Spring AOP源码目录
Spring AOP源码01：Jdk动态代理底层源码
Spring AOP源码02：ProxyFactory
Spring AOP源码03：JdkDynamicAopProxy
Spring AOP源码04：MethodInvocation 拦截器调用
Spring AOP源码05：DefaultAdvisorAutoProxyCreator
Spring期末考压轴题：当Spring AOP遇上循环依赖
git注释源码地址：https://github.com/chaitou/spring-framework-master.git
前言
如下图，结合第二篇Spring AOP核心源码 ProxyFactory，Spring AOP动态代理有2中生成方式，当代理对象实现了接口且没有配置强制使用cglib代理时，将使用JdkDynamicAopProxy生成代理。反之使用CglibAopProxy生成代理。同时我们在第一篇Jdk动态代理底层源码中已知，Jdk动态代理通过getProxy生成代理，同时$proxy代理对象在调用方法时，将会回调invoke方法进行。因此对于JdkDynamicAopProxy来说，最重要的代码就是分析getProxy和invoke方法。至于生成代理的底层源码，第一篇已经介绍过，这里不再赘述
源码分析
getProxy
下面代码在第一篇Jdk动态代理底层源码中我们手动写过一遍，这里再复习一下
@Override
public Object getProxy(@Nullable ClassLoader classLoader) {
if (logger.isTraceEnabled()) {
logger.trace("Creating JDK dynamic proxy: " + this.advised.getTargetSource());
}
// 获取代理接口
Class<?>[] proxiedInterfaces = AopProxyUtils.completeProxiedInterfaces(this.advised, true);
// 判断接口是否又hashCode和equals方法
findDefinedEqualsAndHashCodeMethods(proxiedInterfaces);
// 使用JDK代理(classLoader, 接口, 当前JdkDynamicAopProxy对象：用于回调invoke和target对象方法)
return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);
}
classLoader：当前类加载器proxiedInterfaces：当前代理类所实现的接口数组this：将自身类对象传给生成的代理，作为代理的属性h，属性h将被用于方法回调触发h.invoke方法，实现增强
invoke
在开始invoke之前，先定一下目标，为了抓住主干，本专题只关心普通增强，引介增强等将暂时跳过，另外独立出章节详解，因此遇到引介增强等可以暂时先不纠结
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
Object oldProxy = null;
boolean setProxyContext = false;
// 获取代理目标对象
TargetSource targetSource = this.advised.targetSource;
Object target = null;
try {
// equals方法处理
if (!this.equalsDefined && AopUtils.isEqualsMethod(method)) {
// The target does not implement the equals(Object) method itself.
return equals(args[0]);
}
// hashCode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);
}
// Advised接口或者其父接口中定义的方法,直接反射调用
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;
// 目标对象内部调用是无法实现增强的，如果exposeProxy设置为true，需要暴露代理
// ThreadLocal<Object> currentProxy
// 对象是ThreadLocal，在finally后会清除currentProxy
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.
// 以防target来自对象池，所以在创建代理前调用get获取target
target = targetSource.getTarget();
Class<?> targetClass = (target != null ? target.getClass() : null);
// Get the interception chain for this method.
// 1. 获取拦截器链
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.
// 拦截器为空，直接调用切点方法
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.
Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
retVal = AopUtils.invokeJoinpointUsingReflection(target, method, argsToUse);
}
else {
// We need to create a method invocation...
// 2. 将拦截器统一封装成ReflectiveMethodInvocation
MethodInvocation invocation =
new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain);
// Proceed to the joinpoint through the interceptor chain.
// 3. 执行拦截器链
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())) {
// 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.
// 如果自定义了TargetSource，释放target资源池由子类实现
targetSource.releaseTarget(target);
}
if (setProxyContext) {
// Restore old proxy.
AopContext.setCurrentProxy(oldProxy);
}
}
}
1. 获取拦截器链
该方法将获取到所有与当前method匹配的advice(增强)，跟踪getInterceptorsAndDynamicInterceptionAdvice代码，发现Spring AOP也使用缓存进行提高性能，如果该方法已经获取过拦截器，则直接取缓存，否则通过advisorChainFactory获取拦截器链
public List<Object> getInterceptorsAndDynamicInterceptionAdvice(Method method, @Nullable Class<?> targetClass) {
MethodCacheKey cacheKey = new MethodCacheKey(method);
// 从缓存中获取
List<Object> cached = this.methodCache.get(cacheKey);
if (cached == null) {
// 获取拦截器链
cached = this.advisorChainFactory.getInterceptorsAndDynamicInterceptionAdvice(
this, method, targetClass);
// 设置缓存
this.methodCache.put(cacheKey, cached);
}
return cached;
}
继续跟中getInterceptorsAndDynamicInterceptionAdvice方法
// DefaultAdvisorChainFactory.java
public class DefaultAdvisorChainFactory implements AdvisorChainFactory, Serializable {
@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.
AdvisorAdapterRegistry registry = GlobalAdvisorAdapterRegistry.getInstance();
Advisor[] advisors = config.getAdvisors();
List<Object> interceptorList = new ArrayList<>(advisors.length);
Class<?> actualClass = (targetClass != null ? targetClass : method.getDeclaringClass());
Boolean hasIntroductions = null;
// 循环所有切面
for (Advisor advisor : advisors) {
if (advisor instanceof PointcutAdvisor) {
// Add it conditionally.
PointcutAdvisor pointcutAdvisor = (PointcutAdvisor) advisor;
// 校验当前Advisor是否适用于当前对象
if (config.isPreFiltered() || pointcutAdvisor.getPointcut().getClassFilter().matches(actualClass)) {
MethodMatcher mm = pointcutAdvisor.getPointcut().getMethodMatcher();
boolean match;
// 校验Advisor是否应用到当前方法上
if (mm instanceof IntroductionAwareMethodMatcher) {
if (hasIntroductions == null) {
hasIntroductions = hasMatchingIntroductions(advisors, actualClass);
}
match = ((IntroductionAwareMethodMatcher) mm).matches(method, actualClass, hasIntroductions);
}
else {
match = mm.matches(method, actualClass);
}
// 匹配成功
if (match) {
// 从advisor中获取拦截器数组
MethodInterceptor[] interceptors = registry.getInterceptors(advisor);
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) {
// 添加动态拦截器
interceptorList.add(new InterceptorAndDynamicMethodMatcher(interceptor, mm));
}
}
else {
// 添加普通拦截器
interceptorList.addAll(Arrays.asList(interceptors));
}
}
}
}
// 引介增强
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));
}
}
// 其他类型的advisor
else {
Interceptor[] interceptors = registry.getInterceptors(advisor);
interceptorList.addAll(Arrays.asList(interceptors));
}
}
return interceptorList;
}
...
}
剖去引介增强，动态增强，我们只关心普通拦截器。整个代码思路还是比较清晰的，获取所有Advisor(切面)，通过pointcutAdvisor.getPointcut().getClassFilter().matches(actualClass)校验当前代理对象是否匹配该Advisor，再通过pointcutAdvisor.getPointcut().getMethodMatcher()校验是否匹配当前调用method。如果通过校验，则提取advisor中的interceptors拦截器，添加到interceptorList中
2. 将拦截器封装成ReflectiveMethodInvocation
一个构造器的调用，重点在下一步调用
protected ReflectiveMethodInvocation(
Object proxy, @Nullable Object target, Method method, @Nullable Object[] arguments,
@Nullable Class<?> targetClass, List<Object> interceptorsAndDynamicMethodMatchers) {
this.proxy = proxy;
this.target = target;
this.targetClass = targetClass;
this.method = BridgeMethodResolver.findBridgedMethod(method);
this.arguments = AopProxyUtils.adaptArgumentsIfNecessary(method, arguments);
this.interceptorsAndDynamicMethodMatchers = interceptorsAndDynamicMethodMatchers;
}
3. 执行拦截器链
// 执行拦截器链
retVal = invocation.proceed();
public Object proceed() throws Throwable {
// We start with an index of -1 and increment early.
if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) {
return invokeJoinpoint();
}
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;
Class<?> targetClass = (this.targetClass != null ? this.targetClass : this.method.getDeclaringClass());
if (dm.methodMatcher.matches(this.method, 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，则跳过
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，直接触发
return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);
}
}
同样我们只关心普通拦截器，但是看到普通拦截器仅仅只有一行代码
return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);
这一行代码就可以让拦截器按照Before、After甚至是用户自定义的Order顺序进行链式调用，这也太神奇了吧？下一节我们将挑出AspectJAfterAdvice和MethodBeforeAdviceInterceptor探究拦截器是如何实现增强与method之前的有序调用
