引言
上期我们对AOP核心概念及接口做了粗浅的分析，这期我们主要来探讨一下代理对象的创建过程。在开始之前，先问自己几个问题
Spring是如何帮我们去选择合适的
Advice的？找到了又是通过何种方式创建代理对象的？
好了，现在我们开始分析代理对象的创建过程，首先，先来看一下AspectJAwareAdvisorAutoProxyCreator.class类的继承体系
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可以看到AspectJAwareAdvisorAutoProxyCreator.class主要实现了这几个接口
-
AwareBean创建时注入一些容器属性等 -
BeanPostProcessorIOC 扩展点 -
AopInfrastructureBean标识此类是AOP系统类，不能被代理
这里我们仅需要关注BeanPostProcessor接口的实现，因为代理的创建是在BeanPostProcessor接口的postProcessAfterInitialization方法执行时创建的，postProcessAfterInitialization方法的具体实现逻辑是在抽象父类AbstractAutoProxyCreator中实现的
入口
上文中提到AspectJAwareAdvisorAutoProxyCreator.class是BeanPostProcessor接口的实现，现在就让我们打开它的入口源码慢慢分析
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
if (bean != null) {
// 返回用做缓存的key键
Object cacheKey = getCacheKey(bean.getClass(), beanName);
if (!this.earlyProxyReferences.contains(cacheKey)) {
return wrapIfNecessary(bean, beanName, cacheKey);
}
}
return bean;
}
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;
}
// 判断当前的Bean是否是AOP本身的系统类，是的话则跳过，不做代理操作
if (isInfrastructureClass(bean.getClass()) || shouldSkip(bean.getClass(), beanName)) {
this.advisedBeans.put(cacheKey, Boolean.FALSE);
return bean;
}
// 为该Bean找到一个合适的 advisor
Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
// 返回不为空
if (specificInterceptors != DO_NOT_PROXY) {
this.advisedBeans.put(cacheKey, Boolean.TRUE);
// 创建代理对象
Object proxy = createProxy(
bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));
this.proxyTypes.put(cacheKey, proxy.getClass());
return proxy;
}
// 没有找到合适的 advisor 则直接返回原始Bean
this.advisedBeans.put(cacheKey, Boolean.FALSE);
return bean;
}
看完wrapIfNecessary方法，这里就是创建代理对象的全过程。其实在这个方法中一共就做了两件事情:
-
getAdvicesAndAdvisorsForBean方法 筛选合适的Advisor对象，其实就是为当前目标对象找到合适的通知(Advice) -
createProxy方法 根据筛选到的切面（Advisor）集合为目标对象创建代理
下面我们分别对这两件事情作分析
寻找合适的 Advisor
findEligibleAdvisors方法是在父类AbstractAdvisorAutoProxyCreator中，
且直接调用了findEligibleAdvisors 方法
List<Advisor> advisors = findEligibleAdvisors(beanClass, beanName);
if (advisors.isEmpty()) {
return DO_NOT_PROXY;
}
return advisors.toArray();
}
protected List<Advisor> findEligibleAdvisors(Class<?> beanClass, String beanName) {
// 找到容器中的全部通知
List<Advisor> candidateAdvisors = findCandidateAdvisors();
// 筛选合适通知对象集合
List<Advisor> eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);
extendAdvisors(eligibleAdvisors);
if (!eligibleAdvisors.isEmpty()) {
eligibleAdvisors = sortAdvisors(eligibleAdvisors);
}
return eligibleAdvisors;
}
这里也是分开做了两件事情
- 首先从Spring 容器中获取到全部Advisors集合
- 执行筛选逻辑，获取符合条件的Advisors集合
找到Spring容器中全部 Advisor
这里是调用了BeanFactoryAdvisorRetrievalHelper.class的方法去获取到Spring 容器中全部Advisor集合的，这里需要注意BeanFactoryAdvisorRetrievalHelper.class类的初始化是在setBeanFactory方法中进行的
protected List<Advisor> findCandidateAdvisors() {
return this.advisorRetrievalHelper.findAdvisorBeans();
}
-
BeanFactoryAdvisorRetrievalHelper的findAdvisorBeans方法
public List<Advisor> findAdvisorBeans() {
// Determine list of advisor bean names, if not cached already.
String[] advisorNames = null;
synchronized (this) {
// 尝试从缓存中获取 Advisor 类型的Bean名称
advisorNames = this.cachedAdvisorBeanNames;
//
if (advisorNames == null) {
// 从BeanFactory中获取 Advisor 类型的全部Bean名称集合，并设置缓存
advisorNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(
this.beanFactory, Advisor.class, true, false);
this.cachedAdvisorBeanNames = advisorNames;
}
}
if (advisorNames.length == 0) {
return new LinkedList<Advisor>();
}
List<Advisor> advisors = new LinkedList<Advisor>();
// 遍历 Advisor类型 BeanName 集合
for (String name : advisorNames) {
// 判断是否合法，这里返回都是true
if (isEligibleBean(name)) {
// 判断该Bean是否正在创建中，创建中则直接跳过
if (this.beanFactory.isCurrentlyInCreation(name)) {
if (logger.isDebugEnabled()) {
logger.debug("Skipping currently created advisor '" + name + "'");
}
}
else {
try {
// 根据BeanName和Advisor类型从BeanFactory中获取Bean
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;
}
}
}
}
return advisors;
}
findAdvisorBeans方法的的目的非常明确，就是找到容器中全部的Advisor
- 先尝试从缓存中获取
Advisor集合 - 缓存中不存在，则执行获取逻辑
- 获取到了所有类型为
Advisor的Bean的名称 - 根据获取到的BeanName获取Bean
- 获取到了所有类型为
为当前Bean匹配合适的 Advisor
在以上的步骤中，我们已经拿到了容器中所有的Advisor对象集合，也就是说我们已经拿到了容器中所有已配置的AOP切面。接下里的事情就是为当前的目标对象筛选出适合的Advisor集合，现在我们开始分析AbstractAdvisorAutoProxyCreator.class的findAdvisorsThatCanApply方法
protected List<Advisor> findAdvisorsThatCanApply(
List<Advisor> candidateAdvisors, Class<?> beanClass, String beanName) {
ProxyCreationContext.setCurrentProxiedBeanName(beanName);
try {
// 调用 AopUtils.findAdvisorsThatCanApply 为当前Bean筛选合适的 Advisor
return AopUtils.findAdvisorsThatCanApply(candidateAdvisors, beanClass);
}
finally {
ProxyCreationContext.setCurrentProxiedBeanName(null);
}
}
findAdvisorsThatCanApply方法里调用了工具类AOPUtils的findAdvisorsThatCanApply方法
public static List<Advisor> findAdvisorsThatCanApply(List<Advisor> candidateAdvisors, Class<?> clazz) {
if (candidateAdvisors.isEmpty()) {
return candidateAdvisors;
}
List<Advisor> eligibleAdvisors = new LinkedList<Advisor>();
// 先找出 IntroductionAdvisor 类型的Advisor
for (Advisor candidate : candidateAdvisors) {
if (candidate instanceof IntroductionAdvisor && canApply(candidate, clazz)) {
eligibleAdvisors.add(candidate);
}
}
boolean hasIntroductions = !eligibleAdvisors.isEmpty();
// 再从余下的Advisor中继续匹配
for (Advisor candidate : candidateAdvisors) {
if (candidate instanceof IntroductionAdvisor) {
// already processed
continue;
}
if (canApply(candidate, clazz, hasIntroductions)) {
eligibleAdvisors.add(candidate);
}
}
return eligibleAdvisors;
}
以上代码逻辑会先筛选出IntroductionAdvisor类型的Advisor，再筛选余下的其他Advisor
public static boolean canApply(Advisor advisor, Class<?> targetClass) {
return canApply(advisor, targetClass, false);
}
public static boolean canApply(Advisor advisor, Class<?> targetClass, boolean hasIntroductions) {
if (advisor instanceof IntroductionAdvisor) {
return ((IntroductionAdvisor) advisor).getClassFilter().matches(targetClass);
}
else if (advisor instanceof PointcutAdvisor) {
PointcutAdvisor pca = (PointcutAdvisor) advisor;
return canApply(pca.getPointcut(), targetClass, hasIntroductions);
}
else {
// It doesn't have a pointcut so we assume it applies.
return true;
}
}
public static boolean canApply(Pointcut pc, Class<?> targetClass, boolean hasIntroductions) {
Assert.notNull(pc, "Pointcut must not be null");
// 先判断类型是否匹配
if (!pc.getClassFilter().matches(targetClass)) {
return false;
}
// 获取切点方法匹配器
MethodMatcher methodMatcher = pc.getMethodMatcher();
if (methodMatcher == MethodMatcher.TRUE) {
// No need to iterate the methods if we're matching any method anyway...
return true;
}
IntroductionAwareMethodMatcher introductionAwareMethodMatcher = null;
if (methodMatcher instanceof IntroductionAwareMethodMatcher) {
introductionAwareMethodMatcher = (IntroductionAwareMethodMatcher) methodMatcher;
}
Set<Class<?>> classes = new LinkedHashSet<Class<?>>(ClassUtils.getAllInterfacesForClassAsSet(targetClass));
classes.add(targetClass);
for (Class<?> clazz : classes) {
// 获取当前目标class的所有方法
Method[] methods = ReflectionUtils.getAllDeclaredMethods(clazz);
for (Method method : methods) {
// 调用 methodMatcher.matches 判断当前方法是否匹配该切点
if ((introductionAwareMethodMatcher != null &&
introductionAwareMethodMatcher.matches(method, targetClass, hasIntroductions)) ||
methodMatcher.matches(method, targetClass)) {
return true;
}
}
}
return false;
}
canApply是用于筛选核心方法，在上期分析连接点Pointcut接口时，我们知道Pointcut持有ClassFilter和MethodMatcher对象，具体的筛选逻辑就是由它们完成的，至于在它们具体的macthes方法是是如何实现筛选的，这里我也没有进行过深入分析，感兴趣的可以在其实现类AspectJExpressionPointcut.class中继续查看
生成代理对象
在上文的分析结束后，我们已经筛选出来了合适的 Advisor，Advisor持有Advice(通知)，接下来的操作就是根据我们配置的Advice为目标对象创建代理对象了
protected Object createProxy(
Class<?> beanClass, String beanName, Object[] specificInterceptors, TargetSource targetSource) {
if (this.beanFactory instanceof ConfigurableListableBeanFactory) {
AutoProxyUtils.exposeTargetClass((ConfigurableListableBeanFactory) this.beanFactory, beanName, beanClass);
}
// 首先创建一个代理创建工厂类，之后的操作都是为此工厂配置属性
ProxyFactory proxyFactory = new ProxyFactory();
proxyFactory.copyFrom(this);
// 判断配置属性proxy-target-class 是否等于False
if (!proxyFactory.isProxyTargetClass()) {
// 判断目标 BeanDefinition是否配置preserveTargetClass 为 ture，是的话配置CGLIB动态代理
if (shouldProxyTargetClass(beanClass, beanName)) {
proxyFactory.setProxyTargetClass(true);
}
else {
// 设置目标类接口到proxyFactory，如果没有实现接口则使用CGLIB代理
evaluateProxyInterfaces(beanClass, proxyFactory);
}
}
Advisor[] advisors = buildAdvisors(beanName, specificInterceptors);
// proxyFactory 设置 advisors
proxyFactory.addAdvisors(advisors);
// 设置目标对象资源
proxyFactory.setTargetSource(targetSource);
customizeProxyFactory(proxyFactory);
proxyFactory.setFrozen(this.freezeProxy);
if (advisorsPreFiltered()) {
proxyFactory.setPreFiltered(true);
}
// 创建代理
return proxyFactory.getProxy(getProxyClassLoader());
创建代理对象前，会新建一个代理工厂创建类，并为此工厂类配置相关属性，例如proxy-target-class的配置，虽然默认配置是false会使用JDK动态代理，但如果没有实现接口，也会自动设置proxy-target-class为true使用CGLIB创建代理对象
完成ProxyFactory的配置之后，就可以通过它创建代理对象了
/**
* 创建代理对象
*/
public Object getProxy(ClassLoader classLoader) {
return createAopProxy().getProxy(classLoader);
}
调用父类ProxyCreatorSupport的createAopProxy方法，获取到代理创建工厂，工厂类(DefaultAopProxyFactory)是在父类的构造方法中创建的
protected final synchronized AopProxy createAopProxy() {
if (!this.active) {
activate();
}
// 获取代理创建工厂类 （DefaultAopProxyFactory.class）创建代理对象
return getAopProxyFactory().createAopProxy(this);
}
最终在DefaultAopProxyFactory工厂类createAopProxy中创建代理对象
public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {
// 这里主要是判断 proxy-target-class 属性是否为true。默认是false
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)) {
return new JdkDynamicAopProxy(config);
}
// 使用CGLIB动态代理
return new ObjenesisCglibAopProxy(config);
}
else {
// 默认使用JDK动态打理
return new JdkDynamicAopProxy(config);
}
}
最终的代理的创建是在ObjenesisCglibAopProxy或JdkDynamicAopProxy中完成的，至于更具体的创建逻辑，因为这一系列的源码分析只是为了能够对AOP的整体逻辑有清晰的认识，所以这里就不做更详细的分析了。
尾言
本篇文章分析了AOP代理创建的整个过程，纵观整篇文章，篇幅有限，其中还有很多的点没有详细展开分析，只是粗略的分析了AOP代理的创建过程，惭愧 ... 。分析有误的地方，希望大家可以指出。
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