关键词:
Spring AOP的面向切面编程,是面向对象编程的一种补充,用于处理系统中分布的各个模块的横切关注点,比如说事务管理、日志、缓存等。它是使用动态代理实现的,在内存中临时为方法生成一个AOP对象,这个对象包含目标对象的所有方法,在特定的切点做了增强处理,并回调原来的方法。
Spring AOP的动态代理主要有两种方式实现,JDK动态代理和cglib动态代理。JDK动态代理通过反射来接收被代理的类,但是被代理的类必须实现接口,核心是InvocationHandler和Proxy类。cglib动态代理的类一般是没有实现接口的类,cglib是一个代码生成的类库,可以在运行时动态生成某个类的子类,所以,CGLIB是通过继承的方式做的动态代理,因此如果某个类被标记为final,那么它是无法使用CGLIB做动态代理的。
AOP实现中,可以看到三个主要的步骤,一个是代理对象的生成,然后是拦截器的作用,然后是Aspect编织的实现。
ProxyFactoryBean生成AopProxy
ProxyFactoryBean生成AOP proxy
1 /** 2 * Return a proxy. Invoked when clients obtain beans from this factory bean. 3 * Create an instance of the AOP proxy to be returned by this factory. 4 * The instance will be cached for a singleton, and create on each call to 5 * <code>getObject()</code> for a proxy. 6 * @return a fresh AOP proxy reflecting the current state of this factory 7 */ 8 public Object getObject() throws BeansException 9 initializeAdvisorChain(); 10 if (isSingleton()) 11 return getSingletonInstance(); 12 13 else 14 if (this.targetName == null) 15 logger.warn("Using non-singleton proxies with singleton targets is often undesirable. " + 16 "Enable prototype proxies by setting the ‘targetName‘ property."); 17 18 return newPrototypeInstance(); 19 20
初始化Advisor chain
1 /** 2 * Create the advisor (interceptor) chain. Aadvisors that are sourced 3 * from a BeanFactory will be refreshed each time a new prototype instance 4 * is added. Interceptors added programmatically through the factory API 5 * are unaffected by such changes. 6 */ 7 private synchronized void initializeAdvisorChain() throws AopConfigException, BeansException 8 if (this.advisorChainInitialized) 9 return; 10 11 12 if (!ObjectUtils.isEmpty(this.interceptorNames)) 13 if (this.beanFactory == null) 14 throw new IllegalStateException("No BeanFactory available anymore (probably due to serialization) " + 15 "- cannot resolve interceptor names " + Arrays.asList(this.interceptorNames)); 16 17 18 // Globals can‘t be last unless we specified a targetSource using the property... 19 if (this.interceptorNames[this.interceptorNames.length - 1].endsWith(GLOBAL_SUFFIX) && 20 this.targetName == null && this.targetSource == EMPTY_TARGET_SOURCE) 21 throw new AopConfigException("Target required after globals"); 22 23 24 // Materialize interceptor chain from bean names. 25 for (int i = 0; i < this.interceptorNames.length; i++) 26 String name = this.interceptorNames[i]; 27 if (logger.isTraceEnabled()) 28 logger.trace("Configuring advisor or advice ‘" + name + "‘"); 29 30 31 if (name.endsWith(GLOBAL_SUFFIX)) 32 if (!(this.beanFactory instanceof ListableBeanFactory)) 33 throw new AopConfigException( 34 "Can only use global advisors or interceptors with a ListableBeanFactory"); 35 36 addGlobalAdvisor((ListableBeanFactory) this.beanFactory, 37 name.substring(0, name.length() - GLOBAL_SUFFIX.length())); 38 39 40 else 41 // If we get here, we need to add a named interceptor. 42 // We must check if it‘s a singleton or prototype. 43 Object advice = null; 44 if (this.singleton || this.beanFactory.isSingleton(this.interceptorNames[i])) 45 // Add the real Advisor/Advice to the chain. 46 advice = this.beanFactory.getBean(this.interceptorNames[i]); 47 48 else 49 // It‘s a prototype Advice or Advisor: replace with a prototype. 50 // Avoid unnecessary creation of prototype bean just for advisor chain initialization. 51 advice = new PrototypePlaceholderAdvisor(this.interceptorNames[i]); 52 53 addAdvisorOnChainCreation(advice, this.interceptorNames[i]); 54 55 56 57 58 this.advisorChainInitialized = true; 59
增加advisor chain(AdvisedSupport.java)
1 private void addAdvisorInternal(int pos, Advisor advisor) throws AopConfigException 2 Assert.notNull(advisor, "Advisor must not be null"); 3 if (isFrozen()) 4 throw new AopConfigException("Cannot add advisor: Configuration is frozen."); 5 6 if (pos > this.advisors.size()) 7 throw new IllegalArgumentException( 8 "Illegal position " + pos + " in advisor list with size " + this.advisors.size()); 9 10 this.advisors.add(pos, advisor); 11 updateAdvisorArray(); 12 adviceChanged(); 13
Spring AOP中拦截器链
1.开始步骤--获取AopProxy主流程
ProxyCreatorSupport.java
/** * Subclasses should call this to get a new AOP proxy. They should <b>not</b> * create an AOP proxy with <code>this</code> as an argument. */ protected final synchronized AopProxy createAopProxy() if (!this.active) activate(); return getAopProxyFactory().createAopProxy(this);
2.获取AopProxy实现 --DefaultAopProxyFactory.java
ProxyFactoryBean类继承了AdvisedSupport类,后者继承了ProxyConfig类并定义了操作advisor 和interceptor的接口,以支持AOP。当BeanFactory实例化ProxyFactoryBean时,根据配置文件的定义将关于 advice,pointcut,advisor,所代理的接口和接口实现类的所有信息传给ProxyFactoryBean。
当客户程序调用BeanFactory的getBean方法时,ProxyFactory使用JdkDynamicAopProxy实例化 BeanImpl类,并用JdkDynamicAopProxy的invoke方法执行advice。至于执行advice的时机,由 ProxyFactoryBean调用RegexpMethodPointcutAdvisor进行判断。
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); if (!cglibAvailable) throw new AopConfigException( "Cannot proxy target class because CGLIB2 is not available. " + "Add CGLIB to the class path or specify proxy interfaces."); return CglibProxyFactory.createCglibProxy(config); else return new JdkDynamicAopProxy(config);
3.获取AopProxy的执行路径
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);
4.激发拦截器链主过程
1 /** 2 * Implementation of <code>InvocationHandler.invoke</code>. 3 * <p>Callers will see exactly the exception thrown by the target, 4 * unless a hook method throws an exception. 5 */ 6 public Object invoke(Object proxy, Method method, Object[] args) throws Throwable 7 MethodInvocation invocation = null; 8 Object oldProxy = null; 9 boolean setProxyContext = false; 10 11 TargetSource targetSource = this.advised.targetSource; 12 Class targetClass = null; 13 Object target = null; 14 15 try 16 if (!this.equalsDefined && AopUtils.isEqualsMethod(method)) 17 // The target does not implement the equals(Object) method itself. 18 return (equals(args[0]) ? Boolean.TRUE : Boolean.FALSE); 19 20 if (!this.hashCodeDefined && AopUtils.isHashCodeMethod(method)) 21 // The target does not implement the hashCode() method itself. 22 return new Integer(hashCode()); 23 24 if (!this.advised.opaque && method.getDeclaringClass().isInterface() && 25 method.getDeclaringClass().isAssignableFrom(Advised.class)) 26 // Service invocations on ProxyConfig with the proxy config... 27 return AopUtils.invokeJoinpointUsingReflection(this.advised, method, args); 28 29 30 Object retVal = null; 31 32 if (this.advised.exposeProxy) 33 // Make invocation available if necessary. 34 oldProxy = AopContext.setCurrentProxy(proxy); 35 setProxyContext = true; 36 37 38 // May be <code>null</code>. Get as late as possible to minimize the time we "own" the target, 39 // in case it comes from a pool. 40 target = targetSource.getTarget(); 41 if (target != null) 42 targetClass = target.getClass(); 43 44 45 // Get the interception chain for this method. 46 List chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass); 47 48 // Check whether we have any advice. If we don‘t, we can fallback on direct 49 // reflective invocation of the target, and avoid creating a MethodInvocation. 50 if (chain.isEmpty()) 51 // We can skip creating a MethodInvocation: just invoke the target directly 52 // Note that the final invoker must be an InvokerInterceptor so we know it does 53 // nothing but a reflective operation on the target, and no hot swapping or fancy proxying. 54 retVal = AopUtils.invokeJoinpointUsingReflection(target, method, args); 55 56 else 57 // We need to create a method invocation... 58 invocation = new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain); 59 // Proceed to the joinpoint through the interceptor chain. 60 retVal = invocation.proceed(); 61 62 63 // Massage return value if necessary. 64 if (retVal != null && retVal == target && method.getReturnType().isInstance(proxy) && 65 !RawTargetAccess.class.isAssignableFrom(method.getDeclaringClass())) 66 // Special case: it returned "this" and the return type of the method 67 // is type-compatible. Note that we can‘t help if the target sets 68 // a reference to itself in another returned object. 69 retVal = proxy; 70 71 return retVal; 72 73 finally 74 if (target != null && !targetSource.isStatic()) 75 // Must have come from TargetSource. 76 targetSource.releaseTarget(target); 77 78 if (setProxyContext) 79 // Restore old proxy. 80 AopContext.setCurrentProxy(oldProxy); 81 82 83
5.获取拦截器链DefaultAdvisorChainFactory.java
public List 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 interceptorList = new ArrayList(config.getAdvisors().length); boolean hasIntroductions = hasMatchingIntroductions(config, targetClass); AdvisorAdapterRegistry registry = GlobalAdvisorAdapterRegistry.getInstance(); Advisor[] advisors = config.getAdvisors(); for (int i = 0; i < advisors.length; i++) Advisor advisor = advisors[i]; if (advisor instanceof PointcutAdvisor) // Add it conditionally. PointcutAdvisor pointcutAdvisor = (PointcutAdvisor) advisor; if (config.isPreFiltered() || pointcutAdvisor.getPointcut().getClassFilter().matches(targetClass)) MethodInterceptor[] interceptors = registry.getInterceptors(advisor); MethodMatcher mm = pointcutAdvisor.getPointcut().getMethodMatcher(); if (MethodMatchers.matches(mm, method, targetClass, hasIntroductions)) if (mm.isRuntime()) // Creating a new object instance in the getInterceptors() method // isn‘t a problem as we normally cache created chains. for (int j = 0; j < interceptors.length; j++) interceptorList.add(new InterceptorAndDynamicMethodMatcher(interceptors[j], mm)); else interceptorList.addAll(Arrays.asList(interceptors)); else if (advisor instanceof IntroductionAdvisor) IntroductionAdvisor ia = (IntroductionAdvisor) advisor; if (config.isPreFiltered() || ia.getClassFilter().matches(targetClass)) Interceptor[] interceptors = registry.getInterceptors(advisor); interceptorList.addAll(Arrays.asList(interceptors)); else Interceptor[] interceptors = registry.getInterceptors(advisor); interceptorList.addAll(Arrays.asList(interceptors)); return interceptorList; 6.激发拦截链工作实现 ---ReflectiveMethodInvocation.java 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; 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. 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);
Spring AOP中Aspect编织的实现
1.前面我们谈到拦截器起作用时,实现代码(ReflectiveMethodInvocation.java)如下:
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; 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. 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);
2.前置Advice MethodBeforeAdviceInterceptor.java
public Object invoke(MethodInvocation mi) throws Throwable this.advice.before(mi.getMethod(), mi.getArguments(), mi.getThis() ); return mi.proceed();
3.后置Advice AfterReturningAdviceInterceptor.java
public Object invoke(MethodInvocation mi) throws Throwable Object retVal = mi.proceed(); this.advice.afterReturning(retVal, mi.getMethod(), mi.getArguments(), mi.getThis()); return retVal;
总结
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