理还不是很了解，你可以点击如下链接了解：①JDK动态代理（Dynamic Proxy） ②Cglib动态代理（Cglib Proxy）
6.Spring AOP 源码分析时序图 单击放大查看(高清图下载请转至文末链接)
7.AOP 源码分析
7.1 JDK 动态代理
1.创建代理对象
@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);
//调用Proxy.newProxyInstance创建代理对象
return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);
}
2.执行 invoke() 方法
@Override
@Nullable
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
MethodInvocation invocation;
Object oldProxy = null;
boolean setProxyContext = false;
TargetSource targetSource = this.advised.targetSource;
Object target = null;
try {
//eqauls()方法判断
if (!this.equalsDefined && AopUtils.isEqualsMethod(method)) {
// The target does not implement the equals(Object) method itself.
return equals(args[0]);
}
//hashCode()方法方法判断
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);
}
//Advised接口或者其父接口中定义的方法,直接反射调用,不应用通知
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;
if (this.advised.exposeProxy) {
// Make invocation available if necessary.
oldProxy = AopContext.setCurrentProxy(proxy);
setProxyContext = true;
}
//获得目标对象的类
target = targetSource.getTarget();
Class<?> targetClass = (target != null ? target.getClass() : null);
//此处作通知(拦截器链)
//获取可以应用到此方法上的Interceptor列表(拦截器链，为环绕通知做准备)
List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);
//如果没有可以应用到此方法的通知(Interceptor)，此直接反射调用 method.invoke(target, args)
if (chain.isEmpty()) {
Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
retVal = AopUtils.invokeJoinpointUsingReflection(target, method, argsToUse);
}else {
//创建MethodInvocation
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 != Object.class && returnType.isInstance(proxy) &&
!RawTargetAccess.class.isAssignableFrom(method.getDeclaringClass())) {
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);
}
}
}
3.生成拦截器链 chain
/**
* 从提供的配置实例config中获取advisor列表,遍历处理这些advisor.如果是IntroductionAdvisor,
* 则判断此Advisor能否应用到目标类targetClass上.如果是PointcutAdvisor,则判断
* 此Advisor能否应用到目标方法method上.将满足条件的Advisor通过AdvisorAdaptor转化成Interceptor列表返回.
*/
@Override
public List<Object> getInterceptorsAndDynamicInterceptionAdvice(
Advised config, Method method, @Nullable 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<>(config.getAdvisors().length);
Class<?> actualClass = (targetClass != null ? targetClass : method.getDeclaringClass());
//查看是否包含IntroductionAdvisor
boolean hasIntroductions = hasMatchingIntroductions(config, actualClass);
//这里实际上注册一系列AdvisorAdapter,用于将Advisor转化成MethodInterceptor
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)) {
//这个地方这两个方法的位置可以互换下
//将Advisor转化成Interceptor(此处为方法拦截器，即AOP中的切点，就是我们编写的每一个Method)
MethodInterceptor[] interceptors = registry.getInterceptors(advisor);
//检查当前advisor的pointcut是否可以匹配当前方法
MethodMatcher mm = pointcutAdvisor.getPointcut().getMethodMatcher();
//在此处，根据你的配置，确定该在哪个阶段进行通知。
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;
}
4.通过拦截器链进入连接点，开始执行proceed()方法
@Override
@Nullable
public Object proceed() throws Throwable {
// We start with an index of -1 and increment early.
//如果Interceptor执行完了，则执行joinPoint
if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) {
return invokeJoinpoint();
}
Object interceptorOrInterceptionAdvice =
this.interceptorsAndDynamicMethodMatchers.get(++this.currentInterceptorIndex);
//如果要动态匹配joinPoint
if (interceptorOrInterceptionAdvice instanceof InterceptorAndDynamicMethodMatcher) {
// Evaluate dynamic method matcher here: static part will already have
// been evaluated and found to match.
InterceptorAndDynamicMethodMatcher dm =
(InterceptorAndDynamicMethodMatcher) interceptorOrInterceptionAdvice;
//动态匹配：运行时参数是否满足匹配条件
if (dm.methodMatcher.matches(this.method, this.targetClass, this.arguments)) {
//通过 invoke()方法，执行当前的拦截器 Interceptor
return dm.interceptor.invoke(this);
}
else {
// Dynamic matching failed.
// Skip this interceptor and invoke the next in the chain.
//动态匹配失败时,略过当前Intercetpor,调用下一个Interceptor
return proceed();
}
}
else {
// It's an interceptor, so we just invoke it: The pointcut will have
// been evaluated statically before this object was constructed.
//执行当前Intercetpor
return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);
}
}
7.2 Cglib 动态代理
1.创建代理对象
@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.
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 ClassLoaderAwareUndeclaredThrowableStrategy(classLoader));
//1.通过 getCallbacks() 回调生成拦截器链，并执行 proceed() 方法，去执行 Interceptor
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 | 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 (Throwable ex) {
// TargetSource.getTarget() failed
throw new AopConfigException("Unexpected AOP exception", ex);
}
}
2.调用 getCallbacks()方法
private Callback[] getCallbacks(Class<?> rootClass) throws Exception {
// Parameters used for optimization choices...
boolean exposeProxy = this.advised.isExposeProxy();
boolean isFrozen = this.advised.isFrozen();
boolean isStatic = this.advised.getTargetSource().isStatic();
// Choose an "aop" interceptor (used for AOP calls).
//2.创建了一个 aopInterceptor 拦截器
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[] {
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;
}
3.通过内部类的方式，调用重写的 intercept()方法
/**
* General purpose AOP callback. Used when the target is dynamic or when the
* proxy is not frozen.
*/
private static class DynamicAdvisedInterceptor implements MethodInterceptor, Serializable {
private final AdvisedSupport advised;
public DynamicAdvisedInterceptor(AdvisedSupport advised) {
this.advised = advised;
}
@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...
//获得目标对象的类
target = targetSource.getTarget();
Class<?> targetClass = (target != null ? target.getClass() : null);
List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);
Object retVal;
//如果没有可以应用到此方法的通知(Interceptor)，此直接反射调用 method.invoke(target, args)
if (chain.isEmpty() && Modifier.isPublic(method.getModifiers())) {
Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
retVal = methodProxy.invoke(target, argsToUse);
}
else {
// We need to create a method invocation...
//创建MethodInvocation,匹配joinPoint，调用 proceed()方法执行
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);
}
}
}
......
}
4.调用 proceed() 方法
此处 proceed() 方法，同 JDK动态代理 proceed()，两者都是调用同一个 proceed()完成最终操作。
8.AOP 拦截器链图形化
AOP其实通过动态代理的方式来操作MethodInterceptor拦截器链，根据方法器链中的内容来做出相关操作。
如果整个链路下，只有一个拦截器，则它会执行自己；如果是多个拦截器，则是一个拦截器链，便会一个一个全部执行完(拦截器链中保存的就是Before、After、AfterReturn等配置的信息)
至此，AOP分别使用JDK动态代理和Cglib代理的源码分析，到此就结束了。源码解析，建议你按照 6.Spring AOP 源码分析时序图 ，打开源码自己一步步分析，这样会让你对它的执行过程更加清晰。附 spring-framework-5.0.2.RELEASE （中文注释）版本，直接解压 IDEA 打开即可。
地址： 1.spring-framework-5.0.2.RELEASE (中文注释)版本
2.网盘地址：spring-framework-5.0.2.RELEASE (中文注释)版本(提取码：uck4 )
恭喜您，枯燥源码看到这里。Spring AOP 相对简单，就先介绍到此
如果本文对你有所帮助，那就给我点个赞呗 ^ _ ^
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