AOP聯盟標準
AOP聯盟將AOP體系分爲三層,從三層結構可以看出,AOP實現方式有很多種,包括反射、元數據處理、程序處理、攔截器處理等,通過本節學習,你就會看到Spring AOP的實現使用的是Java語言本身的特性,即Java Proxy代理類、攔截器技術實現。
AOP簡介
概念
切面(Aspect) :官方的抽象定義爲“一個關注點的模塊化,這個關注點可能會橫切多個對象”。
連接點(Joinpoint) :程序執行過程中的某一行爲。
通知(Advice) :“切面”對於某個“連接點”所產生的動作。
切入點(Pointcut) :匹配連接點的斷言,在AOP中通知和一個切入點表達式關聯。
目標對象(Target Object) :被一個或者多個切面所通知的對象。
AOP代理(AOP Proxy) 在Spring AOP中有兩種代理方式,JDK動態代理和CGLIB代理。
通知(Advice)類型
前置通知(Before advice) :在某連接點(JoinPoint)之前執行的通知,但這個通知不能阻止連接點前的執行。ApplicationContext中在<aop:aspect>裏面使用<aop:before>元素進行聲明。
後通知(After advice) :當某連接點退出的時候執行的通知(不論是正常返回還是異常退出)。ApplicationContext中在<aop:aspect>裏面使用<aop:after>元素進行聲明。
返回後通知(After return advice) :在某連接點正常完成後執行的通知,不包括拋出異常的情況。ApplicationContext中在<aop:aspect>裏面使用<after-returning>元素進行聲明。
環繞通知(Around advice) :包圍一個連接點的通知,類似Web中Servlet規範中的Filter的doFilter方法。可以在方法的調用前後完成自定義的行爲,也可以選擇不執行。ApplicationContext中在<aop:aspect>裏面使用<aop:around>元素進行聲明。
拋出異常後通知(After throwing advice) : 在方法拋出異常退出時執行的通知。 ApplicationContext中在<aop:aspect>裏面使用<aop:after-throwing>元素進行聲明。
切入點表達式 :如execution(* com.spring.service.*.*(..))
特點
1、降低模塊之間的耦合度
2、使系統容易擴展
3、更好的代碼複用。
時序圖
流程說明
1)AOP標籤的定義解析劉徹骨肯定是從NamespaceHandlerSupport的實現類開始解析的,這個實現類就是AopNamespaceHandler。至於爲什麼會是從NamespaceHandlerSupport的實現類開始解析的,這個的話我想讀者可以去在回去看看Spring自定義標籤的解析流程,裏面說的比較詳細。
2)要啓用AOP,我們一般會在Spring裏面配置<aop:aspectj-autoproxy/> ,所以在配置文件中在遇到aspectj-autoproxy標籤的時候我們會採用AspectJAutoProxyBeanDefinitionParser解析器
3)進入AspectJAutoProxyBeanDefinitionParser解析器後,調用AspectJAutoProxyBeanDefinitionParser已覆蓋BeanDefinitionParser的parser方法,然後parser方法把請求轉交給了AopNamespaceUtils的registerAspectJAnnotationAutoProxyCreatorIfNecessary去處理
4)進入AopNamespaceUtils的registerAspectJAnnotationAutoProxyCreatorIfNecessary方法後,先調用AopConfigUtils的registerAspectJAnnotationAutoProxyCreatorIfNecessary方法,裏面在轉發調用給registerOrEscalateApcAsRequired,註冊或者升級AnnotationAwareAspectJAutoProxyCreator類。對於AOP的實現,基本是靠AnnotationAwareAspectJAutoProxyCreator去完成的,它可以根據@point註解定義的切點來代理相匹配的bean。
5)AopConfigUtils的registerAspectJAnnotationAutoProxyCreatorIfNecessary方法處理完成之後,接下來會調用useClassProxyingIfNecessary() 處理proxy-target-class以及expose-proxy屬性。如果將proxy-target-class設置爲true的話,那麼會強制使用CGLIB代理,否則使用jdk動態代理,expose-proxy屬性是爲了解決有時候目標對象內部的自我調用無法實現切面增強。
6)最後的調用registerComponentIfNecessary 方法,註冊組建並且通知便於監聽器做進一步處理。
創建AOP代理
上面說到AOP的核心邏輯是在AnnotationAwareAspectJAutoProxyCreator類裏面實現,那麼我們先來看看這個類的層次關係
這個類實現了BeanPostProcessor接口,那就意味着這個類在spring加載實例化前會調用postProcessAfterInitialization方法,對於AOP的邏輯也是由此開始的。
時序圖
流程說明
1)spring 容器啓動,每個bean的實例化之前都會先經過AbstractAutoProxyCreator類的postProcessAfterInitialization()這個方法,然後接下來是調用wrapIfNecessary方法。
/**
* Create a proxy with the configured interceptors if the bean is
* identified as one to proxy by the subclass.
* @see #getAdvicesAndAdvisorsForBean
*/
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
if (bean != null) {
Object cacheKey = getCacheKey(bean.getClass(), beanName);
if (!this.earlyProxyReferences.containsKey(cacheKey)) {
return wrapIfNecessary(bean, beanName, cacheKey);
}
}
return bean;
}
2)進入wrapIfNecessary方法後,我們直接看重點實現邏輯的方法getAdvicesAndAdvisorsForBean,這個方法會提取當前bean 的所有增強方法,然後獲取到適合的當前bean 的增強方法,然後對增強方法進行排序,最後返回
/**
* Wrap the given bean if necessary, i.e. if it is eligible for being proxied.
* @param bean the raw bean instance
* @param beanName the name of the bean
* @param cacheKey the cache key for metadata access
* @return a proxy wrapping the bean, or the raw bean instance as-is
*/
protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
if (beanName != null && this.targetSourcedBeans.containsKey(beanName)) {
return bean;
}
if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) {
return bean;
}
if (isInfrastructureClass(bean.getClass()) || shouldSkip(bean.getClass(), beanName)) {
this.advisedBeans.put(cacheKey, Boolean.FALSE);
return bean;
}
// Create proxy if we have advice.
Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
if (specificInterceptors != DO_NOT_PROXY) {
this.advisedBeans.put(cacheKey, Boolean.TRUE);
Object proxy = createProxy(bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));
this.proxyTypes.put(cacheKey, proxy.getClass());
return proxy;
}
this.advisedBeans.put(cacheKey, Boolean.FALSE);
return bean;
}
3)獲取到當前bean的增強方法後,便調用createProxy方法,創建代理。先創建代理工廠proxyFactory,然後獲取當前bean 的增強器advisors,把當前獲取到的增強器添加到代理工廠proxyFactory,然後設置當前的代理工的代理目標對象爲當前bean,最後根據配置創建JDK的動態代理工廠,或者CGLIB的動態代理工廠,然後返回proxyFactory
/**
* Create an AOP proxy for the given bean.
* @param beanClass the class of the bean
* @param beanName the name of the bean
* @param specificInterceptors the set of interceptors that is
* specific to this bean (may be empty, but not null)
* @param targetSource the TargetSource for the proxy,
* already pre-configured to access the bean
* @return the AOP proxy for the bean
* @see #buildAdvisors
*/
protected Object createProxy(
Class<?> beanClass, String beanName, Object[] specificInterceptors, TargetSource targetSource) {
ProxyFactory proxyFactory = new ProxyFactory();
// Copy our properties (proxyTargetClass etc) inherited from ProxyConfig.
proxyFactory.copyFrom(this);
if (!shouldProxyTargetClass(beanClass, beanName)) {
// Must allow for introductions; can't just set interfaces to
// the target's interfaces only.
Class<?>[] targetInterfaces = ClassUtils.getAllInterfacesForClass(beanClass, this.proxyClassLoader);
for (Class<?> targetInterface : targetInterfaces) {
proxyFactory.addInterface(targetInterface);
}
}
Advisor[] advisors = buildAdvisors(beanName, specificInterceptors);
for (Advisor advisor : advisors) {
proxyFactory.addAdvisor(advisor);
}
proxyFactory.<strong>setTargetSource</strong>(targetSource);
customizeProxyFactory(proxyFactory);
proxyFactory.setFrozen(this.freezeProxy);
if (advisorsPreFiltered()) {
proxyFactory.setPreFiltered(true);
}
return proxyFactory.getProxy(this.proxyClassLoader);
}
AOP動態代理執行
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 CglibProxyFactory.createCglibProxy(config);
}
else {
return new JdkDynamicAopProxy(config);
}
}
Spring JDK動態代理實現
public Object invoke(Object proxy, Method method, Object[] args) throwsThrowable {
MethodInvocation invocation = null;
Object oldProxy = null;
boolean setProxyContext = false;
TargetSource targetSource = this.advised.targetSource;
Class targetClass = null;
Object target = null;
try {
//eqauls()方法,具目標對象未實現此方法
if (!this.equalsDefined && AopUtils.isEqualsMethod(method)){
return (equals(args[0])? Boolean.TRUE : Boolean.FALSE);
}
//hashCode()方法,具目標對象未實現此方法
if (!this.hashCodeDefined && AopUtils.isHashCodeMethod(method)){
return newInteger(hashCode());
}
//Advised接口或者其父接口中定義的方法,直接反射調用,不應用通知
if (!this.advised.opaque &&method.getDeclaringClass().isInterface()
&&method.getDeclaringClass().isAssignableFrom(Advised.class)) {
// Service invocations onProxyConfig with the proxy config...
return AopUtils.invokeJoinpointUsingReflection(this.advised,method, args);
}
Object retVal = null;
if (this.advised.exposeProxy) {
// Make invocation available ifnecessary.
oldProxy = AopContext.setCurrentProxy(proxy);
setProxyContext = true;
}
//獲得目標對象的類
target = targetSource.getTarget();
if (target != null) {
targetClass = target.getClass();
}
//獲取可以應用到此方法上的Interceptor列表
List chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method,targetClass);
//如果沒有可以應用到此方法的通知(Interceptor),此直接反射調用 method.invoke(target, args)
if (chain.isEmpty()) {
retVal = AopUtils.invokeJoinpointUsingReflection(target,method, args);
} else {
//創建MethodInvocation
invocation = newReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain);
retVal = invocation.proceed();
}
// Massage return value if necessary.
if (retVal != null && retVal == target &&method.getReturnType().isInstance(proxy)
&&!RawTargetAccess.class.isAssignableFrom(method.getDeclaringClass())) {
// Special case: it returned"this" and the return type of the method
// is type-compatible. Notethat we can't help if the target sets
// a reference to itself inanother returned object.
retVal = proxy;
}
return retVal;
} finally {
if (target != null && !targetSource.isStatic()) {
// Must have come fromTargetSource.
targetSource.releaseTarget(target);
}
if (setProxyContext) {
// Restore old proxy.
AopContext.setCurrentProxy(oldProxy);
}
}
}
public List<Object> getInterceptorsAndDynamicInterceptionAdvice(Method method, Class targetClass) {
MethodCacheKeycacheKey = 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);
}
returncached;
}
4)其實實際的獲取工作其實是由AdvisorChainFactory. getInterceptorsAndDynamicInterceptionAdvice()這個方法來完成的,獲取到的結果會被緩存,下面來分析下這個方法的實現:
/**
* 從提供的配置實例config中獲取advisor列表,遍歷處理這些advisor.如果是IntroductionAdvisor,
* 則判斷此Advisor能否應用到目標類targetClass上.如果是PointcutAdvisor,則判斷
* 此Advisor能否應用到目標方法method上.將滿足條件的Advisor通過AdvisorAdaptor轉化成Interceptor列表返回.
*/
publicList getInterceptorsAndDynamicInterceptionAdvice(Advised config, Methodmethod, 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);
//查看是否包含IntroductionAdvisor
boolean hasIntroductions = hasMatchingIntroductions(config,targetClass);
//這裏實際上註冊一系列AdvisorAdapter,用於將Advisor轉化成MethodInterceptor
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)) {
//TODO: 這個地方這兩個方法的位置可以互換下
//將Advisor轉化成Interceptor
MethodInterceptor[]interceptors = registry.getInterceptors(advisor);
//檢查當前advisor的pointcut是否可以匹配當前方法
MethodMatcher mm =pointcutAdvisor.getPointcut().getMethodMatcher();
if (MethodMatchers.matches(mm,method, targetClass, hasIntroductions)) {
if(mm.isRuntime()) {
// Creating a newobject instance in the getInterceptors() method
// isn't a problemas we normally cache created chains.
for (intj = 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;
}
5)這個方法執行完成後,Advised中配置能夠應用到連接點或者目標類的Advisor全部被轉化成了MethodInterceptor.6)接下來貨到invoke方法中的proceed方法 ,我們再看下得到的攔截器鏈是怎麼起作用的,也就是proceed方法的執行過程
public Object proceed() throws Throwable {
// We start with an index of -1and increment early.
if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size()- 1) {
//如果Interceptor執行完了,則執行joinPoint
return invokeJoinpoint();
}
Object interceptorOrInterceptionAdvice =
this.interceptorsAndDynamicMethodMatchers.get(++this.currentInterceptorIndex);
//如果要動態匹配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;
//動態匹配:運行時參數是否滿足匹配條件
if (dm.methodMatcher.matches(this.method, this.targetClass,this.arguments)) {
//執行當前Intercetpor
returndm.interceptor.invoke(this);
}
else {
//動態匹配失敗時,略過當前Intercetpor,調用下一個Interceptor
return proceed();
}
}
else {
// It's an interceptor, so we just invoke it: The pointcutwill have
// been evaluated statically before this object was constructed.
//執行當前Intercetpor
return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);
}
}