上回文我们说道不同场景使用不同的aop逻辑判断,本章节我们分别看使用JDK动态代理和cglib进行代理有什么区别
先看JDK动态代理的方式是如何实现aop的
JdkDynamicAopProxy类图.png
从UML类图可以看到,JdkDynamicAopProxy实现了AopProxy和InvocationHandler接口
我们跟踪getProxy()方法
@Override
public Object getProxy() {
return getProxy(ClassUtils.getDefaultClassLoader());
}
@Override
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, true);
findDefinedEqualsAndHashCodeMethods(proxiedInterfaces);
return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);
}
看到了非常熟悉的Proxy.newProxyInstance(classLoader, proxiedInterfaces, this)代码
那么实现aop核心的逻辑就是在实现InvocationHandler的invoke()中
/**
* Implementation of {@code InvocationHandler.invoke}.
* <p>Callers will see exactly the exception thrown by the target,
* unless a hook method throws an exception.
*/
@Override
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]);
}
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;
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.
Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
retVal = AopUtils.invokeJoinpointUsingReflection(target, method, argsToUse);
}
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 != 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);
}
}
}
在真正分析上面代码之前,分享一个面试题,假如在Service类中方法A 定义了事务,方法B也定义了事务,那么在方法A中直接this.B()调用B方法,B方法的事务可以生效吗
我们知道Spring事务是基于aop实现的
前面我们已经分析到aop的原理是底层进行了代理,所以如果直接this.B()方法 是无法生效的,如果不理解,等我们全部撸完这部分代码就知道了原因了
那么如何能进行生效呢,上面部分代码给出了答案
首先我们要设置<expose-proxy />配置 暴露代理类,然后通过AopContext.getCurrentProxy.B()方法即可
好了,我们继续探讨JDK动态代理实现aop
其中关键2个步骤为
1.获取拦截器执行链
List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);
/**
* Determine a list of {@link org.aopalliance.intercept.MethodInterceptor} objects
* for the given method, based on this configuration.
* @param method the proxied method
* @param targetClass the target class
* @return a List of MethodInterceptors (may also include InterceptorAndDynamicMethodMatchers)
*/
public List<Object> getInterceptorsAndDynamicInterceptionAdvice(Method method, Class<?> targetClass) {
MethodCacheKey cacheKey = new MethodCacheKey(method);
List<Object> cached = this.methodCache.get(cacheKey);
if (cached == null) {
cached = this.advisorChainFactory.getInterceptorsAndDynamicInterceptionAdvice(
this, method, targetClass);
this.methodCache.put(cacheKey, cached);
}
return cached;
}
@Override
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);
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)) {
MethodMatcher mm = pointcutAdvisor.getPointcut().getMethodMatcher();
if (MethodMatchers.matches(mm, method, actualClass, hasIntroductions)) {
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) {
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;
}
可以看到以上代码有3部分逻辑将advisor 分为普通的增强器,引介型增强器,还有普通的Interceptor拦截器
我们主要关注advisor 为PointcutAdvisor时,将Advisor中的beforeAdvice,afterReturningAdvice通知通过适配器转换成MethodInterceptor,剩下3个AbstractAspectAdvice的实现，直接实现了MethodInterceptor，所以不需要适配，至于为什么没有统一我也不得而知
MethodInterceptor[] interceptors = registry.getInterceptors(advisor);
@Override
public MethodInterceptor[] getInterceptors(Advisor advisor) throws UnknownAdviceTypeException {
List<MethodInterceptor> interceptors = new ArrayList<>(3);
Advice advice = advisor.getAdvice();
if (advice instanceof MethodInterceptor) {
interceptors.add((MethodInterceptor) advice);
}
for (AdvisorAdapter adapter : this.adapters) {
if (adapter.supportsAdvice(advice)) {
interceptors.add(adapter.getInterceptor(advisor));
}
}
if (interceptors.isEmpty()) {
throw new UnknownAdviceTypeException(advisor.getAdvice());
}
return interceptors.toArray(new MethodInterceptor[0]);
}
回到刚才的getInterceptorsAndDynamicInterceptionAdvice()方法,后面便将MethodInterceptor 转换为InterceptorAndDynamicMethodMatcher.所以在invoke()方法中getInterceptorsAndDynamicInterceptionAdvice()便返回了拦截器执行链，若该拦截器执行链为空，则直接通过反射调用目标方法，否则则将拦截器执行链转换为ReflectiveMethodInvocation对象
* Construct a new ReflectiveMethodInvocation with the given arguments.
* @param proxy the proxy object that the invocation was made on
* @param target the target object to invoke
* @param method the method to invoke
* @param arguments the arguments to invoke the method with
* @param targetClass the target class, for MethodMatcher invocations
* @param interceptorsAndDynamicMethodMatchers interceptors that should be applied,
* along with any InterceptorAndDynamicMethodMatchers that need evaluation at runtime.
* MethodMatchers included in this struct must already have been found to have matched
* as far as was possibly statically. Passing an array might be about 10% faster,
* but would complicate the code. And it would work only for static pointcuts.
*/
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;
}
我们可以简单的理解拦截器执行链+本身的Method = ReflectiveMethodInvocation 方法调用链
@Override
@Nullable
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.
InterceptorAndDynamicMethodMatcher dm =
(InterceptorAndDynamicMethodMatcher) interceptorOrInterceptionAdvice;
Class<?> targetClass = (this.targetClass != null ? this.targetClass : this.method.getDeclaringClass());
// 匹配成功，则进行执行链的调用
if (dm.methodMatcher.matches(this.method, targetClass, this.arguments)) {
return dm.interceptor.invoke(this);
}
else {
// 执行链向下进行
// Dynamic matching failed.
// Skip this interceptor and invoke the next in the chain.
return proceed();
}
}
else {
// It's an interceptor, so we just invoke it: The pointcut will have
// been evaluated statically before this object was constructed.
return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);
}
}
可以很清楚的看到，ReflectiveMethodInvocation的proceed()方法便是aop执行拦截的核心原理，具体实现为ReflectiveMethodInvocation对象中维护一个拦截器执行链执行的index位置计数器，记录着当前调用链的位置，以便链可以有序地进行下去，每个链执行的内部逻辑则由各个MethodInterceptor进行不同的实现。JDK动态动态代理实现aop就分析到这，下面说说cglib的实现
@Override
public 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...
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));
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 " + 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);
}
}
可以看到通过Callback[] callbacks = getCallbacks(rootClass)方法获取到的调用链
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).
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;
}
Callback aopInterceptor = new DynamicAdvisedInterceptor(this.advised);方法可以看到将AdvisedSupport封装成了DynamicAdvisedInterceptor，继而添加到了Callback调用链中，所以该实现的核心就在DynamicAdvisedInterceptor中，该类实现了MethodInterceptor接口，所以我继续跟踪intercept方法（注意这里的MethodInterceptor与上面JDK动态代理实现aop的 MethodInterceptor 不是同一个类），
@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);
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);
retVal = methodProxy.invoke(target, argsToUse);
}
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 && !targetSource.isStatic()) {
targetSource.releaseTarget(target);
}
if (setProxyContext) {
// Restore old proxy.
AopContext.setCurrentProxy(oldProxy);
}
}
}
可以看到核心逻辑List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);
new CglibMethodInvocation(proxy, target, method, args, targetClass, chain, methodProxy).proceed();
getInterceptorsAndDynamicInterceptionAdvice方法则是复用了AdvisedSupport中的该方法，而CglibMethodInvocation任务执行链则继承了ReflectiveMethodInvocation类，且并未改写proceed()方法，所以执行逻辑不再赘述。
至此动态aop的2种实现方式都已分析完成，希望你能有所收获，
鉴于本人水平有限，文中若有错误欢迎批评指正。
原创不易，若有转载请注明来源。
