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前提背景
开启异步任务使用方法:
-
方法上加@Async注解
-
启动类或者配置类上@EnableAsync
@EnableAsync
源码注释
Enables Spring's asynchronous method execution capability, similar to functionality found in Spring's task:* XML namespace.
To be used together with @Configuration classes as follows, enabling annotation-driven async processing for an entire Spring application context:
- @EnableAsync主要的目的就是开启spring异步执行器,有点类似之前xml中的task标签配置,需要联合@Configuration注解一起使用。
使用模式
@Configuration
@EnableAsync
public class AppConfig {}
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MyAsyncBean is a user-defined type with one or more methods annotated with either Spring's @Async annotation, the EJB 3.1 @javax.ejb.Asynchronous annotation, or any custom annotation specified via the annotation() attribute. The aspect is added transparently for any registered bean, for instance via this configuration:
- NyAsyncBean 是用户自己定义的一个或者多个通过@Async注解进行修饰的对象、或者EJB 3.1 @javax.ejb.Asynchronous注解,或者用户自定义的指定的注解操作属性,被注册到切面的功能方法。
@Configuration
public class AnotherAppConfig {
@Bean
public MyAsyncBean asyncBean() {
return new MyAsyncBean();
}
}
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By default, Spring will be searching for an associated thread pool definition: either a unique TaskExecutor bean in the context, or an Executor bean named "taskExecutor" otherwise. If neither of the two is resolvable, a SimpleAsyncTaskExecutor will be used to process async method invocations. Besides, annotated methods having a void return type cannot transmit any exception back to the caller. By default, such uncaught exceptions are only logged.
- 默认情况下spring会先搜索TaskExecutor类型的bean或者名字为taskExecutor的Executor类型的bean,都不存在使用SimpleAsyncTaskExecutor执行器
To customize all this, implement AsyncConfigurer and provide:
your own Executor through the getAsyncExecutor() method, and your own AsyncUncaughtExceptionHandler through the getAsyncUncaughtExceptionHandler() method.
覆盖定制化UncaughtExceptionHandler/getAsyncExecutor
- 可实现AsyncConfigurer接口重写getAsyncExecutor获取异步执行器,getAsyncUncaughtExceptionHandler获取异步未捕获异常处理器
@Configuration
@EnableAsync
public class AppConfig implements AsyncConfigurer {
@Override
public Executor getAsyncExecutor() {
ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
executor.setCorePoolSize(7);
executor.setMaxPoolSize(42);
executor.setQueueCapacity(11);
executor.setThreadNamePrefix("MyExecutor-");
executor.initialize();
return executor;
}
@Override
public AsyncUncaughtExceptionHandler getAsyncUncaughtExceptionHandler() {
return MyAsyncUncaughtExceptionHandler();
}
}
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If only one item needs to be customized, null can be returned to keep the default settings. Consider also extending from AsyncConfigurerSupport when possible.
Note: In the above example the ThreadPoolTaskExecutor is not a fully managed Spring bean. Add the @Bean annotation to the getAsyncExecutor() method if you want a fully managed bean. In such circumstances it is no longer necessary to manually call the executor.initialize() method as this will be invoked automatically when the bean is initialized.
同比相关
<beans>
<task:annotation-driven executor="myExecutor" exception-handler="exceptionHandler"/>
<task:executor id="myExecutor" pool-size="7-42" queue-capacity="11"/>
<bean id="asyncBean" class="com.foo.MyAsyncBean"/>
<bean id="exceptionHandler" class="com.foo.MyAsyncUncaughtExceptionHandler"/>
</beans>
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重点说明
The mode() attribute controls how advice is applied: If the mode is AdviceMode.PROXY (the default), then the other attributes control the behavior of the proxying. 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.
- 这里就说明了@Async必须在不同方法中调用。
Note that if the mode() is set to AdviceMode.ASPECTJ, then the value of the proxyTargetClass() attribute will be ignored. Note also that in this case the spring-aspects module JAR must be present on the classpath, with compile-time weaving or load-time weaving applying the aspect to the affected classes. There is no proxy involved in such a scenario; local calls will be intercepted as well.//当然也可以用Aspect模式织入(需要引入spring-aspects模块需要的jar)
功能解析
@Async
-
该注解可以标记一个异步执行的方法,也可以用来标注类,表示类中的所有方法都是异步执行的。
-
入参随意,但返回值只能是void或者Future.(ListenableFuture接口/CompletableFuture类)
-
Future是代理返回的切实的异步返回,用以追踪异步方法的返回值。当然也可以使用AsyncResult类(实现ListenableFuture接口)(Spring或者EJB都有)或者CompletableFuture类
-
加在类上表示整个类都使用,加在方法上会覆盖类上的设置
-
value字段用以限定执行方法的执行器名称(自定义):Executor或者TaskExecutor
@EnableAsync
-
开启spring异步执行器,类似xml中的task标签配置,需要联合@Configuration注解一起使用
-
默认情况下spring会先搜索TaskExecutor类型的bean或者名字为taskExecutor的Executor类型的bean,都不存在使用SimpleAsyncTaskExecutor执行器
-
针对于上面章节的【覆盖定制化UncaughtExceptionHandler/getAsyncExecutor】可实现AsyncConfigurer接口复写getAsyncExecutor获取异步执行器,getAsyncUncaughtExceptionHandler获取异步未捕获异常处理器
-
@Configuration
-
注解类和xml基本一致,但是使用注解类还可以自定义线程名前缀(上面的AppConfig-》getAsyncExecutor-》setThreadNamePrefix)
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(AsyncConfigurationSelector.class)
public @interface EnableAsync {
/**该属性用来支持用户自定义异步注解,默认扫描spring的@Async和EJB3.1的@code @javax.ejb.Asynchronous
* 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;
/**标明是否需要创建CGLIB子类代理,AdviceMode=PROXY时才适用。注意设置为true时,其它spring管理的bean也会升级到CGLIB子类代理
* 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;
/**标明异步通知将会如何实现,默认PROXY,如需支持同一个类中非异步方法调用另一个异步方法,需要设置为ASPECTJ
* 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;
/**标明异步注解bean处理器应该遵循的执行顺序,默认最低的优先级(Integer.MAX_VALUE,值越小优先级越高)
* 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;
}
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执行流程
核心注解就是@Import(AsyncConfigurationSelector.class),就是属于ImportSelector接口的selectImports()方法,源码如下:
查询器:基于@EnableAsync中定义的模式AdviceMode加在@Configuration标记的类上,确定抽象异步配置类的实现类
/**
* Selects which implementation of {@link AbstractAsyncConfiguration} should be used based
* on the value of {@link EnableAsync#mode} on the importing {@code @Configuration} class.
*
* @author Chris Beams
* @since 3.1
* @see EnableAsync
* @see ProxyAsyncConfiguration
*/
public class AsyncConfigurationSelector extends AdviceModeImportSelector<EnableAsync> {
private static final String ASYNC_EXECUTION_ASPECT_CONFIGURATION_CLASS_NAME =
"org.springframework.scheduling.aspectj.AspectJAsyncConfiguration";
/**
* {@inheritDoc}
* @return {@link ProxyAsyncConfiguration} or {@code AspectJAsyncConfiguration} for
* {@code PROXY} and {@code ASPECTJ} values of {@link EnableAsync#mode()}, respectively
*/
@Override
public String[] selectImports(AdviceMode adviceMode) {
switch (adviceMode) {
case PROXY://如果配置的PROXY,使用ProxyAsyncConfiguration
return new String[] { ProxyAsyncConfiguration.class.getName() };
case ASPECTJ://如果配置的ASPECTJ,使用ProxyAsyncConfiguration
return new String[] { ASYNC_EXECUTION_ASPECT_CONFIGURATION_CLASS_NAME };
default:
return null;
}
}
}
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JDK接口代理-选一个类ProxyAsyncConfiguration:
@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();
Class<? extends Annotation> customAsyncAnnotation = this.enableAsync.getClass("annotation");
if (customAsyncAnnotation != AnnotationUtils.getDefaultValue(EnableAsync.class, "annotation")) {
bpp.setAsyncAnnotationType(customAsyncAnnotation);
}
if (this.executor != null) {
bpp.setExecutor(this.executor);
}
if (this.exceptionHandler != null) {
bpp.setExceptionHandler(this.exceptionHandler);
}
bpp.setProxyTargetClass(this.enableAsync.getBoolean("proxyTargetClass"));
bpp.setOrder(this.enableAsync.<Integer>getNumber("order"));
return bpp;
}
}
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-
如果@EnableAsync中用户自定义了annotation属性,即异步注解类型
-
新建一个异步注解bean后处理器
-
设置Executor:设置线程任务执行器
-
AsyncUncaughtExceptionHandler:设置异常处理器
-
设置是否升级到CGLIB子类代理,默认不开启
-
设置执行优先级,默认最后执行
ProxyAsyncConfiguration就两点:
-
就是继承了AbstractAsyncConfiguration类
-
定义了一个bean:AsyncAnnotationBeanPostProcessor
AbstractAsyncConfiguration
/**
* Abstract base {@code Configuration} class providing common structure for enabling
* Spring's asynchronous method execution capability.
* 抽象异步配置类,封装了通用结构,用以支持spring的异步方法执行能力
* @author Chris Beams
* @author Stephane Nicoll
* @since 3.1
* @see EnableAsync
*/
@Configuration
public abstract class AbstractAsyncConfiguration implements ImportAware {
protected AnnotationAttributes enableAsync;//enableAsync的注解属性
protected Executor executor;//Doug Lea老李头设计的线程任务执行器
protected AsyncUncaughtExceptionHandler exceptionHandler;//异常处理器
@Override
public void setImportMetadata(AnnotationMetadata importMetadata) {
this.enableAsync = AnnotationAttributes.fromMap(
importMetadata.getAnnotationAttributes(EnableAsync.class.getName(), false));
if (this.enableAsync == null) {
throw new IllegalArgumentException(
"@EnableAsync is not present on importing class " + importMetadata.getClassName());
}
}
/**
* 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();
}
}
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主要设置为一下三点
- 1)注解属性
- 2)异步任务执行器
- 3)异常处理器
方法:
- 1)setImportMetadata 设置注解属性
- 2)setConfigurers 设置异步任务执行器和异常处理器
AsyncAnnotationBeanPostProcessor
AsyncAnnotationBeanPostProcessor这个类的Bean 初始化时 : BeanFactoryAware接口setBeanFactory方法中,对AsyncAnnotationAdvisor异步注解切面进行了构造。
@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;
}
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AsyncAnnotationAdvisor:
通过AsyncAnnotationAdvisor建立异步化的AOP切面拦截操作处理机制
-
AsyncAnnotationBeanPostProcessor -> postProcessAfterInitialization()
-
具体的后置处理:AsyncAnnotationBeanPostProcessor的后置bean处理是通过其父类AbstractAdvisingBeanPostProcessor来实现的,
-
该类实现了BeanPostProcessor接口,复写postProcessAfterInitialization方法
@Override
public Object postProcessAfterInitialization(Object bean, String beanName) {
if (bean instanceof AopInfrastructureBean) {
// Ignore AOP infrastructure such as scoped proxies.
return bean;
}
//把Advisor添加进bean ProxyFactory-》AdvisedSupport-》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;
}
}
//构造ProxyFactory代理工厂,添加代理的接口,设置切面,最后返回代理类:AopProxy
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 async proxy needed.
return bean;
}
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-
isEligible用于判断这个类或者这个类中的某个方法是否含有注解,AsyncAnnotationAdvisor 实现了PointcutAdvisor接口。
-
代理AopProxy接口,我们这里最终实际生成的是JdkDynamicAopProxy
// 得到方法的拦截器链
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 {
// 构造
invocation = new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain);
// Proceed to the joinpoint through the interceptor chain.
retVal = invocation.proceed();
}
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-
@Async注解的拦截器是AsyncExecutionInterceptor,它继承了MethodInterceptor接口。而MethodInterceptor就是AOP规范中的Advice(切点的处理器)。
-
chain不为空,执行第二个分支,构造ReflectiveMethodInvocation,然后执行proceed方法。
@Override
public Object proceed() throws Throwable {
// 如果没有拦截器,直接执行被代理的方法
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;
if (dm.methodMatcher.matches(this.method, this.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.
return ((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);
}
}
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核心方法是InterceptorAndDynamicMethodMatcher.interceptor.invoke(this),实际就是执行了AsyncExecutionInterceptor.invoke。
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(//如果没有自定义异步任务执行器,报下面这行错,不用管,可以默认执行
"No executor specified and no default executor set on AsyncExecutionInterceptor either");
}
Callable<Object> task = new Callable<Object>() {
@Override
public Object call() throws Exception {
try {
Object result = invocation.proceed();
if (result instanceof Future) {
return ((Future<?>) result).get();//阻塞等待执行完毕得到结果
}
}
catch (ExecutionException ex) {
handleError(ex.getCause(), userDeclaredMethod, invocation.getArguments());
}
catch (Throwable ex) {
handleError(ex, userDeclaredMethod, invocation.getArguments());
}
return null;
}
};
//提交有任务给执行器
return doSubmit(task, executor, invocation.getMethod().getReturnType());
}
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执行核心方法doSubmit
protected Object doSubmit(Callable<Object> task, AsyncTaskExecutor executor, Class<?> returnType) {
if (completableFuturePresent) {//先判断是否存在CompletableFuture这个类,优先使用CompletableFuture执行任务
Future<Object> result = CompletableFutureDelegate.processCompletableFuture(returnType, task, executor);
if (result != null) {
return result;
}
}//返回值是可监听Future,定义过回调函数:addCallback
if (ListenableFuture.class.isAssignableFrom(returnType)) {
return ((AsyncListenableTaskExecutor) executor).submitListenable(task);
}//返回值是Future
else if (Future.class.isAssignableFrom(returnType)) {
return executor.submit(task);
}
else {//没有返回值
executor.submit(task);
return null;
}
}
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总体流程
-
从注解开始:@EnableAsync -> ProxyAsyncConfiguration类构造一个bean(类型:AsyncAnnotationBeanPostProcessor)
-
从AsyncAnnotationBeanPostProcessor这个类的bean的生命周期走:AOP-Advisor切面初始化(setBeanFactory())-> AOP-生成代理类AopProxy(postProcessAfterInitialization())-> AOP-切点执行(InvocationHandler.invoke)
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