Spring AOP源码学习：创建 AOP 代理
强烈推介IDEA2020.2破解激活，IntelliJ IDEA 注册码，2020.2 IDEA 激活码
微信搜索【程序员囧辉】，关注这个坚持分享技术干货的程序员。
目录
前言
AnnotationAwareAspectJAutoProxyCreator
AbstractAutoProxyCreator#postProcessAfterInitialization
代码块1：wrapIfNecessary
代码块2：getAdvicesAndAdvisorsForBean
代码块3：findEligibleAdvisors
代码块4：findAdvisorBeans
代码块5：findCandidateAdvisors
代码块6：buildAspectJAdvisors
代码块7：getAdvisors
代码块8：getAdvisor
代码块9：getPointcut
代码块10：findAspectJAnnotationOnMethod
代码块11：new InstantiationModelAwarePointcutAdvisorImpl
代码块12：instantiateAdvice
代码块13：findAdvisorsThatCanApply
代码块14：createProxy
代码块15：getProxy
代码块16：createAopProxy
代码块17：JDK 动态代理、CBLIB 代理构造函数
代码块18：JdkDynamicAopProxy#getProxy
代码块19：CglibAopProxy#getProxy
代码块20：getCallbacks
总结
相关文章
前言
在上篇文章中 Spring AOP：AOP 注解的解析，我们解析了 AOP 注解，并注册了一个重要的 bean：AnnotationAwareAspectJAutoProxyCreator，AspectJ 方式的 AOP 的重要内容都在这个类里面，本文将详细介绍这个类及其相关方法。
之前提到的另外两种内部管理的自动代理创建者的 bean：InfrastructureAdvisorAutoProxyCreator、AspectJAwareAdvisorAutoProxyCreator 的实现基本和 AnnotationAwareAspectJAutoProxyCreator 一样。
AnnotationAwareAspectJAutoProxyCreator
AnnotationAwareAspectJAutoProxyCreator 实现了几个重要的扩展接口（可能是在父类中实现）：
1）实现了 BeanPostProcessor 接口：实现了 postProcessAfterInitialization 方法。
2）实现了 InstantiationAwareBeanPostProcessor 接口：实现了 postProcessBeforeInstantiation 方法。
3）实现了 SmartInstantiationAwareBeanPostProcessor 接口：实现了 predictBeanType 方法、getEarlyBeanReference 方法。
4）实现了 BeanFactoryAware 接口，实现了 setBeanFactory 方法。
对于 AOP 来说，postProcessAfterInitialization 是我们重点分析的内容，因为在该方法中，会对 bean 进行代理，该方法由父类 AbstractAutoProxyCreator 实现。
关于 postProcessAfterInitialization 方法，之前在介绍 BeanPostProcessor 接口时已经介绍过，可以简单的理解为所有 Spring 管理的 bean 在初始化后都会去调用所有 BeanPostProcessor 的 postProcessAfterInitialization 方法，详细的可以参考：Spring IoC：registerBeanPostProcessors 详解
AbstractAutoProxyCreator#postProcessAfterInitialization
代码语言：javascript复制@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
if (bean != null) {
Object cacheKey = getCacheKey(bean.getClass(), beanName);
// 1.判断当前bean是否需要被代理，如果需要则进行封装
if (!this.earlyProxyReferences.contains(cacheKey)) {
return wrapIfNecessary(bean, beanName, cacheKey);
}
}
return bean;
}1.判断当前bean是否需要被代理，如果需要则进行封装，见代码块1。
代码块1：wrapIfNecessary
代码语言：javascript复制protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
// 1.判断当前bean是否在targetSourcedBeans缓存中存在（已经处理过），如果存在，则直接返回当前bean
if (beanName != null && this.targetSourcedBeans.contains(beanName)) {
return bean;
}
// 2.在advisedBeans缓存中存在，并且value为false，则代表无需处理
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，则标记为无需处理，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.获取当前bean的Advices和Advisors
Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
// 5.如果存在增强器则创建代理
if (specificInterceptors != DO_NOT_PROXY) {
this.advisedBeans.put(cacheKey, Boolean.TRUE);
// 5.1 创建代理对象：这边SingletonTargetSource的target属性存放的就是我们原来的bean实例（也就是被代理对象），
// 用于最后增加逻辑执行完毕后，通过反射执行我们真正的方法时使用（method.invoke(bean, args)）
Object proxy = createProxy(
bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));
// 5.2 创建完代理后，将cacheKey -> 代理类的class放到缓存
this.proxyTypes.put(cacheKey, proxy.getClass());
// 返回代理对象
return proxy;
}
// 6.标记为无需处理
this.advisedBeans.put(cacheKey, Boolean.FALSE);
return bean;
}4.获取当前 bean 的 Advices 和 Advisors，见代码块2。
5.1 创建代理对象，见代码块14。
代码块2：getAdvicesAndAdvisorsForBean
代码语言：javascript复制@Override
protected Object[] getAdvicesAndAdvisorsForBean(Class<?> beanClass, String beanName, 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();
}1.找到符合条件的 Advisor，见代码块3。
代码块3：findEligibleAdvisors
代码语言：javascript复制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.扩展方法，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;
}1.查找所有的候选 Advisor，见代码块4。
2.从所有候选的 Advisor 中找出符合条件的，见代码块13。
代码块4：findAdvisorBeans
代码语言：javascript复制@Override
protected List<Advisor> findCandidateAdvisors() {
// 1.添加根据父类规则找到的所有advisor。
List<Advisor> advisors = super.findCandidateAdvisors();
// 2.为bean工厂中的所有AspectJ方面构建advisor
advisors.addAll(this.aspectJAdvisorsBuilder.buildAspectJAdvisors());
return advisors;
}1.添加根据父类规则找到的所有 advisor，见代码块5。
2.为 bean 工厂中的所有 AspectJ 方面构建 advisor，见代码块6。
代码块5：findCandidateAdvisors
代码语言：javascript复制protected List<Advisor> findCandidateAdvisors() {
return this.advisorRetrievalHelper.findAdvisorBeans();
}
public List<Advisor> findAdvisorBeans() {
// 1.确认advisor的beanName列表，优先从缓存中拿
String[] advisorNames = null;
synchronized (this) {
advisorNames = this.cachedAdvisorBeanNames;
if (advisorNames == null) {
// 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 LinkedList<Advisor>();
}
// 2.遍历处理advisorNames
List<Advisor> advisors = new LinkedList<Advisor>();
for (String name : advisorNames) {
if (isEligibleBean(name)) {
// 2.1 跳过当前正在创建的advisor
if (this.beanFactory.isCurrentlyInCreation(name)) {
if (logger.isDebugEnabled()) {
logger.debug("Skipping currently created advisor '" name "'");
}
} else {
try {
// 2.2 通过beanName获取对应的bean对象，并添加到advisors
advisors.add(this.beanFactory.getBean(name, Advisor.class));
} catch (BeanCreationException ex) {
Throwable rootCause = ex.getMostSpecificCause();
if (rootCause instanceof BeanCurrentlyInCreationException) {
BeanCreationException bce = (BeanCreationException) rootCause;
if (this.beanFactory.isCurrentlyInCreation(bce.getBeanName())) {
if (logger.isDebugEnabled()) {
logger.debug("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;
}代码块6：buildAspectJAdvisors
代码语言：javascript复制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 LinkedList<Advisor>();
aspectNames = new LinkedList<String>();
// 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，找出对应的增强方法
for (String beanName : beanNames) {
// 1.3 不合法的beanName则跳过，默认返回true，子类可以覆盖实现，AnnotationAwareAspectJAutoProxyCreator
// 实现了自己的逻辑，支持使用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注解则进行处理
if (this.advisorFactory.isAspect(beanType)) {
// 将存在Aspect注解的beanName添加到aspectNames列表
aspectNames.add(beanName);
// 新建切面元数据
AspectMetadata amd = new AspectMetadata(beanType, beanName);
// 获取per-clause的类型是SINGLETON
if (amd.getAjType().getPerClause().getKind() == PerClauseKind.SINGLETON) {
// 使用BeanFactory和beanName创建一个BeanFactoryAspectInstanceFactory，主要用来创建切面对象实例
MetadataAwareAspectInstanceFactory factory =
new BeanFactoryAspectInstanceFactory(this.beanFactory, beanName);
// 1.5 解析标记AspectJ注解中的增强方法
List<Advisor> classAdvisors = this.advisorFactory.getAdvisors(factory);
// 1.6 放到缓存中
if (this.beanFactory.isSingleton(beanName)) {
// 如果beanName是单例则直接将解析的增强方法放到缓存
this.advisorsCache.put(beanName, classAdvisors);
} else {
// 如果不是单例，则将factory放到缓存，之后可以通过factory来解析增强方法
this.aspectFactoryCache.put(beanName, factory);
}
// 1.7 将解析的增强器添加到advisors
advisors.addAll(classAdvisors);
} else {
// 如果per-clause的类型不是SINGLETON
// 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，则抛异常
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，之后可以通过factory来解析增强方法
this.aspectFactoryCache.put(beanName, factory);
// 解析标记AspectJ注解中的增强方法，并添加到advisors中
advisors.addAll(this.advisorFactory.getAdvisors(factory));
}
}
}
// 1.9 将解析出来的切面beanName放到缓存aspectBeanNames
this.aspectBeanNames = aspectNames;
// 1.10 最后返回解析出来的增强器
return advisors;
}
}
}
// 2.如果aspectNames不为null，则代表已经解析过了，则无需再次解析
// 2.1 如果aspectNames是空列表，则返回一个空列表。空列表也是解析过的，只要不是null都是解析过的。
if (aspectNames.isEmpty()) {
return Collections.emptyList();
}
// 2.2 aspectNames不是空列表，则遍历处理
List<Advisor> advisors = new LinkedList<Advisor>();
for (String aspectName : aspectNames) {
// 根据aspectName从缓存中获取增强器
List<Advisor> cachedAdvisors = this.advisorsCache.get(aspectName);
if (cachedAdvisors != null) {
// 根据上面的解析，可以知道advisorsCache存的是已经解析好的增强器，直接添加到结果即可
advisors.addAll(cachedAdvisors);
} else {
// 如果不存在于advisorsCache缓存，则代表存在于aspectFactoryCache中，
// 从aspectFactoryCache中拿到缓存的factory，然后解析出增强器，添加到结果中
MetadataAwareAspectInstanceFactory factory = this.aspectFactoryCache.get(aspectName);
advisors.addAll(this.advisorFactory.getAdvisors(factory));
}
}
// 返回增强器
return advisors;
}1.5 解析标记 AspectJ 注解中的增强方法，见代码块7。
代码块7：getAdvisors
代码语言：javascript复制@Override
public List<Advisor> getAdvisors(MetadataAwareAspectInstanceFactory aspectInstanceFactory) {
// 1.前面我们将beanClass和beanName封装成了aspectInstanceFactory的AspectMetadata属性，
// 这边可以通过AspectMetadata属性重新获取到当前处理的切面类
Class<?> aspectClass = aspectInstanceFactory.getAspectMetadata().getAspectClass();
// 2.获取当前处理的切面类的名字
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.使用装饰器包装MetadataAwareAspectInstanceFactory，以便它只实例化一次。
MetadataAwareAspectInstanceFactory lazySingletonAspectInstanceFactory =
new LazySingletonAspectInstanceFactoryDecorator(aspectInstanceFactory);
List<Advisor> advisors = new LinkedList<Advisor>();
// 5.获取切面类中的方法（也就是我们用来进行逻辑增强的方法，被@Around、@After等注解修饰的方法，使用@Pointcut的方法不处理）
for (Method method : getAdvisorMethods(aspectClass)) {
// 6.处理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，则添加到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增强延迟初始化，那么需要在首位加入同步实例化增强器（用以保证增强使用之前的实例化）
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;
}6.处理 method，获取增强器，见代码块8。
代码块8：getAdvisor
代码语言：javascript复制@Override
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，则直接返回null
if (expressionPointcut == null) {
return null;
}
// 4.根据切点信息生成增强器
return new InstantiationModelAwarePointcutAdvisorImpl(expressionPointcut, candidateAdviceMethod,
this, aspectInstanceFactory, declarationOrderInAspect, aspectName);
}2.AspectJ 切点信息的获取，见代码块9。
4.根据切点信息生成增强器，见代码块11。
代码块9：getPointcut
代码语言：javascript复制private AspectJExpressionPointcut getPointcut(Method candidateAdviceMethod, Class<?> candidateAspectClass) {
// 1.查找并返回给定方法的第一个AspectJ注解（@Before, @Around, @After, @AfterReturning, @AfterThrowing, @Pointcut）
// 因为我们之前把@Pointcut注解的方法跳过了，所以这边必然不会获取到@Pointcut注解
AspectJAnnotation<?> aspectJAnnotation =
AbstractAspectJAdvisorFactory.findAspectJAnnotationOnMethod(candidateAdviceMethod);
// 2.如果方法没有使用AspectJ的注解，则返回null
if (aspectJAnnotation == null) {
return null;
}
// 3.使用AspectJExpressionPointcut实例封装获取的信息
AspectJExpressionPointcut ajexp =
new AspectJExpressionPointcut(candidateAspectClass, new String[0], new Class<?>[0]);
// 提取得到的注解中的表达式，
// 例如：@Around("execution(* com.joonwhee.open.aop.*.*(..))")，得到：execution(* com.joonwhee.open.aop.*.*(..))
ajexp.setExpression(aspectJAnnotation.getPointcutExpression());
ajexp.setBeanFactory(this.beanFactory);
return ajexp;
}1.获取方法上的AspectJ注解，见代码块10。
代码块10：findAspectJAnnotationOnMethod
代码语言：javascript复制protected static AspectJAnnotation<?> findAspectJAnnotationOnMethod(Method method) {
// 设置要查找的注解类
Class<?>[] classesToLookFor = new Class<?>[]{
Before.class, Around.class, After.class, AfterReturning.class, AfterThrowing.class, Pointcut.class};
for (Class<?> c : classesToLookFor) {
// 查找方法上是否存在当前遍历的注解，如果有则返回
AspectJAnnotation<?> foundAnnotation = findAnnotation(method, (Class<Annotation>) c);
if (foundAnnotation != null) {
return foundAnnotation;
}
}
return null;
}代码块11：new InstantiationModelAwarePointcutAdvisorImpl
代码语言：javascript复制public InstantiationModelAwarePointcutAdvisorImpl(AspectJExpressionPointcut declaredPointcut,
Method aspectJAdviceMethod, AspectJAdvisorFactory aspectJAdvisorFactory,
MetadataAwareAspectInstanceFactory aspectInstanceFactory, int declarationOrder, String aspectName) {
// 1.简单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保存的是我们用来进行逻辑增强的方法（@Around、@After等修饰的方法）
this.aspectJAdviceMethod = aspectJAdviceMethod;
this.aspectJAdvisorFactory = aspectJAdvisorFactory;
this.aspectInstanceFactory = aspectInstanceFactory;
this.declarationOrder = declarationOrder;
this.aspectName = aspectName;
// 2.是否需要延迟实例化
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：根据注解中的信息初始化对应的增强器
this.instantiatedAdvice = instantiateAdvice(this.declaredPointcut);
}
}3.实例化增强器：根据注解中的信息初始化对应的增强器，见代码块12。
代码块12：instantiateAdvice
代码语言：javascript复制private Advice instantiateAdvice(AspectJExpressionPointcut pcut) {
return this.aspectJAdvisorFactory.getAdvice(this.aspectJAdviceMethod, pcut,
this.aspectInstanceFactory, this.declarationOrder, this.aspectName);
}
// ReflectiveAspectJAdvisorFactory.java
@Override
public Advice getAdvice(Method candidateAdviceMethod, AspectJExpressionPointcut expressionPointcut,
MetadataAwareAspectInstanceFactory aspectInstanceFactory, int declarationOrder, String aspectName) {
// 1.获取切面类
Class<?> candidateAspectClass = aspectInstanceFactory.getAspectMetadata().getAspectClass();
// 2.校验切面类（重复校验第3次...）
validate(candidateAspectClass);
// 3.查找并返回方法的第一个AspectJ注解
AspectJAnnotation<?> aspectJAnnotation =
AbstractAspectJAdvisorFactory.findAspectJAnnotationOnMethod(candidateAdviceMethod);
if (aspectJAnnotation == null) {
return null;
}
// If we get here, we know we have an AspectJ method.
// Check that it's an AspectJ-annotated class
// 4.如果我们到这里，我们知道我们有一个AspectJ方法。检查切面类是否使用了AspectJ注解
if (!isAspect(candidateAspectClass)) {
throw new AopConfigException("Advice must be declared inside an aspect type: "
"Offending method '" candidateAdviceMethod "' in class ["
candidateAspectClass.getName() "]");
}
if (logger.isDebugEnabled()) {
logger.debug("Found AspectJ method: " candidateAdviceMethod);
}
AbstractAspectJAdvice springAdvice;
// 5.根据方法使用的aspectJ注解创建对应的增强器，例如最常见的@Around注解会创建AspectJAroundAdvice
switch (aspectJAnnotation.getAnnotationType()) {
case AtBefore:
springAdvice = new AspectJMethodBeforeAdvice(
candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
break;
case AtAfter:
springAdvice = new AspectJAfterAdvice(
candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
break;
case AtAfterReturning:
springAdvice = new AspectJAfterReturningAdvice(
candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
AfterReturning afterReturningAnnotation = (AfterReturning) aspectJAnnotation.getAnnotation();
if (StringUtils.hasText(afterReturningAnnotation.returning())) {
springAdvice.setReturningName(afterReturningAnnotation.returning());
}
break;
case AtAfterThrowing:
springAdvice = new AspectJAfterThrowingAdvice(
candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
AfterThrowing afterThrowingAnnotation = (AfterThrowing) aspectJAnnotation.getAnnotation();
if (StringUtils.hasText(afterThrowingAnnotation.throwing())) {
springAdvice.setThrowingName(afterThrowingAnnotation.throwing());
}
break;
case AtAround:
springAdvice = new AspectJAroundAdvice(
candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
break;
case AtPointcut:
if (logger.isDebugEnabled()) {
logger.debug("Processing pointcut '" candidateAdviceMethod.getName() "'");
}
return null;
default:
throw new UnsupportedOperationException(
"Unsupported advice type on method: " candidateAdviceMethod);
}
// Now to configure the advice...
// 6.配置增强器
// 切面类的name，其实就是beanName
springAdvice.setAspectName(aspectName);
springAdvice.setDeclarationOrder(declarationOrder);
// 获取增强方法的参数
String[] argNames = this.parameterNameDiscoverer.getParameterNames(candidateAdviceMethod);
if (argNames != null) {
// 如果参数不为空，则赋值给springAdvice
springAdvice.setArgumentNamesFromStringArray(argNames);
}
springAdvice.calculateArgumentBindings();
// 最后，返回增强器
return springAdvice;
}代码块13：findAdvisorsThatCanApply
代码语言：javascript复制public static List<Advisor> findAdvisorsThatCanApply(List<Advisor> candidateAdvisors, Class<?> clazz) {
if (candidateAdvisors.isEmpty()) {
return candidateAdvisors;
}
List<Advisor> eligibleAdvisors = new LinkedList<Advisor>();
// 1.首先处理引介增强（@DeclareParents）用的比较少可以忽略，有兴趣的参考：https://www.cnblogs.com/HigginCui/p/6322283.html
for (Advisor candidate : candidateAdvisors) {
if (candidate instanceof IntroductionAdvisor && canApply(candidate, clazz)) {
eligibleAdvisors.add(candidate);
}
}
boolean hasIntroductions = !eligibleAdvisors.isEmpty();
// 2.遍历所有的candidateAdvisors
for (Advisor candidate : candidateAdvisors) {
// 2.1 引介增强已经处理，直接跳过
if (candidate instanceof IntroductionAdvisor) {
// already processed
continue;
}
// 2.2 正常增强处理，判断当前bean是否可以应用于当前遍历的增强器（bean是否包含在增强器的execution指定的表达式中）
if (canApply(candidate, clazz, hasIntroductions)) {
eligibleAdvisors.add(candidate);
}
}
return eligibleAdvisors;
}2.2 正常增强处理，判断当前 bean 是否可以应用于当前遍历的增强器，这边表达式判断的逻辑比较复杂，可以简单的理解为：判断 bean 是否包含在增强器的 execution 指定的表达式中。
代码块14：createProxy
代码语言：javascript复制protected Object createProxy(
Class<?> beanClass, String beanName, Object[] specificInterceptors, TargetSource targetSource) {
if (this.beanFactory instanceof ConfigurableListableBeanFactory) {
AutoProxyUtils.exposeTargetClass((ConfigurableListableBeanFactory) this.beanFactory, beanName, beanClass);
}
// 1.初始化ProxyFactory
ProxyFactory proxyFactory = new ProxyFactory();
// 从当前对象复制属性值
proxyFactory.copyFrom(this);
// 检查proxyTargetClass属性，判断对于给定的bean使用类代理还是接口代理，
// proxyTargetClass值默认为false，可以通过proxy-target-class属性设置为true
if (!proxyFactory.isProxyTargetClass()) {
// 检查preserveTargetClass属性，判断beanClass是应该基于类代理还是基于接口代理
if (shouldProxyTargetClass(beanClass, beanName)) {
// 如果是基于类代理，则将proxyTargetClass赋值为true
proxyFactory.setProxyTargetClass(true);
} else {
// 评估bean的代理接口
evaluateProxyInterfaces(beanClass, proxyFactory);
}
}
// 将拦截器封装为Advisor（advice持有者）
Advisor[] advisors = buildAdvisors(beanName, specificInterceptors);
// 将advisors添加到proxyFactory
proxyFactory.addAdvisors(advisors);
// 设置要代理的类，将targetSource赋值给proxyFactory的targetSource属性，之后可以通过该属性拿到被代理的bean的实例
proxyFactory.setTargetSource(targetSource);
// 自定义ProxyFactory，空方法，留给子类实现
customizeProxyFactory(proxyFactory);
// 用来控制proxyFactory被配置之后，是否还允许修改通知。默认值为false（即在代理被配置之后，不允许修改代理类的配置）
proxyFactory.setFrozen(this.freezeProxy);
if (advisorsPreFiltered()) {
proxyFactory.setPreFiltered(true);
}
// 2.使用proxyFactory获取代理
return proxyFactory.getProxy(getProxyClassLoader());
}2.使用 proxyFactory 获取代理，见代码块15。
代码块15：getProxy
代码语言：javascript复制public Object getProxy(ClassLoader classLoader) {
// 1.createAopProxy：创建AopProxy
// 2.getProxy(classLoader)：获取代理对象实例
return createAopProxy().getProxy(classLoader);
}1.createAopProxy：创建AopProxy，见代码块16。 2.getProxy(classLoader)：获取代理对象实例，跟我们自己写的代理类似，JDK 动态代理见代码块18，CGLIB 代理见代码块19。
代码块16：createAopProxy
代码语言：javascript复制protected final synchronized AopProxy createAopProxy() {
if (!this.active) {
// 1.激活此代理配置
activate();
}
// 2.创建AopProxy
return getAopProxyFactory().createAopProxy(this);
}
@Override
public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {
// 1.判断使用JDK动态代理还是Cglib代理
// optimize：用于控制通过cglib创建的代理是否使用激进的优化策略。除非完全了解AOP如何处理代理优化，
// 否则不推荐使用这个配置，目前这个属性仅用于cglib代理，对jdk动态代理无效
// proxyTargetClass：默认为false，设置为true时，强制使用cglib代理，设置方式：<aop:aspectj-autoproxy proxy-target-class="true" />
// hasNoUserSuppliedProxyInterfaces：config是否存在代理接口或者只有SpringProxy一个接口
if (config.isOptimize() || config.isProxyTargetClass() || hasNoUserSuppliedProxyInterfaces(config)) {
// 拿到要被代理的对象的类型
Class<?> targetClass = config.getTargetClass();
if (targetClass == null) {
// TargetSource无法确定目标类：代理创建需要接口或目标。
throw new AopConfigException("TargetSource cannot determine target class: "
"Either an interface or a target is required for proxy creation.");
}
// 要被代理的对象是接口 || targetClass是Proxy class
// 当且仅当使用getProxyClass方法或newProxyInstance方法动态生成指定的类作为代理类时，才返回true。
if (targetClass.isInterface() || Proxy.isProxyClass(targetClass)) {
// JDK动态代理，这边的入参config(AdvisedSupport)实际上是ProxyFactory对象
// 具体为：AbstractAutoProxyCreator中的proxyFactory.getProxy发起的调用，在ProxyCreatorSupport使用了this作为参数，
// 调用了的本方法，这边的this就是发起调用的proxyFactory对象，而proxyFactory对象中包含了要执行的的拦截器
return new JdkDynamicAopProxy(config);
}
// Cglib代理
return new ObjenesisCglibAopProxy(config);
} else {
// JDK动态代理
return new JdkDynamicAopProxy(config);
}
}这边创建 AopProxy 的参数 config（AdvisedSupport）实际上是代码块14中的 proxyFactory 对象。
具体为：AbstractAutoProxyCreator 中的 proxyFactory.getProxy 发起的调用，在 ProxyCreatorSupport 使用了 this 作为参数调用了本方法，这边的 this 就是发起调用的 proxyFactory对象，而 proxyFactory 对象中包含了要执行的的拦截器（Advisor）。
无论是创建 JDK 动态代理还是 CGLIB 代理，都会传入 config 参数，该参数会被保存在 advised（AdvisedSupport）变量中，见代码块17。
代码块17：JDK 动态代理、CBLIB 代理构造函数
代码语言：javascript复制// JdkDynamicAopProxy.java
public JdkDynamicAopProxy(AdvisedSupport config) throws AopConfigException {
Assert.notNull(config, "AdvisedSupport must not be null");
if (config.getAdvisors().length == 0 && config.getTargetSource() == AdvisedSupport.EMPTY_TARGET_SOURCE) {
throw new AopConfigException("No advisors and no TargetSource specified");
}
// config赋值给advised
this.advised = config;
}
// ObjenesisCglibAopProxy.java
public ObjenesisCglibAopProxy(AdvisedSupport config) {
super(config);
}
// CglibAopProxy.java
public CglibAopProxy(AdvisedSupport config) throws AopConfigException {
Assert.notNull(config, "AdvisedSupport must not be null");
if (config.getAdvisors().length == 0 && config.getTargetSource() == AdvisedSupport.EMPTY_TARGET_SOURCE) {
throw new AopConfigException("No advisors and no TargetSource specified");
}
this.advised = config;
this.advisedDispatcher = new AdvisedDispatcher(this.advised);
}代码块18：JdkDynamicAopProxy#getProxy
代码语言：javascript复制@Override
public Object getProxy(ClassLoader classLoader) {
if (logger.isDebugEnabled()) {
logger.debug("Creating JDK dynamic proxy: target source is " this.advised.getTargetSource());
}
// 1.拿到要被代理对象的所有接口
Class<?>[] proxiedInterfaces = AopProxyUtils.completeProxiedInterfaces(this.advised, true);
findDefinedEqualsAndHashCodeMethods(proxiedInterfaces);
// 2.通过classLoader、接口、InvocationHandler实现类，来获取到代理对象
return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);
}最终，通过 JDK 动态代理的类被调用时，会走到 JdkDynamicAopProxy#invoke 方法。
代码块19：CglibAopProxy#getProxy
代码语言：javascript复制@Override
public Object getProxy(ClassLoader classLoader) {
if (logger.isDebugEnabled()) {
logger.debug("Creating CGLIB proxy: target source is " this.advised.getTargetSource());
}
try {
// 1.拿到要代理目标类
Class<?> rootClass = this.advised.getTargetClass();
Assert.state(rootClass != null, "Target class must be available for creating a CGLIB proxy");
// proxySuperClass默认为rootClass
Class<?> proxySuperClass = rootClass;
if (ClassUtils.isCglibProxyClass(rootClass)) {
// 如果rootClass是被Cglib代理过的，获取rootClass的父类作为proxySuperClass
proxySuperClass = rootClass.getSuperclass();
Class<?>[] additionalInterfaces = rootClass.getInterfaces();
for (Class<?> additionalInterface : additionalInterfaces) {
// 将父类的接口也添加到advised的interfaces属性
this.advised.addInterface(additionalInterface);
}
}
// Validate the class, writing log messages as necessary.
// 2.校验proxySuperClass，主要是校验方法是否用final修饰、跨ClassLoader的包可见方法，如果有将警告写入日志
validateClassIfNecessary(proxySuperClass, classLoader);
// Configure CGLIB Enhancer...
// 3.创建和配置Cglib Enhancer
Enhancer enhancer = createEnhancer();
if (classLoader != null) {
enhancer.setClassLoader(classLoader);
if (classLoader instanceof SmartClassLoader &&
((SmartClassLoader) classLoader).isClassReloadable(proxySuperClass)) {
enhancer.setUseCache(false);
}
}
// superclass为被代理的目标类proxySuperClass，通过名字可以看出，生成的代理类实际上是继承了被代理类
enhancer.setSuperclass(proxySuperClass);
enhancer.setInterfaces(AopProxyUtils.completeProxiedInterfaces(this.advised));
enhancer.setNamingPolicy(SpringNamingPolicy.INSTANCE);
enhancer.setStrategy(new ClassLoaderAwareUndeclaredThrowableStrategy(classLoader));
// 4.获取所有要回调的拦截器
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
// 在上面调用getCallbacks之后，此时仅填充fixedInterceptorMap
enhancer.setCallbackFilter(new ProxyCallbackFilter(
this.advised.getConfigurationOnlyCopy(), this.fixedInterceptorMap, this.fixedInterceptorOffset));
enhancer.setCallbackTypes(types);
// Generate the proxy class and create a proxy instance.
// 5.生成代理类并创建代理实例，返回代理实例
return createProxyClassAndInstance(enhancer, callbacks);
} catch (CodeGenerationException ex) {
throw new AopConfigException("Could not generate CGLIB subclass of class ["
this.advised.getTargetClass() "]: "
"Common causes of this problem include using a final class or a non-visible class",
ex);
} catch (IllegalArgumentException ex) {
throw new AopConfigException("Could not generate CGLIB subclass of class ["
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);
}
}4.获取所有要回调的拦截器，见代码块20。
代码块20：getCallbacks
代码语言：javascript复制private Callback[] getCallbacks(Class<?> rootClass) throws Exception {
// Parameters used for optimization choices...
// 1.用于优化选择的参数
boolean exposeProxy = this.advised.isExposeProxy();
boolean isFrozen = this.advised.isFrozen();
boolean isStatic = this.advised.getTargetSource().isStatic();
// Choose an "aop" interceptor (used for AOP calls).
// 2.使用AdvisedSupport作为参数，创建一个DynamicAdvisedInterceptor（“aop”拦截器，用于AOP调用）
// this.advised就是之前创建CglibAopProxy时传进来的ProxyFactory(ProxyCreatorSupport子类)
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();
// 3.将aop拦截器添加到mainCallbacks中
Callback[] mainCallbacks = new Callback[]{
aopInterceptor, // for normal advice aop拦截器，因此当代理类被执行时，会走到该拦截器中
targetInterceptor, // invoke target without considering advice, if optimized
new SerializableNoOp(), // no override for methods mapped to this
targetDispatcher, this.advisedDispatcher,
new EqualsInterceptor(this.advised), // 针对equals方法的拦截器
new HashCodeInterceptor(this.advised) // 针对hashcode方法的拦截器
};
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<String, Integer>(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;
}最终，通过 CGLIB 代理的类被调用时，会走到 DynamicAdvisedInterceptor#intercept 方法。
总结
至此，创建 AOP 代理的内容已经介绍完毕。下篇文章将介绍，使用了 AOP 的方法的一次调用的完整流程。
相关文章
Spring AOP源码学习：基本概念
Spring AOP源码学习：AOP 注解的解析
