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AOP 源码解析之二 - 创立 AOP 代理前传，获取 AOP 信息。
上篇文章对 AOP 的基本概念说分明了，那么接下来的 AOP 还剩下两个大的步骤获取定义的 AOP 信息，生成代理对象扔到 beanFactory 中。
本篇文章重点对前半部分，如何获取到 AOP 信息的过程解读。
在 Spring 的外围办法 Refresh 办法中，aop 是在
Object bean = resolveBeforeInstantiation(beanName, mbdToUse);开始切入的，该文章就开始深刻这个办法进行解析。
@Nullable
protected Object resolveBeforeInstantiation(String beanName, RootBeanDefinition mbd) {
Object bean = null;
// 检测是否被解析过
if (!Boolean.FALSE.equals(mbd.beforeInstantiationResolved)) {
// Make sure bean class is actually resolved at this point.
// hasInstantiationAwareBeanPostProcessors() 是来判断容器中是否有 InstantiationAwareBeanPostProcessor 的实现 bean
// AOP 切面后置处理器 AspectJAwareAdvisorAutoProxyCreator 就实现了 InstantiationAwareBeanPostProcessor 接口
if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {Class<?> targetType = determineTargetType(beanName, mbd);
if (targetType != null) {
// 执行实现了 InstantiationAwareBeanPostProcessor 接口的 BeanPostProcessor 中的前置解决办法 postProcessBeforeInstantiation 办法
bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName);
if (bean != null) {
// 执行实现了 InstantiationAwareBeanPostProcessor 接口的 BeanPostProcessor 中的后置解决办法 postProcessAfterInitialization 办法
bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
}
}
}
mbd.beforeInstantiationResolved = (bean != null);
}
return bean;
}见名知意，resolveBeforeInstantiation（执行初始化前办法），这一步次要判断一下工厂中是否有 InstantiationAwareBeanPostProcessor 的实现 bean。InstantiationAwareBeanPostProcessor 应该是 AOP 最外围的接口了。
咱们看一下 InstantiationAwareBeanPostProcessor 的继承构造。
咱们具体的说下 InstantiationAwareBeanPostProcessor 这个接口。
public interface InstantiationAwareBeanPostProcessor extends BeanPostProcessor {Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException;
boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException;
PropertyValues postProcessPropertyValues(PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) throws BeansException;
}它和 BeanPostProcessor 的办法十分类似，而且它还继承了 BeanPostProcessor。
上面是 BeanPostProcessor 中的两个办法：
Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException;
Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException; 发现没有，InstantiationAwareBeanPostProcessor 是 Instantiation，BeanPostProcessor 是 Initialization，它代表的是 bean 在实例化实现并且属性注入实现，在执行 init-method 的前后进行作用的。
而 InstantiationAwareBeanPostProcessor 的执行机会要后面一些，咱们回到 refresh 办法的 doCreateBean 中看一下。
看到这读者想必对于 aop 的执行机会曾经隐隐约约的心里有个大略了。
咱们定义的盘绕告诉，创立代理肯定是在 postProcessBeforeInitialization 实现的。
咱们的重点就是看看 postProcessBeforeInitialization 的办法中的告诉怎么获取，怎么创立代理对象的进行具体的解读。
本文先对前半部分解读。
咱们持续看 postProcessBeforeInitialization 有哪些实现类。
咱们重点看 AbstractAutoProxyCreator 的实现类。
@Override
public Object postProcessAfterInitialization(@Nullable Object bean, String beanName) {if (bean != null) {Object cacheKey = getCacheKey(bean.getClass(), beanName);
// 1. 判断以后 bean 是否须要被代理，如果须要则进行封装
if (this.earlyProxyReferences.remove(cacheKey) != bean) {
//1. 判断以后 bean 是否须要被代理，如果须要则进行封装
return wrapIfNecessary(bean, beanName, cacheKey);
}
}
return bean;
}如果须要代理执行继 wrapIfNecessary 办法。
// 这个办法将返回代理类
protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
// 1. 判断以后 bean 是否在 targetSourcedBeans 缓存中存在（曾经解决过），如果存在，则间接返回以后 bean
if (StringUtils.hasLength(beanName) && this.targetSourcedBeans.contains(beanName)) {return bean;}
// 2. 在 advisedBeans 缓存中存在，并且 value 为 false，则代表无需解决
if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) {return bean;}
// 3.bean 的类是 aop 基础设施类 || bean 应该跳过，则标记为无需解决，并返回
if (isInfrastructureClass(bean.getClass()) || shouldSkip(bean.getClass(), beanName)) {this.advisedBeans.put(cacheKey, Boolean.FALSE);
return bean;
}
// Create proxy if we have advice.
// 4. 获取以后 bean 的 Advices 和 Advisors
Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
// 5. 如果存在增强器则创立代理
if (specificInterceptors != DO_NOT_PROXY) {this.advisedBeans.put(cacheKey, Boolean.TRUE);
// 创立代理... 创立代理... 创立代理...
// 5.1 创立代理对象：这边 SingletonTargetSource 的 target 属性寄存的就是咱们原来的 bean 实例（也就是被代理对象），// 用于最初减少逻辑执行结束后，通过反射执行咱们真正的办法时应用（method.invoke(bean, args)）Object proxy = createProxy(bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));
// 5.2 创立完代理后，将 cacheKey -> 代理类的 class 放到缓存
this.proxyTypes.put(cacheKey, proxy.getClass());
return proxy;
}
// 6. 标记为无需解决
this.advisedBeans.put(cacheKey, Boolean.FALSE);
return bean;
}4.1 咱们先查看第一条主线，获取以后 bean 的 Advices 和 Advisors
@Override
@Nullable
protected Object[] getAdvicesAndAdvisorsForBean(Class<?> beanClass, String beanName, @Nullable TargetSource targetSource) {
// 1. 找到符合条件的 Advisor
List<Advisor> advisors = findEligibleAdvisors(beanClass, beanName);
if (advisors.isEmpty()) {
// 2. 如果没有符合条件的 Advisor，则返回 null
return DO_NOT_PROXY;
}
return advisors.toArray();}注：Advisors 即是 aop 的盘绕告诉。
protected List<Advisor> findEligibleAdvisors(Class<?> beanClass, String beanName) {
// 1. 查找所有的候选 Advisor
List<Advisor> candidateAdvisors = findCandidateAdvisors();
// 2. 从所有候选的 Advisor 中找出符合条件的
List<Advisor> eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);
// 3. 扩大办法，留个子类实现
extendAdvisors(eligibleAdvisors);
if (!eligibleAdvisors.isEmpty()) {
// 4. 对符合条件的 Advisor 进行排序
eligibleAdvisors = sortAdvisors(eligibleAdvisors);
}
return eligibleAdvisors;
}这一步所做的事很简略，就是查找所有候选的 Advisor，然而调用链路特地的长，如果将这些彻底搞明确，还是须要消耗一番功夫的，读者能够抉择深刻水平。
1、寻找可用的 Advisor
public List<Advisor> findAdvisorBeans() {
// Determine list of advisor bean names, if not cached already.
// 1. 确认 advisor 的 beanName 列表，优先从缓存中拿
String[] advisorNames = this.cachedAdvisorBeanNames;
if (advisorNames == null) {
// Do not initialize FactoryBeans here: We need to leave all regular beans
// uninitialized to let the auto-proxy creator apply to them!
// 1.1 如果缓存为空，则获取 class 类型为 Advisor 的所有 bean 名称
advisorNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(this.beanFactory, Advisor.class, true, false);
this.cachedAdvisorBeanNames = advisorNames;
}
if (advisorNames.length == 0) {return new ArrayList<>();
}
// 2. 遍历解决 advisorNames
List<Advisor> advisors = new ArrayList<>();
for (String name : advisorNames) {if (isEligibleBean(name)) {
// 2.1 跳过以后正在创立的 advisor
if (this.beanFactory.isCurrentlyInCreation(name)) {if (logger.isTraceEnabled()) {logger.trace("Skipping currently created advisor'" + name + "'");
}
}
else {
try {
// 2.2 通过 beanName 获取对应的 bean 对象，并增加到 advisors
advisors.add(this.beanFactory.getBean(name, Advisor.class));
}
catch (BeanCreationException ex) {Throwable rootCause = ex.getMostSpecificCause();
if (rootCause instanceof BeanCurrentlyInCreationException) {BeanCreationException bce = (BeanCreationException) rootCause;
String bceBeanName = bce.getBeanName();
if (bceBeanName != null && this.beanFactory.isCurrentlyInCreation(bceBeanName)) {if (logger.isTraceEnabled()) {
logger.trace("Skipping advisor'" + name +
"'with dependency on currently created bean:" + ex.getMessage());
}
// Ignore: indicates a reference back to the bean we're trying to advise.
// We want to find advisors other than the currently created bean itself.
continue;
}
}
throw ex;
}
}
}
}
// 3. 返回符合条件的 advisor 列表
return advisors;
}/**
* 找到符合条件的 Advisor
* @return
*/
@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.
if (this.aspectJAdvisorsBuilder != null) {advisors.addAll(this.aspectJAdvisorsBuilder.buildAspectJAdvisors());
}
return advisors;
}public List<Advisor> buildAspectJAdvisors() {
List<String> aspectNames = this.aspectBeanNames;
// 1. 如果 aspectNames 为空，则进行解析
if (aspectNames == null) {synchronized (this) {
aspectNames = this.aspectBeanNames;
if (aspectNames == null) {List<Advisor> advisors = new ArrayList<>();
aspectNames = new ArrayList<>();
// 1.1 获取所有的 beanName
String[] beanNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(this.beanFactory, Object.class, true, false);
// 1.2 循环遍历所有的 beanName，找出对应的加强办法
for (String beanName : beanNames) {
// 1.3 不非法的 beanName 则跳过，默认返回 true，子类能够笼罩实现，AnnotationAwareAspectJAutoProxyCreator
// 实现了本人的逻辑，反对应用 includePatterns 进行筛选
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.
// 获取 beanName 对应的 bean 的类型
Class<?> beanType = this.beanFactory.getType(beanName);
if (beanType == null) {continue;}
// 1.4 如果 beanType 存在 Aspect 注解则进行解决
if (this.advisorFactory.isAspect(beanType)) {
// 将存在 Aspect 注解的 beanName 增加到 aspectNames 列表
aspectNames.add(beanName);
// 新建切面元数据
AspectMetadata amd = new AspectMetadata(beanType, beanName);
if (amd.getAjType().getPerClause().getKind() == PerClauseKind.SINGLETON) {
// 应用 BeanFactory 和 beanName 创立一个 BeanFactoryAspectInstanceFactory，次要用来创立切面对象实例
MetadataAwareAspectInstanceFactory factory =
new BeanFactoryAspectInstanceFactory(this.beanFactory, beanName);
// 1.5 解析标记 AspectJ 注解中的加强办法 *********************
List<Advisor> classAdvisors = this.advisorFactory.getAdvisors(factory);
// 1.6 放到缓存中
if (this.beanFactory.isSingleton(beanName)) {
// 如果 beanName 是单例则间接将解析的加强办法放到缓存
this.advisorsCache.put(beanName, classAdvisors);
}
else {
// 如果不是单例，则将 factory 放到缓存，之后能够通过 factory 来解析加强办法
this.aspectFactoryCache.put(beanName, factory);
}
// 1.7 将解析的增强器增加到 advisors
advisors.addAll(classAdvisors);
}
else {
// Per target or per this.
if (this.beanFactory.isSingleton(beanName)) {
// 名称为 beanName 的 Bean 是单例，但切面实例化模型不是单例，则抛异样
throw new IllegalArgumentException("Bean with name'" + beanName +
"'is a singleton, but aspect instantiation model is not singleton");
}
MetadataAwareAspectInstanceFactory factory =
new PrototypeAspectInstanceFactory(this.beanFactory, beanName);
// 将 factory 放到缓存，之后能够通过 factory 来解析加强办法
this.aspectFactoryCache.put(beanName, factory);
// 解析标记 AspectJ 注解中的加强办法，并增加到 advisors 中
advisors.addAll(this.advisorFactory.getAdvisors(factory));
}
}
}
// 1.9 将解析进去的切面 beanName 放到缓存 aspectBeanNames
this.aspectBeanNames = aspectNames;
return advisors;
}
}
}
if (aspectNames.isEmpty()) {return Collections.emptyList();
}
List<Advisor> advisors = new ArrayList<>();
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));
}
}
// 1.10 最初返回解析进去的增强器
return advisors;
}@Override
public List<Advisor> getAdvisors(MetadataAwareAspectInstanceFactory aspectInstanceFactory) {
// 1. 后面咱们将 beanClass 和 beanName 封装成了 aspectInstanceFactory 的 AspectMetadata 属性，// 这边能够通过 AspectMetadata 属性从新获取到以后解决的切面类
Class<?> aspectClass = aspectInstanceFactory.getAspectMetadata().getAspectClass();
// 2. 获取以后解决的切面类的名字
String aspectName = aspectInstanceFactory.getAspectMetadata().getAspectName();
// 3. 校验切面类
validate(aspectClass);
// We need to wrap the MetadataAwareAspectInstanceFactory with a decorator
// so that it will only instantiate once.
// 4. 应用装璜器包装 MetadataAwareAspectInstanceFactory，以便它只实例化一次。MetadataAwareAspectInstanceFactory lazySingletonAspectInstanceFactory =
new LazySingletonAspectInstanceFactoryDecorator(aspectInstanceFactory);
List<Advisor> advisors = new ArrayList<>();
// 5. 获取切面类中的办法（也就是咱们用来进行逻辑加强的办法，被 @Around、@After 等注解润饰的办法，应用 @Pointcut 的办法不解决）for (Method method : getAdvisorMethods(aspectClass)) {
// 6. 解决 method，获取增强器
Advisor advisor = getAdvisor(method, lazySingletonAspectInstanceFactory, advisors.size(), aspectName);
if (advisor != null) {
// 7. 如果增强器不为空，则增加到 advisors
advisors.add(advisor);
}
}
// If it's a per target aspect, emit the dummy instantiating aspect.
if (!advisors.isEmpty() && lazySingletonAspectInstanceFactory.getAspectMetadata().isLazilyInstantiated()) {
// 8. 如果寻找的增强器不为空而且又配置了加强提早初始化，那么须要在首位退出同步实例化增强器（用以保障加强应用之前的实例化）Advisor instantiationAdvisor = new SyntheticInstantiationAdvisor(lazySingletonAspectInstanceFactory);
advisors.add(0, instantiationAdvisor);
}
// Find introduction fields.
// 9. 获取 DeclareParents 注解
for (Field field : aspectClass.getDeclaredFields()) {Advisor advisor = getDeclareParentsAdvisor(field);
if (advisor != null) {advisors.add(advisor);
}
}
return advisors;
}@Override
@Nullable
public Advisor getAdvisor(Method candidateAdviceMethod, MetadataAwareAspectInstanceFactory aspectInstanceFactory,
int declarationOrderInAspect, String aspectName) {
// 1. 校验切面类
validate(aspectInstanceFactory.getAspectMetadata().getAspectClass());
// 2.AspectJ 切点信息的获取（例如：表达式），就是指定注解的表达式信息的获取，// 如：@Around("execution(* com.joonwhee.open.aop.*.*(..))")
AspectJExpressionPointcut expressionPointcut = getPointcut(candidateAdviceMethod, aspectInstanceFactory.getAspectMetadata().getAspectClass());
// 3. 如果 expressionPointcut 为 null，则间接返回 null
if (expressionPointcut == null) {return null;}
// 4. 依据切点信息生成增强器
return new InstantiationModelAwarePointcutAdvisorImpl(expressionPointcut, candidateAdviceMethod,
this, aspectInstanceFactory, declarationOrderInAspect, aspectName);
}获取到 @Before, @Around, @After, @AfterReturning, @AfterThrowing, @Pointcut 定义注解信息
@Nullable
private AspectJExpressionPointcut getPointcut(Method candidateAdviceMethod, Class<?> candidateAspectClass) {
// 1. 查找并返回给定办法的第一个 AspectJ 注解（@Before, @Around, @After, @AfterReturning, @AfterThrowing, @Pointcut）// 因为咱们之前把 @Pointcut 注解的办法跳过了，所以这边必然不会获取到 @Pointcut 注解
AspectJAnnotation<?> aspectJAnnotation =
AbstractAspectJAdvisorFactory.findAspectJAnnotationOnMethod(candidateAdviceMethod);
// 2. 如果办法没有应用 AspectJ 的注解，则返回 null
if (aspectJAnnotation == null) {return null;}
// 3. 应用 AspectJExpressionPointcut 实例封装获取的信息
AspectJExpressionPointcut ajexp =
new AspectJExpressionPointcut(candidateAspectClass, new String[0], new Class<?>[0]);
// 提取失去的注解中的表达式，// 例如：@Around("execution(* com.joonwhee.open.aop.*.*(..))")，失去：execution(* com.joonwhee.open.aop.*.*(..))
ajexp.setExpression(aspectJAnnotation.getPointcutExpression());
if (this.beanFactory != null) {ajexp.setBeanFactory(this.beanFactory);
}
return ajexp;
}@Nullable
protected static AspectJAnnotation<?> findAspectJAnnotationOnMethod(Method method) {
// 设置要查找的注解类
for (Class<?> clazz : ASPECTJ_ANNOTATION_CLASSES) {
// 查找办法上是否存在以后遍历的注解，如果有则返回
AspectJAnnotation<?> foundAnnotation = findAnnotation(method, (Class<Annotation>) clazz);
if (foundAnnotation != null) {return foundAnnotation;}
}
return null;
}2、获取切点当前就须要生成增强器了。
new InstantiationModelAwarePointcutAdvisorImpl(expressionPointcut, candidateAdviceMethod,
this, aspectInstanceFactory, declarationOrderInAspect, aspectName)/**
* 依据切点信息生成增强器
* @param declaredPointcut
* @param aspectJAdviceMethod
* @param aspectJAdvisorFactory
* @param aspectInstanceFactory
* @param declarationOrder
* @param aspectName
*/
public InstantiationModelAwarePointcutAdvisorImpl(AspectJExpressionPointcut declaredPointcut,
Method aspectJAdviceMethod, AspectJAdvisorFactory aspectJAdvisorFactory,
MetadataAwareAspectInstanceFactory aspectInstanceFactory, int declarationOrder, String aspectName) {
// 1. 简略的将信息封装在类的实例中
this.declaredPointcut = declaredPointcut;
this.declaringClass = aspectJAdviceMethod.getDeclaringClass();
this.methodName = aspectJAdviceMethod.getName();
this.parameterTypes = aspectJAdviceMethod.getParameterTypes();
// aspectJAdviceMethod 保留的是咱们用来进行逻辑加强的办法（@Around、@After 等润饰的办法）this.aspectJAdviceMethod = aspectJAdviceMethod;
this.aspectJAdvisorFactory = aspectJAdvisorFactory;
this.aspectInstanceFactory = aspectInstanceFactory;
this.declarationOrder = declarationOrder;
this.aspectName = aspectName;
// 2. 是否须要提早实例化
if (aspectInstanceFactory.getAspectMetadata().isLazilyInstantiated()) {
// Static part of the pointcut is a lazy type.
Pointcut preInstantiationPointcut = Pointcuts.union(aspectInstanceFactory.getAspectMetadata().getPerClausePointcut(), this.declaredPointcut);
// Make it dynamic: must mutate from pre-instantiation to post-instantiation state.
// If it's not a dynamic pointcut, it may be optimized out
// by the Spring AOP infrastructure after the first evaluation.
this.pointcut = new PerTargetInstantiationModelPointcut(this.declaredPointcut, preInstantiationPointcut, aspectInstanceFactory);
this.lazy = true;
}
else {
// A singleton aspect.
this.pointcut = this.declaredPointcut;
this.lazy = false;
// 3. 实例化增强器：依据注解中的信息初始化对应的增强器
this.instantiatedAdvice = instantiateAdvice(this.declaredPointcut);
}
}通过以上长长的源码剖析过程，就将 aop 的第一个大过程，获取到咱们定义的 @Before、@After 的办法当前，进行加强，下一步就要拿到这些获取的信息去创立代理对象了。
正文完
