一、Spring异步调用底层原理
开启异步调用只需一个注解@EnableAsync
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(AsyncConfigurationSelector.class)
public @interface EnableAsync { /**
* Indicate the 'async' annotation type to be detected at either class
* or method level.
* <p>By default, both Spring's @{@link Async} annotation and the EJB 3.1
* {@code @javax.ejb.Asynchronous} annotation will be detected.
* <p>This attribute exists so that developers can provide their own
* custom annotation type to indicate that a method (or all methods of
* a given class) should be invoked asynchronously.
*/
Class<? extends Annotation> annotation() default Annotation.class; /**
* Indicate whether subclass-based (CGLIB) proxies are to be created as opposed
* to standard Java interface-based proxies.
* <p><strong>Applicable only if the {@link #mode} is set to {@link AdviceMode#PROXY}</strong>.
* <p>The default is {@code false}.
* <p>Note that setting this attribute to {@code true} will affect <em>all</em>
* Spring-managed beans requiring proxying, not just those marked with {@code @Async}.
* For example, other beans marked with Spring's {@code @Transactional} annotation
* will be upgraded to subclass proxying at the same time. This approach has no
* negative impact in practice unless one is explicitly expecting one type of proxy
* vs. another — for example, in tests.
*/
boolean proxyTargetClass() default false; /**
* Indicate how async advice should be applied.
* <p><b>The default is {@link AdviceMode#PROXY}.</b>
* Please note that proxy mode allows for interception of calls through the proxy
* only. Local calls within the same class cannot get intercepted that way; an
* {@link Async} annotation on such a method within a local call will be ignored
* since Spring's interceptor does not even kick in for such a runtime scenario.
* For a more advanced mode of interception, consider switching this to
* {@link AdviceMode#ASPECTJ}.
*/
AdviceMode mode() default AdviceMode.PROXY; /**
* Indicate the order in which the {@link AsyncAnnotationBeanPostProcessor}
* should be applied.
* <p>The default is {@link Ordered#LOWEST_PRECEDENCE} in order to run
* after all other post-processors, so that it can add an advisor to
* existing proxies rather than double-proxy.
*/
int order() default Ordered.LOWEST_PRECEDENCE; }
AsyncConfigurationSelector的作用是从两个异步配置类中选择一个来完成底层异步代理的工作。这个两个配置类分别是AspectJAsyncConfiguration、ProxyAsyncConfiguration。
@Override
@Nullable
public String[] selectImports(AdviceMode adviceMode) {
switch (adviceMode) {
case PROXY:
return new String[] {ProxyAsyncConfiguration.class.getName()};
case ASPECTJ:
return new String[] {ASYNC_EXECUTION_ASPECT_CONFIGURATION_CLASS_NAME};
default:
return null;
}
}
其中adviceMode就是@EnableAsync注解中mode()方法的值，默认是"PROXY"。接下来着重看一下ProxyAsyncConfiguration做了哪些事情。
@Configuration
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public class ProxyAsyncConfiguration extends AbstractAsyncConfiguration { @Bean(name = TaskManagementConfigUtils.ASYNC_ANNOTATION_PROCESSOR_BEAN_NAME)
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public AsyncAnnotationBeanPostProcessor asyncAdvisor() {
Assert.notNull(this.enableAsync, "@EnableAsync annotation metadata was not injected");
AsyncAnnotationBeanPostProcessor bpp = new AsyncAnnotationBeanPostProcessor();
bpp.configure(this.executor, this.exceptionHandler);
Class<? extends Annotation> customAsyncAnnotation = this.enableAsync.getClass("annotation");
if (customAsyncAnnotation != AnnotationUtils.getDefaultValue(EnableAsync.class, "annotation")) {
bpp.setAsyncAnnotationType(customAsyncAnnotation);
}
bpp.setProxyTargetClass(this.enableAsync.getBoolean("proxyTargetClass"));
bpp.setOrder(this.enableAsync.<Integer>getNumber("order"));
return bpp;
} }
ProxyAsyncConfiguration主要是创建了一个基于异步调用的后置处理器（AsyncAnnotationBeanPostProcessor），改BPP中设置了executor（异步线程池）、exceptionHandler（异常处理器）、AsyncAnnotationType（异步注解类型）、proxyTargetClass（代理创建模式）、order（后置处理器执行顺序）。那么executor和exceptionHandler是哪里来的呢、默认值是什么？接着继续向父级探索。
@Configuration
public abstract class AbstractAsyncConfiguration implements ImportAware { ..... /**
* Collect any {@link AsyncConfigurer} beans through autowiring.
*/
@Autowired(required = false)
void setConfigurers(Collection<AsyncConfigurer> configurers) {
if (CollectionUtils.isEmpty(configurers)) {
return;
}
if (configurers.size() > 1) {
throw new IllegalStateException("Only one AsyncConfigurer may exist");
}
AsyncConfigurer configurer = configurers.iterator().next();
this.executor = configurer::getAsyncExecutor;
this.exceptionHandler = configurer::getAsyncUncaughtExceptionHandler;
} }
由此可见，executor和exceptionHandler可以通过AsyncConfigurer自定义配置。需要注意的是，spring容器中只能有一个AsyncConfigurer类型的实例呦。
进入异步实现的正题了，当然是好好研究一下AsyncAnnotationBeanPostProcessor这个后置处理器做了哪些事情了。
public class AsyncAnnotationBeanPostProcessor extends AbstractBeanFactoryAwareAdvisingPostProcessor {
....
@Override
public void setBeanFactory(BeanFactory beanFactory) {
super.setBeanFactory(beanFactory);
AsyncAnnotationAdvisor advisor = new AsyncAnnotationAdvisor(this.executor, this.exceptionHandler);
if (this.asyncAnnotationType != null) {
advisor.setAsyncAnnotationType(this.asyncAnnotationType);
}
advisor.setBeanFactory(beanFactory);
this.advisor = advisor;
}
}
1、添加一个AOP advisor（AsyncAnnotationAdvisor），识别带有@Async注解或者指定类型注解的方法，创建代理类。
2、找一个合适的TaskExecutor来异步调用带有@Async注解或者指定类型注解的方法。
3、如果方法在异步调用过程中抛出异常，将使用合适的ExceptionHandler进行处理。
看到这里，已经有两个疑问了。AsyncAnnotationAdvisor做了什么？如何创建的异步调用代理类？
AsyncAnnotationAdvisor实现原理
大家都知道，Spring Aop中，一个advisor包含一个advice（通知）、pointcut（切点）。
创建advice
protected Advice buildAdvice(
@Nullable Supplier<Executor> executor, @Nullable Supplier<AsyncUncaughtExceptionHandler> exceptionHandler) { AnnotationAsyncExecutionInterceptor interceptor = new AnnotationAsyncExecutionInterceptor(null);
interceptor.configure(executor, exceptionHandler);
return interceptor;
}
AnnotationAsyncExecutionInterceptor是一个方法拦截器，父级接口是我们最熟悉的org.aopalliance.intercept.MethodInterceptor。这个拦截器有个优秀的功能，可以根据不同的方法选择不同的taskexecutor来异步执行，即Async#value()方法的值。
public Object invoke(final MethodInvocation invocation) throws Throwable {
Class<?> targetClass = (invocation.getThis() != null ? AopUtils.getTargetClass(invocation.getThis()) : null);
Method specificMethod = ClassUtils.getMostSpecificMethod(invocation.getMethod(), targetClass);
final Method userDeclaredMethod = BridgeMethodResolver.findBridgedMethod(specificMethod);
AsyncTaskExecutor executor = determineAsyncExecutor(userDeclaredMethod);
if (executor == null) {
throw new IllegalStateException(
"No executor specified and no default executor set on AsyncExecutionInterceptor either");
}
Callable<Object> task = () -> {
try {
Object result = invocation.proceed();
if (result instanceof Future) {
return ((Future<?>) result).get();
}
}
catch (ExecutionException ex) {
handleError(ex.getCause(), userDeclaredMethod, invocation.getArguments());
}
catch (Throwable ex) {
handleError(ex, userDeclaredMethod, invocation.getArguments());
}
return null;
};
return doSubmit(task, executor, invocation.getMethod().getReturnType());
}
拦截器的invoke方法看一下瞬间豁然开朗，寻找方法对应的桥接方法、选择一个合适的异步执行的executor、创建Callback实例（异常的处理）、提交异步调用任务到executor中。
创建pointcut
public interface Pointcut {
/**
* Return the ClassFilter for this pointcut.
* @return the ClassFilter (never {@code null})
*/
ClassFilter getClassFilter();
/**
* Return the MethodMatcher for this pointcut.
* @return the MethodMatcher (never {@code null})
*/
MethodMatcher getMethodMatcher();
/**
* Canonical Pointcut instance that always matches.
*/
Pointcut TRUE = TruePointcut.INSTANCE;
}
public interface Pointcut {
/**
* Return the ClassFilter for this pointcut.
* @return the ClassFilter (never {@code null})
*/
ClassFilter getClassFilter();
/**
* Return the MethodMatcher for this pointcut.
* @return the MethodMatcher (never {@code null})
*/
MethodMatcher getMethodMatcher();
/**
* Canonical Pointcut instance that always matches.
*/
Pointcut TRUE = TruePointcut.INSTANCE;
}
一个切点主要包含两个对象ClassFilter（class过滤器）、MethodMatcher（方法匹配器）。AnnotationMatchingPointcut主要匹配注有@Async或者指定类型注解的class或者方法。
异步代理类调用创建过程
继续回到AsyncAnnotationBeanPostProcessor这个后置处理器，父类AbstractBeanFactoryAwareAdvisingPostProcessor是和AbstractAutoProxyCreator（Spring Aop中最常见的创建Aop Proxy的BPP）同一级别的，主要是曝光代理对象的class、强制设置target-class mode。
@Override
protected ProxyFactory prepareProxyFactory(Object bean, String beanName) {
if (this.beanFactory != null) {
AutoProxyUtils.exposeTargetClass(this.beanFactory, beanName, bean.getClass());
} ProxyFactory proxyFactory = super.prepareProxyFactory(bean, beanName);
if (!proxyFactory.isProxyTargetClass() && this.beanFactory != null &&
AutoProxyUtils.shouldProxyTargetClass(this.beanFactory, beanName)) {
proxyFactory.setProxyTargetClass(true);
}
return proxyFactory;
}
如何判断bean是否需要创建proxy呢？
@Override
protected boolean isEligible(Object bean, String beanName) {
return (!AutoProxyUtils.isOriginalInstance(beanName, bean.getClass()) &&
super.isEligible(bean, beanName));
}
AbstractAdvisingBeanPostProcessor.java
protected boolean isEligible(Class<?> targetClass) {
Boolean eligible = this.eligibleBeans.get(targetClass);
if (eligible != null) {
return eligible;
}
if (this.advisor == null) {
return false;
}
eligible = AopUtils.canApply(this.advisor, targetClass);
this.eligibleBeans.put(targetClass, eligible);
return eligible;
}
AopUtils.java
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;
}
}
首先当前处理的bean是最原始的实例，然后通过advisor的pointcut去判断。
继续追踪父级AbstractAdvisingBeanPostProcessor。
public Object postProcessAfterInitialization(Object bean, String beanName) {
if (this.advisor == null || bean instanceof AopInfrastructureBean) {
// Ignore AOP infrastructure such as scoped proxies.
return bean;
}
if (bean instanceof Advised) {
Advised advised = (Advised) bean;
if (!advised.isFrozen() && isEligible(AopUtils.getTargetClass(bean))) {
// Add our local Advisor to the existing proxy's Advisor chain...
if (this.beforeExistingAdvisors) {
advised.addAdvisor(0, this.advisor);
}
else {
advised.addAdvisor(this.advisor);
}
return bean;
}
}
if (isEligible(bean, beanName)) {
ProxyFactory proxyFactory = prepareProxyFactory(bean, beanName);
if (!proxyFactory.isProxyTargetClass()) {
evaluateProxyInterfaces(bean.getClass(), proxyFactory);
}
proxyFactory.addAdvisor(this.advisor);
customizeProxyFactory(proxyFactory);
return proxyFactory.getProxy(getProxyClassLoader());
}
// No proxy needed.
return bean;
}
这个抽象类中实现了BPP的postProcessAfterInitialization方法。如果bean是Advised，则将AsyncAnnotationAdvisor添加到Advised实例中去；如果是一个可以创建异步调用代理的bean，通过ProxyFactory创建代理对象。
二、正确实现异步调用
1、启动类新增注解@EnableAsync
2、通过AsyncConfigurerSupport创建异步调用线程池，合理设置相关配置参数，如下。
@Configuration
public class MyAsyncConfigurer extends AsyncConfigurerSupport {
private static Logger LOGGER = LoggerFactory.getLogger(MyAsyncConfigurer.class); @Override
public Executor getAsyncExecutor() {
ThreadPoolTaskExecutor taskExecutor = new ThreadPoolTaskExecutor();
taskExecutor.setCorePoolSize(2);
taskExecutor.setMaxPoolSize(4);
taskExecutor.setQueueCapacity(10);
taskExecutor.setRejectedExecutionHandler((runnable, executor) -> LOGGER.error("异步线程池拒绝任务..." + runnable));
taskExecutor.setThreadFactory(new MyAsyncThreadFactory());
taskExecutor.initialize();
return taskExecutor;
} static class MyAsyncThreadFactory implements ThreadFactory {
private static final AtomicInteger poolNumber = new AtomicInteger(1);
private final ThreadGroup group;
private final AtomicInteger threadNumber = new AtomicInteger(1);
private final String namePrefix; MyAsyncThreadFactory() {
SecurityManager s = System.getSecurityManager();
group = (s != null) ? s.getThreadGroup() :
Thread.currentThread().getThreadGroup();
namePrefix = "myasync-pool-" +
poolNumber.getAndIncrement() +
"-thread-";
} @Override
public Thread newThread(Runnable r) {
Thread t = new Thread(group, r,
namePrefix + threadNumber.getAndIncrement(),
0);
if (t.isDaemon())
t.setDaemon(false);
if (t.getPriority() != Thread.NORM_PRIORITY)
t.setPriority(Thread.NORM_PRIORITY);
return t;
}
}
}
3、成员方法异步调用、内部类方法异步调用、spring retry功能整合到异步调用
@Component
public class MyAsyncTask { private static Logger LOGGER = LoggerFactory.getLogger(MyAsyncConfigurer.class); /**
* Lazy 功能
*
* @see DefaultListableBeanFactory#resolveDependency(DependencyDescriptor, String, Set, TypeConverter)
* <p>
* Spring Bean创建-解决依赖 参考链接：https://blog.csdn.net/finalcola/article/details/81537380
*/
@Lazy
@Autowired
private MyInnerAsyncTask myInnerAsyncTask; @Autowired
private AsyncWrapped asyncWrapped; @Async
public void async() {
LOGGER.error("async");
} public void asyncInner() {
myInnerAsyncTask.async();
} public void asyncWrapped() {
asyncWrapped.asyncProcess(() -> LOGGER.error("async wrapped"), null, null);
} public void asyncWrappedWithRetry() {
Retry retry = new Retry(2, 1000);
asyncWrapped.asyncProcess(() -> {
throw new RuntimeException("async wrapped with retry");
}, null, retry);
} public void asyncWrappedWithRetry2() {
try {
asyncWrapped.asyncProcess(() -> {
throw new RuntimeException("async wrapped with retry2");
});
} catch (Exception e) {
LOGGER.error("异步调用异常...", e);
}
} private class MyInnerAsyncTask {
@Async
public void async() {
LOGGER.error("async inner");
}
} @Configuration
public static class MyAsyncTaskConfiguration {
@Bean
public MyInnerAsyncTask myInnerAsyncTask(MyAsyncTask myAsyncTask) {
return myAsyncTask.new MyInnerAsyncTask();
}
}
}
@Component
public class AsyncWrapped {
protected static Logger LOGGER = LoggerFactory.getLogger(AsyncWrapped.class); @Async
public void asyncProcess(Runnable runnable, Callback callback, Retry retry) {
try {
if (retry == null) {
retry = new Retry(1);
}
retry.execute(ctx -> {
runnable.run();
return null;
}, ctx -> {
if (callback != null) {
callback.call();
}
return null;
});
} catch (Exception e) {
LOGGER.error("异步调用异常...", e);
}
} @Async
@Retryable(value = Exception.class, maxAttempts = 3, backoff = @Backoff(delay = 2000, multiplier = 1.5))
public void asyncProcess(Runnable runnable) throws Exception {
System.out.println("重试中...");
runnable.run();
} @FunctionalInterface
public interface Runnable {
void run() throws Exception;
} @FunctionalInterface
public interface Callback {
void call();
}
}
三、Spring Aop拦截器链
本来没有写这块的东西，Spring异步调用整合了Spring Retry功能之后，就像看一下二者是如何协调工作的。
开启异步和重试功能，仅需要加上这两个注解@EnableAsync、@EnableRetry。
大家可以看一下RetryConfiguration这个类，直接告诉大家了，它是一个advisor，直接注册到spring容器当中的。AbstractAutoProxyCreator会拿到这个advisor，对具有@Retryable注解的bean创建代理类。分析流程和AsyncAnnotationAdvisor一致，大家可以按照上面讲过的流程分析一下Spring Retry的底层实现原理，这里就不详细说明了。
如下是AbstractAutowireCapableBeanFactory#applyBeanPostProcessorsAfterInitialization（）方法。
@Override
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;
}
上图中AnnotationAwareAspectJAutoProxyCreator是AbstractAdvisorAutoProxyCreator的实例。也就是说AbstractAdvisorAutoProxyCreator类型的后置处理器优先于AsyncAnnotationBeanPostProcessor类型的后置处理器执行。AbstractAdvisorAutoProxyCreator BPP通过BeanFactoryAdvisorRetrievalHelper从当前的BeanFactory中拿到所有的advisor。
然后针对当前的bean（beanName = asyncWrapped ）筛选出合适的advisor集合（包含RetryConfiguration实例）。最后是通过ProxyFactory创建的代理类，具体如下。
ProxyFactory通过默认AopProxyFactory即DefaultAopProxyFactory来创建Aop Proxy。
到这里，beanName = asyncWrapped 关于Retryable的代理对象已经创建完毕，并返回代理对象替代当前的bean。然后继续到AsyncAnnotationBeanPostProcessor#postProcessAfterInitialization（）方法，处理关于带有@Async注解的bean。
//如果是advised
if (bean instanceof Advised) {
Advised advised = (Advised) bean;
if (!advised.isFrozen() && isEligible(AopUtils.getTargetClass(bean))) {
// Add our local Advisor to the existing proxy's Advisor chain...
if (this.beforeExistingAdvisors) {
advised.addAdvisor(0, this.advisor);
}
else {
advised.addAdvisor(this.advisor);
}
return bean;
}
} //这里的逻辑不会执行了
if (isEligible(bean, beanName)) {
ProxyFactory proxyFactory = prepareProxyFactory(bean, beanName);
if (!proxyFactory.isProxyTargetClass()) {
evaluateProxyInterfaces(bean.getClass(), proxyFactory);
}
proxyFactory.addAdvisor(this.advisor);
customizeProxyFactory(proxyFactory);
return proxyFactory.getProxy(getProxyClassLoader());
}
以前总以为多个注解，就会多次创建代理，一层一层嵌套。现在明白了，是通过拦截器链来完成的。此时beanName = asyncWrapped对应的bean已经是Advised类型的实例了，然后将AsyncAnnotationAdvisor实例添加到Advised实例的advisors集合中。
为啥beanName = asyncWrapped对应的bean是Advised类型的实例？那还要从对beanName = asyncWrapped的bean创建代理类说起。那么接着回到通过DefaultAopProxyFactory来创建Aop Proxy。这里看一下CglibAopProxy，JdkDynamicAopProxy请自行查看。以下代码来自CglibAopProxy#getProxy（）方法。
......
//设置需要代理的接口
enhancer.setInterfaces(AopProxyUtils.completeProxiedInterfaces(this.advised));
......
//获取callbacks
Callback[] callbacks = getCallbacks(rootClass);
......
//设置callback filter
enhancer.setCallbackFilter(new ProxyCallbackFilter(
this.advised.getConfigurationOnlyCopy(), this.fixedInterceptorMap, this.fixedInterceptorOffset));
.....
设置需要代理的接口，除了目标类包含的接口，还需要添加一些额外的接口。如下是AopProxyUtils#completeProxiedInterfaces（）方法中的内容。
......
if (addSpringProxy) {
proxiedInterfaces[index] = SpringProxy.class;
index++;
}
if (addAdvised) {
proxiedInterfaces[index] = Advised.class;
index++;
}
if (addDecoratingProxy) {
proxiedInterfaces[index] = DecoratingProxy.class;
}
......
看到了Advised.class哈，这就是为啥最终的代理对象是Advised类型的实例了。
获取callbacks集合，注意this.advisedDispatcher在数组中的索引是4，下面会用到。
Callback[] mainCallbacks = new Callback[] {
aopInterceptor, // for normal advice
targetInterceptor, // invoke target without considering advice, if optimized
new SerializableNoOp(), // no override for methods mapped to this
targetDispatcher, this.advisedDispatcher,
new EqualsInterceptor(this.advised),
new HashCodeInterceptor(this.advised)
};
设置callback filters，如下是ProxyCallbackFilter#accept(Method method)部分源码。
......
if (!this.advised.isOpaque() && method.getDeclaringClass().isInterface() &&
method.getDeclaringClass().isAssignableFrom(Advised.class)) {
if (logger.isTraceEnabled()) {
logger.trace("Method is declared on Advised interface: " + method);
}
return DISPATCH_ADVISED;
}
......
ProxyCallbackFilter的作用主要是根据不同类型的method，返回callbacks数组的索引。上面的DISPATCH_ADVISED变量的值是4。
这个AdvisedDispatcher是干什么的呢？
//Dispatcher for any methods declared on the Advised class.
private static class AdvisedDispatcher implements Dispatcher, Serializable { private final AdvisedSupport advised; public AdvisedDispatcher(AdvisedSupport advised) {
this.advised = advised;
} @Override
public Object loadObject() throws Exception {
return this.advised;
}
}
也就是如果method是Advised.class声明的，则使用AdvisedDispatcher进行分发。
AsyncAnnotationBeanPostProcessor#postProcessAfterInitialization（） //如果是advised
if (bean instanceof Advised) {
Advised advised = (Advised) bean;
if (!advised.isFrozen() && isEligible(AopUtils.getTargetClass(bean))) {
// Add our local Advisor to the existing proxy's Advisor chain...
if (this.beforeExistingAdvisors) {
advised.addAdvisor(0, this.advisor);
}
else {
advised.addAdvisor(this.advisor);
}
return bean;
}
}
上面的advised.addAdvisor(0, this.advisor); 相当于如下代码。
//spring aop cglib代理对象
public class XXXX$$EnhancerBySpringCGLIB$$8f47b115 implements Advised {
private org.springframework.cglib.proxy.Dispatcher advisedDispatcher;//AdvisedDispatcher实例
...... @Override
public void addAdvisor(int pos, Advisor advisor) throws AopConfigException() {
advisedDispatcher.loadObject().addAdvisor(pos, advisor);
} ......
}
还需要补充的一个地方就是callbacks数组中有个aopInterceptor，对应的类型是DynamicAdvisedInterceptor（General purpose AOP callback. Used when the target is dynamic or when the proxy is not frozen.）。
如上图所示，intercept方法中会通过advised(AdvisedSupport type, The configuration used to configure this proxy.)实例获取一个拦截器链，如果不为空，则返回一个CglibMethodInvocation实例。
简单总结一下获取拦截器链的过程， 如下。
1、从缓存中获取当前方法的拦截器链
2、若缓存未命中，则调用 getInterceptorsAndDynamicInterceptionAdvice 获取拦截器链
3、遍历通知器列表
4、对于 PointcutAdvisor 类型的通知器，这里要调用通知器所持有的切点（Pointcut）对类和方法进行匹配，匹配成功说明应向当前方法织入通知逻辑
5、调用 getInterceptors 方法对非 MethodInterceptor 类型的通知进行转换
6、返回拦截器数组，并在随后存入缓存中
CglibMethodInvocation的父类是ReflectiveMethodInvocation，ReflectiveMethodInvocation 贯穿于拦截器链执行的始终。
public class ReflectiveMethodInvocation implements ProxyMethodInvocation {
private int currentInterceptorIndex = -1;
public Object proceed() throws Throwable {
// 拦截器链中的最后一个拦截器执行完后，即可执行目标方法
if (this.currentInterceptorIndex == this.interceptorsAndDynamicMethodMatchers.size() - 1) {
// 执行目标方法
return invokeJoinpoint();
}
Object interceptorOrInterceptionAdvice =
this.interceptorsAndDynamicMethodMatchers.get(++this.currentInterceptorIndex);
if (interceptorOrInterceptionAdvice instanceof InterceptorAndDynamicMethodMatcher) {
InterceptorAndDynamicMethodMatcher dm =
(InterceptorAndDynamicMethodMatcher) interceptorOrInterceptionAdvice;
/*
* 调用具有三个参数（3-args）的 matches 方法动态匹配目标方法，
* 两个参数（2-args）的 matches 方法用于静态匹配
*/
if (dm.methodMatcher.matches(this.method, this.targetClass, this.arguments)) {
// 调用拦截器逻辑
return dm.interceptor.invoke(this);
}
else {
// 如果匹配失败，则忽略当前的拦截器
return proceed();
}
}
else {
// 调用拦截器逻辑，并传递 ReflectiveMethodInvocation 对象
return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);
}
}
}
所以整个拦截器链的调用流程大约长这样（盗图一张）。
大家在写MethodInterceptor 的时候注意了，一定要调用MethodInvocation 的 proceed（）方法，否则不能执行拦截器链。
public SelfMethodInterceptor implements MethodInterceptor {
public Object invoke(MethodInvocation invocation) throws Throwable {
//前置逻辑
Object ret=invocation.proceed();
//错误的写法，无法执行拦截器链
//Object ret = invocation.getMethod().invoke(invocation.getThis(), invocation.getArguments());
//后置逻辑
return ret;
}
}
四、参考
五、总结
至此，Spring异步调用原理及SpringAop拦截器链都已经分析完毕，希望对大家使用spring异步调用有所帮助。另外我自己也重新温习了spring aop相关的知识，也希望大家对spring aop有一个新的认识。如果有需要源码的同学，请f访问我的github：Spring异步调用原理及实现方案demo。