【源码】按照自己的思路研究Spring AOP源码 ①
一个例子
// 定义一个切面
package cn.eagle.li.source.aspect;
@Component
@Aspect
public class ServiceAspect {
@Pointcut("execution(* cn.eagle.li.source.service.*.*(..))")
public void pointCut() {
}
@Before("pointCut()")
public void methodBefore() {
System.out.println("===== Before =====");
}
@After("pointCut()")
public void methodAfter() {
System.out.println("===== After =====");
}
@AfterReturning("pointCut()")
public void methodReturn() {
System.out.println("===== AfterReturning =====");
}
@Around("pointCut()")
public void doAround(ProceedingJoinPoint pjp) throws Throwable {
System.out.println("===== Around before =====");
pjp.proceed();
System.out.println("===== Around after =====");
}
}
// 一个接口
package cn.eagle.li.source.service;
public interface IService {
void doService();
}
// 一个实现类
package cn.eagle.li.source.service.impl;
@Service
public class ServiceImpl implements IService {
@Override
public void doService() {
System.out.println("do service");
}
}
// Main类
@Configuration
@ComponentScan(basePackages = {"cn.eagle.li.source"})
@EnableAspectJAutoProxy(exposeProxy = true)
public class Main {
public static void main(String[] args) {
AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(Main.class);
IService service = context.getBean(IService.class);
service.doService();
}
}
执行结果如下：
===== Around before =====
===== Before =====
do service
===== AfterReturning =====
===== After =====
===== Around after =====
从@EnableAspectJAutoProxy注解入手
下面是EnableAspectJAutoProxy注解类内容
@Import(AspectJAutoProxyRegistrar.class)
public @interface EnableAspectJAutoProxy {
//代理的实现方式，true为CGLIB, false为JDK，默认false
boolean proxyTargetClass() default false;
// 要不要暴露代理对象
boolean exposeProxy() default false;
}
除了上面两个参数比较重要外，它还有一个Import注解，在Spring中，只要一种注解组合了另一种注解，它就具有该注解的功能，也就是这个注解拥有了@Import注解的功能。
@Import(AspectJAutoProxyRegistrar.class)
我们看到它import了AspectJAutoProxyRegistrar这个类，我们下面再看看这个类的内容，发现它主要的工作就是注册一个name为：
org.springframework.aop.config.internalAutoProxyCreator，类为AnnotationAwareAspectJAutoProxyCreator的BeanDefinition。
class AspectJAutoProxyRegistrar implements ImportBeanDefinitionRegistrar {
@Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
AopConfigUtils.registerAspectJAnnotationAutoProxyCreatorIfNecessary(registry);
// ......
}
}
AopConfigUtils.registerAspectJAnnotationAutoProxyCreatorIfNecessary(registry);
public abstract class AopConfigUtils {
@Nullable
public static BeanDefinition registerAspectJAnnotationAutoProxyCreatorIfNecessary(
BeanDefinitionRegistry registry, @Nullable Object source) {
return registerOrEscalateApcAsRequired(AnnotationAwareAspectJAutoProxyCreator.class, registry, source);
}
}
public abstract class AopConfigUtils {
public static final String AUTO_PROXY_CREATOR_BEAN_NAME =
"org.springframework.aop.config.internalAutoProxyCreator";
@Nullable
private static BeanDefinition registerOrEscalateApcAsRequired(
Class<?> cls, BeanDefinitionRegistry registry, @Nullable Object source) {
Assert.notNull(registry, "BeanDefinitionRegistry must not be null");
if (registry.containsBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME)) {
BeanDefinition apcDefinition = registry.getBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME);
if (!cls.getName().equals(apcDefinition.getBeanClassName())) {
int currentPriority = findPriorityForClass(apcDefinition.getBeanClassName());
int requiredPriority = findPriorityForClass(cls);
if (currentPriority < requiredPriority) {
apcDefinition.setBeanClassName(cls.getName());
}
}
return null;
}
RootBeanDefinition beanDefinition = new RootBeanDefinition(cls);
beanDefinition.setSource(source);
beanDefinition.getPropertyValues().add("order", Ordered.HIGHEST_PRECEDENCE);
beanDefinition.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
// 注册 BeanDefinition
// AUTO_PROXY_CREATOR_BEAN_NAME = org.springframework.aop.config.internalAutoProxyCreator
// beanDefinition = AnnotationAwareAspectJAutoProxyCreator.class
registry.registerBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME, beanDefinition);
return beanDefinition;
}
}
此时有一个疑问：那就是什么时候调用这个方法来加载AnnotationAwareAspectJAutoProxyCreator这个类的BeanDefinition呢？
从下面这张图可以看到是在容器进行刷新的时候，调用invokeBeanFactoryPostProcessors这个方法来进行执行的，具体的执行过程就不展开了。
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
StartupStep contextRefresh = this.applicationStartup.start("spring.context.refresh");
// Prepare this context for refreshing.
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);
StartupStep beanPostProcess = this.applicationStartup.start("spring.context.beans.post-process");
// Invoke factory processors registered as beans in the context.
// 在这里把beandefinition加载
invokeBeanFactoryPostProcessors(beanFactory);
// ......
}
}
现在这个类的BeanDefinition准备好了，那什么时候会创建AnnotationAwareAspectJAutoProxyCreator这个实例，然后加载到容器里呢？
我们看一下这个类的继承关系，发现它是一个实现了BeanPostProcessor接口，也就是说它是一个后置处理器。在refresh()方法中有一个步骤是专门用来注册后置处理器的，也就是registerBeanPostProcessors()这个方法。
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
StartupStep contextRefresh = this.applicationStartup.start("spring.context.refresh");
// Prepare this context for refreshing.
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);
StartupStep beanPostProcess = this.applicationStartup.start("spring.context.beans.post-process");
// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
// 在这里把BeanPostProcessor加载到容器中
registerBeanPostProcessors(beanFactory);
// ......
}
}
在调试的过程中，发现在PostProcessorRegistrationDelegate这个类下的registerBeanPostProcessors()这个方法下会创建AnnotationAwareAspectJAutoProxyCreator，并把它注册到容器中，如下图。
PostProcessorRegistrationDelegate类下
public static void registerBeanPostProcessors(
ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {
}
经过上面的一个讨论，我总结了一下它的一些关键触发路径，如下：
refresh() -> invokeBeanFactoryPostProcessors() -> AspectJAutoProxyRegistrar.registerBeanDefinitions()
name:"org.springframework.aop.config.internalAutoProxyCreator" beanDefinition:AnnotationAwareAspectJAutoProxyCreator -> registerBeanPostProcessors() -> 创建类实例并加载到容器中
什么时候会创建代理对象？
容器里有了AnnotationAwareAspectJAutoProxyCreator这个实例，它具体有什么用呢，它什么时候会生成代理对象呢？
protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
invokeAwareMethods(beanName, bean);
return null;
}, getAccessControlContext());
}
else {
invokeAwareMethods(beanName, bean);
}
Object wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}
try {
invokeInitMethods(beanName, wrappedBean, mbd);
}
catch (Throwable ex) {
throw new BeanCreationException(
(mbd != null ? mbd.getResourceDescription() : null),
beanName, "Invocation of init method failed", ex);
}
if (mbd == null || !mbd.isSynthetic()) {
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
return wrappedBean;
}
大家都知道，Spring在创建一个类实例后，会对这个类进行初始化，然后会执行一系列的后置处理器，就在applyBeanPostProcessorsAfterInitialization()这个方法里面。
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
它会依次地去调用每一个后置处理器，当然也包括了我们刚刚注册的AnnotationAwareAspectJAutoProxyCreator这个后置处理器，具体的执行方法就是postProcessAfterInitialization();
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;
}
我们来看一下AnnotationAwareAspectJAutoProxyCreator类的postProcessAfterInitialization这个方法，发现如果没有包装过，就把它包装一下。
public Object postProcessAfterInitialization(@Nullable Object bean, String beanName) {
if (bean != null) {
Object cacheKey = getCacheKey(bean.getClass(), beanName);
if (this.earlyProxyReferences.remove(cacheKey) != bean) {
return wrapIfNecessary(bean, beanName, cacheKey);
}
}
return bean;
}
return wrapIfNecessary(bean, beanName, cacheKey);
我们看到它会获取一些适配这个类的Advices和Advisors，如果不为null，就创建一个代理对象。
protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
if (StringUtils.hasLength(beanName) && 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.
Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
// DO_NOT_PROXY = null;
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;
}
this.advisedBeans.put(cacheKey, Boolean.FALSE);
return bean;
}
Object proxy = createProxy(
bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));
protected Object createProxy(Class<?> beanClass, @Nullable String beanName,
@Nullable Object[] specificInterceptors, TargetSource targetSource) {
// ......
return proxyFactory.getProxy(targetClassLoader);
}
public Object getProxy(@Nullable ClassLoader classLoader) {
return createAopProxy().getProxy(classLoader);
}
Spring AOP有两种代理类，Jdk代理类和Cglib代理类，具体要看proxyTargetClass这个配置项和这个类是否实现了接口。
public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {
if (!NativeDetector.inNativeImage() &&
(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.");
}
// 如果目标类是一个接口 || 或者目标类是一个代理类
if (targetClass.isInterface() || Proxy.isProxyClass(targetClass)) {
return new JdkDynamicAopProxy(config);
}
return new ObjenesisCglibAopProxy(config);
}
else {
return new JdkDynamicAopProxy(config);
}
}
我们以JDK动态代理为例，发现它就是用Java的api进行创建的，代理类JdkDynamicAopProxy这个类
final class JdkDynamicAopProxy implements AopProxy, InvocationHandler, Serializable {
@Override
public Object getProxy(@Nullable ClassLoader classLoader) {
if (logger.isTraceEnabled()) {
logger.trace("Creating JDK dynamic proxy: " + this.advised.getTargetSource());
}
return Proxy.newProxyInstance(classLoader, this.proxiedInterfaces, this);
}
}
到现在，我们知道，当创建一个bean实例后，在它初始化后，会调用每个后置处理器的初始化后的方法
当调用AOP的后置处理器的时候，会根据有没有适配它的advice和advitor来创建代理类
创建代理类的时候，有两种选择，一是JDK代理类，二是Cglib代理类
如果proxyTargetClass为true或者这个类没有实现接口的话，就选择Cglib代理类，否则选择JDK代理类。
方法执行时怎么实现拦截的？
现在我们获取一个bean时，获取的就是它的代理类，那在调用其方法时，那些符合的通知是怎么一步步执行的呢？
我们以JDK代理类为例，我们都知道，在JDK动态代理中，实际执行的时候是执行的代理类的invoke方法，所以看一下它的具体内容：
final class JdkDynamicAopProxy implements AopProxy, InvocationHandler, Serializable {
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 {
if (!this.equalsDefined && AopUtils.isEqualsMethod(method)) {
// The target does not implement the equals(Object) method itself.
return equals(args[0]);
}
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;
// 如果设置了exposeProxy参数
// 这里暴露了代理对象
// AopContext.currentProxy() 获得
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.
List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);
// Check whether we have any advice. If we don't, we can fallback on direct
// reflective invocation of the target, and avoid creating a MethodInvocation.
if (chain.isEmpty()) {
// 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 = AopUtils.invokeJoinpointUsingReflection(target, method, argsToUse);
}
else {
// We need to create a method invocation...
MethodInvocation invocation =
new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain);
// Proceed to the joinpoint through the interceptor chain.
retVal = invocation.proceed();
}
// Massage return value if necessary.
Class<?> returnType = method.getReturnType();
if (retVal != null && retVal == target &&
returnType != Object.class && returnType.isInstance(proxy) &&
!RawTargetAccess.class.isAssignableFrom(method.getDeclaringClass())) {
// Special case: it returned "this" and the return type of the method
// is type-compatible. Note that we can't help if the target sets
// a reference to itself in another returned object.
retVal = proxy;
}
else if (retVal == null && returnType != Void.TYPE && returnType.isPrimitive()) {
throw new AopInvocationException(
"Null return value from advice does not match primitive return type for: " + method);
}
return retVal;
}
finally {
if (target != null && !targetSource.isStatic()) {
// Must have come from TargetSource.
targetSource.releaseTarget(target);
}
if (setProxyContext) {
// Restore old proxy.
AopContext.setCurrentProxy(oldProxy);
}
}
}
}
总的看下来，主要关心以下内容：
// 如果设置了exposeProxy参数
// 这里暴露了代理对象
// AopContext.currentProxy() 获得
if (this.advised.exposeProxy) {
// Make invocation available if necessary.
// 这里是用ThreadLocal实现的
oldProxy = AopContext.setCurrentProxy(proxy);
setProxyContext = true;
}
// 创建拦截器链
List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);
if (chain.isEmpty()) {
Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
// 直接执行本方法
retVal = AopUtils.invokeJoinpointUsingReflection(target, method, argsToUse);
}
else {
MethodInvocation invocation =
new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain);
retVal = invocation.proceed();
}
这个执行链就是一个数组，然后一个一个向下执行，根据之前的例子，这个生成的执行链如下：
AspectJAroundAdvice MethodBeforeAdviceInterceptor AspectJAfterAdvice AspectJAfterReturningAdvice
最终包装成ReflectiveMethodInvocation这个类，调用其proceed()方法执行，如下：
public class ReflectiveMethodInvocation implements ProxyMethodInvocation, Cloneable {
public Object proceed() throws Throwable {
// 拦截器链中的最后一个拦截器执行完
if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) {
// 执行目标方法
return invokeJoinpoint();
}
// 每次执行新的拦截器，下标+1
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)) {
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.
// 上面的例子每次都会这个方法
return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);
}
}
}
public class AspectJAroundAdvice extends AbstractAspectJAdvice implements MethodInterceptor, Serializable {
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);
// 调用通知的方法
return invokeAdviceMethod(pjp, jpm, null, null);
}
}
public class MethodBeforeAdviceInterceptor implements MethodInterceptor, BeforeAdvice, Serializable {
public Object invoke(MethodInvocation mi) throws Throwable {
// 调用通知方法
this.advice.before(mi.getMethod(), mi.getArguments(), mi.getThis());
// 下一个拦截器
return mi.proceed();
}
}
public class AspectJAfterAdvice extends AbstractAspectJAdvice
implements MethodInterceptor, AfterAdvice, Serializable {
public Object invoke(MethodInvocation mi) throws Throwable {
try {
// 下一个拦截器
return mi.proceed();
}
finally {
// 调用通知方法
invokeAdviceMethod(getJoinPointMatch(), null, null);
}
}
}
public class AfterReturningAdviceInterceptor implements MethodInterceptor, AfterAdvice, Serializable {
implements MethodInterceptor, AfterAdvice, Serializable {
public Object invoke(MethodInvocation mi) throws Throwable {
// 下一个拦截器
Object retVal = mi.proceed();
// 调用通知方法
this.advice.afterReturning(retVal, mi.getMethod(), mi.getArguments(), mi.getThis());
return retVal;
}
}
===== Around before =====
===== Before =====
do service
===== AfterReturning =====
===== After =====
===== Around after =====
从上面可以看出，代理类执行的时候，就是将符合的advice排序得到一个数组，然后依次的进行执行。
总结
- 从EnableAspectJAutoProxy注解入手，Spring会注册AnnotationAwareAspectJAutoProxyCreator这个类
- AnnotationAwareAspectJAutoProxyCreator是个BeanPostProcessor，在初始化后，会调用后置处理器，生成代理对象
- 在类执行方法时，会根据通知生成一个拦截器数组，然后将所有相关的通知一个一个的执行
问题
我们看到上面的通知顺序是： AspectJAroundAdvice MethodBeforeAdviceInterceptor AspectJAfterAdvice AspectJAfterReturningAdvice
但是网上有好多文章都说的顺序是这样的：AspectJAfterReturningAdvice AspectJAfterAdvice AspectJAroundAdvice MethodBeforeAdviceInterceptor
不同的执行顺序会对你的程序会有不同的影响
后续将会写一篇文章专门介绍这个原因
