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這篇文章主要介紹了spring中aop如何實現(xiàn),具有一定借鑒價值,感興趣的朋友可以參考下,希望大家閱讀完這篇文章之后大有收獲,下面讓小編帶著大家一起了解一下。
首先我們都知道aop的基本原理就是動態(tài)代理思想,在設(shè)計模式之代理模式中有介紹過這兩種動態(tài)代理的使用與基本原理,再次不再敘述。
這里分析的是,在spring中是如何基于動態(tài)代理的思想實現(xiàn)aop的。為了方便了解接下來的源碼分析,這里簡單化了一個流程圖分析aop的基本實現(xiàn)思想。
so,基于上面的流程,一步步分析spring源碼中的aop實現(xiàn)方式。
采用一個簡單的aop例子,利用基于注解配置方式的切面配置,分析一個簡單的Before AOP例子。在spring boot下運(yùn)行以下簡單例子。
AOP的advisor和advice配置。
@Component @Aspect public class AopConfig { @Pointcut("execution(* com.garine.debug.testcase.model.AopObject..*(..))") public void mypoint(){ //切面定義 } @Before("mypoint()") public void doAround() throws Throwable { System.out.println("before logic"); } }
AopObject,被代理攔截對象。
@Component public class AopObject { public void aoped(){ System.out.println("logic"); } }
首先是第一步內(nèi)容,對我們在AopConfig中的AOP配置內(nèi)容進(jìn)行解析并且保存到BeanFactory中,這個過程就是解析保存切面信息。
經(jīng)過一遍的代碼跟蹤,我了解到注解方式的AOP配置,都離不開一個類–AnnotationAwareAspectJAutoProxyCreator,這個類繼承了BeanPostProcessor接口,我們都知道BeanPostProcessor的實現(xiàn)類有多個執(zhí)行處理節(jié)點,其中一個執(zhí)行節(jié)點就是在Bean實例化之后。也就是在這個時機(jī)AnnotationAwareAspectJAutoProxyCreator攔截bean的初始化過程,根據(jù)提前解析得到的切面信息,對bean的方法進(jìn)行嘗試適配,如果有匹配則需要進(jìn)行代理創(chuàng)建。
這里先分析的就是AnnotationAwareAspectJAutoProxyCreator,在bean實例化第一次查詢所有切面信息時,就會解析保存Aop的信息到實例中,跟蹤以下代碼。
AbstractApplicationContext#refresh (上下文初始化主干方法)
AbstractApplicationContext#registerBeanPostProcessors (執(zhí)行實例化并保存所有實現(xiàn)BeanPostProcessor接口的類)
按照上面的邏輯,registerBeanPostProcessors 會比一般的bean實例化邏輯要早執(zhí)行,因此我們接下來只需要分析AnnotationAwareAspectJAutoProxyCreator的初始化過程。
通過上圖可以知道,AnnotationAwareAspectJAutoProxyCreator是繼承了BeanfactoryAware接口,所以在實例化時,會執(zhí)行setFactory方法。而所有切面信息解析的執(zhí)行者BeanFactoryAspectJAdvisorsBuilderAdapter初始化的時機(jī)也是在setFactory方法。
跟蹤代碼如下。
AbstractAdvisorAutoProxyCreator#setBeanFactory
AnnotationAwareAspectJAutoProxyCreator#initBeanFactory
在這個方法里面會新建一個BeanFactoryAspectJAdvisorsBuilderAdapter,這個對象會根據(jù)Beanfactory內(nèi)的aop配置信息,進(jìn)行解析保存。但是需要注意,此時雖然新建了BeanFactoryAspectJAdvisorsBuilderAdapter對象.但是此時還不會馬上解析aop配置,需要在第一次個普通bean實例化時才執(zhí)行解析aop配置。解析的方法就是
BeanFactoryAspectJAdvisorsBuilder#buildAspectJAdvisors,會在初次執(zhí)行AnnotationAwareAspectJAutoProxyCreator調(diào)用postProcessBeforeInitialization時開始執(zhí)行。
protected void initBeanFactory(ConfigurableListableBeanFactory beanFactory) { super.initBeanFactory(beanFactory); //aspectJAdvisorsBuilder#buildAspectJAdvisors就是解析配置入口 this.aspectJAdvisorsBuilder = new BeanFactoryAspectJAdvisorsBuilderAdapter(beanFactory, this.aspectJAdvisorFactory); }
上面提到繼承結(jié)構(gòu)圖中,AnnotationAwareAspectJAutoProxyCreator是實現(xiàn)了InstantiationAwareBeanPostProcessor接口的,InstantiationAwareBeanPostProcessor接口定義的postProcessBeforeInitialization方法是一個可以對已經(jīng)注入依賴屬性的bean對象實例進(jìn)行編輯操作的接口,會在
AbstractAutowireCapableBeanFactory#doCreateBean
AbstractAutowireCapableBeanFactory#initializeBean(String, Object, RootBeanDefinition)
AbstractAutowireCapableBeanFactory#applyBeanPostProcessorsBeforeInstantiation
方法中執(zhí)行InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation,初次初始化緩存切面信息的話就是在這個方法里面。。
具體的調(diào)用鏈如上所示。這里的postProcessBeforeInstantiation方法實際上是AnnotationAwareAspectJAutoProxyCreator的實例進(jìn)行調(diào)用,AnnotationAwareAspectJAutoProxyCreator實現(xiàn)InstantiationAwareBeanPostProcessor接口。
下面進(jìn)入InstantiationAwareBeanPostProcessor#postProcessBeforeInitialization方法分析代碼。
AbstractAutoProxyCreator#postProcessBeforeInstantiation
AspectJAwareAdvisorAutoProxyCreator#shouldSkip (關(guān)鍵代碼)
進(jìn)入如下代碼AbstractAutoProxyCreator,這個實例也就是之前一開始初始化的AnnotationAwareAspectJAutoProxyCreator實例,進(jìn)入實例的shouldSkip 方法
@Override protected boolean shouldSkip(Class<?> beanClass, String beanName) { // TODO: Consider optimization by caching the list of the aspect names //預(yù)先解析緩存切面信息 List<Advisor> candidateAdvisors = findCandidateAdvisors(); for (Advisor advisor : candidateAdvisors) { if (advisor instanceof AspectJPointcutAdvisor) { if (((AbstractAspectJAdvice) advisor.getAdvice()).getAspectName().equals(beanName)) { return true; } } } return super.shouldSkip(beanClass, beanName); }
AnnotationAwareAspectJAutoProxyCreator#findCandidateAdvisors
方法findCandidateAdvisors代碼如下,這里是預(yù)先解析緩存所有切面advisor信息,注意這一步操作是在AbstractAutoProxyCreator#postProcessBeforeInitialization處理,也就是開頭提到的切面解析操作,解析完成就進(jìn)行緩存。
@Override protected List<Advisor> findCandidateAdvisors() { // Add all the Spring advisors found according to superclass rules. List<Advisor> advisors = super.findCandidateAdvisors(); // Build Advisors for all AspectJ aspects in the bean factory. //這里就是前面提到的BeanFactoryAspectJAdvisorsBuilder解析所有切面信息的調(diào)用點 advisors.addAll(this.aspectJAdvisorsBuilder.buildAspectJAdvisors()); return advisors; }
然后繼續(xù)在這里先提前看一下是如何解析aop配置的。跟蹤BeanFactoryAspectJAdvisorsBuilder#buildAspectJAdvisors
public List<Advisor> buildAspectJAdvisors() { List<String> aspectNames = null; synchronized (this) { aspectNames = this.aspectBeanNames; if (aspectNames == null) { List<Advisor> advisors = new LinkedList<Advisor>(); aspectNames = new LinkedList<String>(); //查詢出Beanfactory中所有已經(jīng)注冊的BeanName String[] beanNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(this.beanFactory, Object.class, true, false); for (String beanName : beanNames) { if (!isEligibleBean(beanName)) { continue; } // We must be careful not to instantiate beans eagerly as in this // case they would be cached by the Spring container but would not // have been weaved Class<?> beanType = this.beanFactory.getType(beanName); if (beanType == null) { continue; } //判斷Bean是否是切面Bean,isAspect方法判斷[標(biāo)注1] if (this.advisorFactory.isAspect(beanType)) { aspectNames.add(beanName); AspectMetadata amd = new AspectMetadata(beanType, beanName); if (amd.getAjType().getPerClause().getKind() == PerClauseKind.SINGLETON) { MetadataAwareAspectInstanceFactory factory = new BeanFactoryAspectInstanceFactory(this.beanFactory, beanName); //解析aop class的配置,包返回Advisor對象[標(biāo)注2] List<Advisor> classAdvisors = this.advisorFactory.getAdvisors(factory); if (this.beanFactory.isSingleton(beanName)) { this.advisorsCache.put(beanName, classAdvisors); } else { this.aspectFactoryCache.put(beanName, factory); } advisors.addAll(classAdvisors); } else { // Per target or per this. if (this.beanFactory.isSingleton(beanName)) { throw new IllegalArgumentException("Bean with name '" + beanName + "' is a singleton, but aspect instantiation model is not singleton"); } MetadataAwareAspectInstanceFactory factory = new PrototypeAspectInstanceFactory(this.beanFactory, beanName); this.aspectFactoryCache.put(beanName, factory); advisors.addAll(this.advisorFactory.getAdvisors(factory)); } } } this.aspectBeanNames = aspectNames; return advisors; } } if (aspectNames.isEmpty()) { return Collections.emptyList(); } List<Advisor> advisors = new LinkedList<Advisor>(); for (String aspectName : aspectNames) { List<Advisor> cachedAdvisors = this.advisorsCache.get(aspectName); if (cachedAdvisors != null) { advisors.addAll(cachedAdvisors); } else { MetadataAwareAspectInstanceFactory factory = this.aspectFactoryCache.get(aspectName); advisors.addAll(this.advisorFactory.getAdvisors(factory)); } } return advisors; }
**[標(biāo)注1]如何判斷類是否是aop切面配置類? **
通過以下代碼。
@Override public boolean isAspect(Class<?> clazz) { return (hasAspectAnnotation(clazz) && !compiledByAjc(clazz)); } private boolean hasAspectAnnotation(Class<?> clazz) { //包含@Aspect注解 return (AnnotationUtils.findAnnotation(clazz, Aspect.class) != null); }
[標(biāo)注2]如何解析為Advisor對象?
ReflectiveAspectJAdvisorFactory#getAdvisors 遍歷所有沒被@PointCut注解標(biāo)注的方法,也就是遍歷切面內(nèi)容方法
ReflectiveAspectJAdvisorFactory#getAdvisor 處理所有沒被@PointCut注解標(biāo)注的方法,候選切面內(nèi)容方法
代碼如下。
@Override public Advisor getAdvisor(Method candidateAdviceMethod, MetadataAwareAspectInstanceFactory aspectInstanceFactory, int declarationOrderInAspect, String aspectName) { validate(aspectInstanceFactory.getAspectMetadata().getAspectClass()); //解析判斷候選方法是否有@Before,@After,@Around等注解,如果有,就繼續(xù)執(zhí)行新建Advisor對象。 AspectJExpressionPointcut expressionPointcut = getPointcut( candidateAdviceMethod, aspectInstanceFactory.getAspectMetadata().getAspectClass()); if (expressionPointcut == null) { return null; } //創(chuàng)建advisor return new InstantiationModelAwarePointcutAdvisorImpl(expressionPointcut, candidateAdviceMethod, this, aspectInstanceFactory, declarationOrderInAspect, aspectName); }
最終循環(huán)解析,@Before,@After,@Around等標(biāo)注的方法都會新建一個Advisor對象。新建的Advisor對象都保存在BeanFactoryAspectJAdvisorsBuilder#advisorsCache中,當(dāng)AnnotationAwareAspectJAutoProxyCreator攔截bean的創(chuàng)建過程時,從這里面適配是否有切面可用。
這里解析得到的Advisor,大概有以下信息。下面的信息中,并沒有對@PointCut注解做處理,pointCut屬性只得出一個"mypoint()",此時還不知道Advisor實際對應(yīng)的攔截表達(dá)式。
攔截表達(dá)式還是空的,會在AnnotationAwareAspectJAutoProxyCreator#postProcessAfterInstantiation第一次執(zhí)行時解析攔截表達(dá)式。
在AbstractAutoProxyCreator#postProcessAfterInitialization執(zhí)行時,找到上面AbstractAutoProxyCreator#postProcessBeforeInitialization緩存的所有的切面信息,之后是如何進(jìn)行切面適配,從而決定是否需要進(jìn)行代理對象的創(chuàng)建呢?
在調(diào)用AbstractAutoProxyCreator#postProcessAfterInitialization方法時,進(jìn)行切面適配,并且會根據(jù)適配創(chuàng)建代理對象。根據(jù)以下調(diào)用鏈。
AbstractAutoProxyCreator#postProcessAfterInitialization
AbstractAutoProxyCreator#wrapIfNecessary
protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) { if (beanName != null && this.targetSourcedBeans.contains(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. //查找匹配切面 Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null); if (specificInterceptors != DO_NOT_PROXY) { this.advisedBeans.put(cacheKey, Boolean.TRUE); //創(chuàng)建代理對象 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; }
AbstractAdvisorAutoProxyCreator#getAdvicesAndAdvisorsForBean
AbstractAdvisorAutoProxyCreator#findEligibleAdvisors
protected List<Advisor> findEligibleAdvisors(Class<?> beanClass, String beanName) { //從緩存取出所有切面信息 List<Advisor> candidateAdvisors = findCandidateAdvisors(); //根據(jù)advisor信息中的表達(dá)式進(jìn)行方法對class的匹配 List<Advisor> eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName); extendAdvisors(eligibleAdvisors); if (!eligibleAdvisors.isEmpty()) { eligibleAdvisors = sortAdvisors(eligibleAdvisors); } return eligibleAdvisors; }
此時如果是第一次執(zhí)行適配方法findAdvisorsThatCanApply的話,candidateAdvisors中的攔截表達(dá)式還是空的,需要進(jìn)行表達(dá)式獲取,也就是@Pointcut的value。spring的操作的在第一次執(zhí)行findAdvisorsThatCanApply時解析獲取攔截表達(dá)式的值,獲得攔截表達(dá)式值之后就跟當(dāng)前class的方法進(jìn)行匹配看是否需要進(jìn)行代理。
繼續(xù)往下跟蹤代碼
AopUtils#canApply(org.springframework.aop.Advisor, java.lang.Class<?>, boolean)
AopUtils#canApply(org.springframework.aop.Pointcut, java.lang.Class<?>, boolean)
AspectJExpressionPointcut#getClassFilter
AspectJExpressionPointcut#checkReadyToMatch
private void checkReadyToMatch() { if (getExpression() == null) { throw new IllegalStateException("Must set property 'expression' before attempting to match"); } if (this.pointcutExpression == null) { this.pointcutClassLoader = (this.beanFactory instanceof ConfigurableBeanFactory ? ((ConfigurableBeanFactory) this.beanFactory).getBeanClassLoader() : ClassUtils.getDefaultClassLoader()); //解析得到攔截表達(dá)式,例如根據(jù)@Before的value來關(guān)聯(lián)查詢出對應(yīng)的表達(dá)式 this.pointcutExpression = buildPointcutExpression(this.pointcutClassLoader); } }
最終解析完之后,advisor中的表達(dá)式信息結(jié)構(gòu)如下圖。包含在pointcut屬性中,匹配時就根據(jù)pointcutExpression循環(huán)進(jìn)行匹配class的方法。有興趣的可以繼續(xù)調(diào)試看看是如何實現(xiàn)匹配表達(dá)式的。
## 創(chuàng)建代理對象
如果在上面的匹配切面過程中,發(fā)現(xiàn)適配的切面,那就需要進(jìn)行代理對象的創(chuàng)建了。
我們回到上面的AbstractAutoProxyCreator#wrapIfNecessary,主要看代碼如下。
// Create proxy if we have advice. //查找匹配切面 Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null); if (specificInterceptors != DO_NOT_PROXY) { this.advisedBeans.put(cacheKey, Boolean.TRUE); //創(chuàng)建代理對象 Object proxy = createProxy( bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean)); this.proxyTypes.put(cacheKey, proxy.getClass()); return proxy; }
所以,繼續(xù)看
AbstractAutoProxyCreator#createProxy
的創(chuàng)建代理對象方法。設(shè)置ProxyFactory創(chuàng)建Proxy需要的一切信息。
protected Object createProxy( Class<?> beanClass, String beanName, Object[] specificInterceptors, TargetSource targetSource) { if (this.beanFactory instanceof ConfigurableListableBeanFactory) { AutoProxyUtils.exposeTargetClass((ConfigurableListableBeanFactory) this.beanFactory, beanName, beanClass); } //新建代理對象工廠 ProxyFactory proxyFactory = new ProxyFactory(); proxyFactory.copyFrom(this); //設(shè)置工廠代理類 if (!proxyFactory.isProxyTargetClass()) { if (shouldProxyTargetClass(beanClass, beanName)) { proxyFactory.setProxyTargetClass(true); } else { evaluateProxyInterfaces(beanClass, proxyFactory); } } //設(shè)置攔截切面 Advisor[] advisors = buildAdvisors(beanName, specificInterceptors); for (Advisor advisor : advisors) { proxyFactory.addAdvisor(advisor); } //設(shè)置被代理對象 proxyFactory.setTargetSource(targetSource); customizeProxyFactory(proxyFactory); proxyFactory.setFrozen(this.freezeProxy); if (advisorsPreFiltered()) { proxyFactory.setPreFiltered(true); } //創(chuàng)建代理對象 return proxyFactory.getProxy(getProxyClassLoader()); }
下面看ProxyFactory是如何創(chuàng)建代理對象,繼續(xù)跟蹤proxyFactory.getProxy(getProxyClassLoader());
public Object getProxy(ClassLoader classLoader) { return createAopProxy().getProxy(classLoader); }
createAopProxy()作用是根據(jù)class的種類判斷采用的代理方式,看如下實現(xiàn)
DefaultAopProxyFactory#createAopProxy
@Override 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() || Proxy.isProxyClass(targetClass)) { //采用jdk動態(tài)代理必須基于接口 return new JdkDynamicAopProxy(config); } //基于cglib實現(xiàn)代理不需要接口 return new ObjenesisCglibAopProxy(config); } else { return new JdkDynamicAopProxy(config); } }
所以在當(dāng)前調(diào)試的例子中,使用cglib代理。所以執(zhí)行如下代理。
@Override public Object getProxy(ClassLoader 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)); //獲取攔截回調(diào)函數(shù) 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. //返回一個cglib代理對象 return createProxyClassAndInstance(enhancer, callbacks); } catch (CodeGenerationException ex) { //、、、、、、 } }
getCallbacks(rootClass);在這個獲取回調(diào)函數(shù)的方法中,普通的aop采用的回調(diào)函數(shù)是如下的方式。
// Choose an "aop" interceptor (used for AOP calls). Callback aopInterceptor = new DynamicAdvisedInterceptor(this.advised);
cglib 的aop回調(diào)函數(shù)如下。
public Object intercept(Object proxy, Method method, Object[] args, MethodProxy methodProxy) throws Throwable { Object oldProxy = null; boolean setProxyContext = false; Class<?> targetClass = null; Object target = null; try { //這里注入的advised就是之前創(chuàng)建的ProxyFactory對象 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 = getTarget(); if (target != null) { targetClass = target.getClass(); } //根據(jù)切面信息創(chuàng)建切面內(nèi)容調(diào)用鏈 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... //創(chuàng)建一個方法調(diào)用對象,具體調(diào)用實現(xiàn)沒分析,Before邏輯大概是先調(diào)用切面,在反射調(diào)用目標(biāo)方法 retVal = new CglibMethodInvocation(proxy, target, method, args, targetClass, chain, methodProxy).proceed(); } retVal = processReturnType(proxy, target, method, retVal); return retVal; } finally { if (target != null) { releaseTarget(target); } if (setProxyContext) { // Restore old proxy. AopContext.setCurrentProxy(oldProxy); } } }
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