spring源码分析-AOP
前期回顾
spring源码分析-IOC
spring源码分析-DI
在spring中，AOP是使用动态代理来实现的，那么，要想实现此功能，就必须在实例化之后，依赖注入之前，对类进行动态代理，然后将经过代理之后的bean注入到所依赖的对象中
在spring中，bean动态代理的入口是一个spring的扩展点
BeanPostProcessor,而这个扩展点就是在AbstractAutowireCapableBeanFactory这个类调用initializeBean来完成的
protected Object initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd) {
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction在这个方法中有调用了
applyBeanPostProcessorsAfterInitialization，意思就是当bean初始化完成后，调用
public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
throws BeansException {
Object result = existingBean;
for (BeanPostProcessor processor : getBeanPostProcessors()) {
Object current = processor.postProcessAfterInitialization(result, beanName);
if (current == null) {
return result;
}
result = current;
}
return result;
}
在这个方法中，我们终于看到了梦寐以求的方法
BeanPostProcessor,并且调用了BeanPostProcessor的postProcessAfterInitialization方法。
spring就是通过这个扩展点来进行bean的代理的
public Object postProcessAfterInitialization(@Nullable Object bean, String beanName) {
if (bean != null) {
Object cacheKey = this.getCacheKey(bean.getClass(), beanName);
if (this.earlyProxyReferences.remove(cacheKey) != bean) {
// 对bean进行包装，并创建代理类
return this.wrapIfNecessary(bean, beanName, cacheKey);
}
}
return bean;
}
protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
if (StringUtils.hasLength(beanName) && this.targetSourcedBeans.contains(beanName)) {
return bean;
} else if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) {
return bean;
} else if (!this.isInfrastructureClass(bean.getClass()) && !this.shouldSkip(bean.getClass(), beanName)) {
Object[] specificInterceptors = this.getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, (TargetSource)null);
if (specificInterceptors != DO_NOT_PROXY) {
this.advisedBeans.put(cacheKey, Boolean.TRUE);
// 创建代理类
Object proxy = this.createProxy(bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));
this.proxyTypes.put(cacheKey, proxy.getClass());
return proxy;
} else {
this.advisedBeans.put(cacheKey, Boolean.FALSE);
return bean;
}
} else {
this.advisedBeans.put(cacheKey, Boolean.FALSE);
return bean;
}
}
在这里，我们找到了创建proxy代理类的方法
protected Object createProxy(Class beanClass, @Nullable String beanName, @Nullable Object[] specificInterceptors, TargetSource targetSource) {
if (this.beanFactory instanceof ConfigurableListableBeanFactory) {
AutoProxyUtils.exposeTargetClass((ConfigurableListableBeanFactory)this.beanFactory, beanName, beanClass);
}
ProxyFactory proxyFactory = new ProxyFactory();
proxyFactory.copyFrom(this);
if (!proxyFactory.isProxyTargetClass()) {
if (this.shouldProxyTargetClass(beanClass, beanName)) {
proxyFactory.setProxyTargetClass(true);
} else {
this.evaluateProxyInterfaces(beanClass, proxyFactory);
}
}
Advisor[] advisors = this.buildAdvisors(beanName, specificInterceptors);
proxyFactory.addAdvisors(advisors);
proxyFactory.setTargetSource(targetSource);
this.customizeProxyFactory(proxyFactory);
proxyFactory.setFrozen(this.freezeProxy);
if (this.advisorsPreFiltered()) {
proxyFactory.setPreFiltered(true);
}
// 根据代理工厂获取代理类
return proxyFactory.getProxy(this.getProxyClassLoader());
}
在这个方法的最后，我们找到了获取代理类的方法
getProxy
public Object getProxy(@Nullable ClassLoader classLoader) {
return this.createAopProxy().getProxy(classLoader);
}
这个地方又是一个策略模式，在spring中有两种实现，一种是
cglib，一种是jdk proxy,当我们定义的类实现了接口时，spring会使用JdkDynamicAopProxy,否则便会使用CglibAopProxy,当然，我们也可以通过配置文件制定代理方式，例如设置proxy=true,强制使用cglib进行代理
我们已
JDK代理为例，接着往下分析
public Object getProxy(@Nullable ClassLoader classLoader) {
if (logger.isTraceEnabled()) {
logger.trace("Creating JDK dynamic proxy: " + this.advised.getTargetSource());
}
Class[] proxiedInterfaces = AopProxyUtils.completeProxiedInterfaces(this.advised, true);
this.findDefinedEqualsAndHashCodeMethods(proxiedInterfaces);
return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);
}
在这里，我们看到了非常熟悉的代码
Proxy.newProxyInstance(classLoader, proxiedInterfaces, this)，这是我们非常熟悉的JDK代理的写法，那么代理类调用会走到哪里呢，这个方法中，最后一个参数传的是this，也就是在调用时会调用JdkDynamicAopProxy的invoke方法
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
Object oldProxy = null;
boolean setProxyContext = false;
TargetSource targetSource = this.advised.targetSource;
Object target = null;
try {
// 调用equals方法，直接调用equals，不用动态代理
if (!this.equalsDefined && AopUtils.isEqualsMethod(method)) {
// The target does not implement the equals(Object) method itself.
return equals(args[0]);
}
// 调用hashCode方法，直接调用hashCode，不用动态代理
else if (!this.hashCodeDefined && AopUtils.isHashCodeMethod(method)) {
// The target does not implement the hashCode() method itself.
return hashCode();
}
else if (method.getDeclaringClass() == DecoratingProxy.class) {
// There is only getDecoratedClass() declared -> dispatch to proxy config.
return AopProxyUtils.ultimateTargetClass(this.advised);
}
else if (!this.advised.opaque && method.getDeclaringClass().isInterface() &&
method.getDeclaringClass().isAssignableFrom(Advised.class)) {
// Service invocations on ProxyConfig with the proxy config...
return AopUtils.invokeJoinpointUsingReflection(this.advised, method, args);
}
Object retVal;
if (this.advised.exposeProxy) {
// Make invocation available if necessary.
oldProxy = AopContext.setCurrentProxy(proxy);
setProxyContext = true;
}
// Get as late as possible to minimize the time we "own" the target,
// in case it comes from a pool.
target = targetSource.getTarget();
Class targetClass = (target != null ? target.getClass() : null);
// Get the interception chain for this method.
// 在AOP中使用责任链模式，来形成一个调用链
List在动态代理调用时，spring会将相应的切换封装成一个list，并通过责任链模式将AOP拦截形成一个链，以达到AOP的动态扩展，实现解耦
public Object proceed() throws Throwable {
// We start with an index of -1 and increment early.
if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) {
return invokeJoinpoint();
}
Object interceptorOrInterceptionAdvice =
this.interceptorsAndDynamicMethodMatchers.get(++this.currentInterceptorIndex);
if (interceptorOrInterceptionAdvice instanceof InterceptorAndDynamicMethodMatcher) {
// Evaluate dynamic method matcher here: static part will already have
// been evaluated and found to match.
InterceptorAndDynamicMethodMatcher dm =
(InterceptorAndDynamicMethodMatcher) interceptorOrInterceptionAdvice;
Class targetClass = (this.targetClass != null ? this.targetClass : this.method.getDeclaringClass());
if (dm.methodMatcher.matches(this.method, targetClass, this.arguments)) {
// 调用相应的前置通知，后置通知等
return dm.interceptor.invoke(this);
}
else {
// Dynamic matching failed.
// Skip this interceptor and invoke the next in the chain.
return proceed();
}
}
else {
// It's an interceptor, so we just invoke it: The pointcut will have
// been evaluated statically before this object was constructed.
return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);
}
}
前置通知
MethodBeforeAdviceInterceptor
public Object invoke(MethodInvocation mi) throws Throwable {
this.advice.before(mi.getMethod(), mi.getArguments(), mi.getThis());
return mi.proceed();
}
后置通知
AspectJAfterAdvice
public Object invoke(MethodInvocation mi) throws Throwable {
try {
return mi.proceed();
}
finally {
invokeAdviceMethod(getJoinPointMatch(), null, null);
}
}
返回通知
AfterReturningAdviceInterceptor
public Object invoke(MethodInvocation mi) throws Throwable {
Object retVal = mi.proceed();
this.advice.afterReturning(retVal, mi.getMethod(), mi.getArguments(), mi.getThis());
return retVal;
}
异常通知
AspectJAfterThrowingAdvice
public Object invoke(MethodInvocation mi) throws Throwable {
try {
return mi.proceed();
}
catch (Throwable ex) {
if (shouldInvokeOnThrowing(ex)) {
invokeAdviceMethod(getJoinPointMatch(), null, ex);
}
throw ex;
}
}
环绕通知
AspectJAroundAdvice
public Object invoke(MethodInvocation mi) throws Throwable {
if (!(mi instanceof ProxyMethodInvocation)) {
throw new IllegalStateException("MethodInvocation is not a Spring ProxyMethodInvocation: " + mi);
}
ProxyMethodInvocation pmi = (ProxyMethodInvocation) mi;
ProceedingJoinPoint pjp = lazyGetProceedingJoinPoint(pmi);
JoinPointMatch jpm = getJoinPointMatch(pmi);
return invokeAdviceMethod(pjp, jpm, null, null);
}
spring通过一种十分巧妙的方式，将所有的拦截串成一个链，通过这种方式，完美的实现了程序的解耦
最后，还是附上这个过程的时序图，小伙伴么可以根据时序图再自己跟一下源码
