Shulou(Shulou.com)06/03 Report--

This article introduces the relevant knowledge of "what is the @ Async principle of Java Spring". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

Catalogue

Preface

How to use @ Async

Second, source code interpretation

How to use @ Async

There are two main steps to using @ Async annotations:

1. Add @ EnableAsync annotation to the configuration class

@ ComponentScan (value = "com.wang") @ Configuration@EnableAsyncpublic class AppConfig {}

two。 Add @ Async to the method that you want to execute asynchronously

@ Servicepublic class CycleService2 {@ Autowired private CycleService1 cycleService1; @ Async public void alsoDo () {System.out.println ("create cycleService2");} II. Source code interpretation

The role of 1.@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. *

By default, both Spring's @ {@ link Async} annotation and the EJB 3.1 * {@ code @ javax.ejb.Asynchronous} annotation will be detected. *

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. * what is explained here is that the method execution becomes asynchronous. Which annotation is scanned? currently, the default is Async and Asynchronous. Developers can also customize * / Class targetClass = (invocation.getThis ()! = null)? AopUtils.getTargetClass (invocation.getThis ()): null); Method specificMethod = ClassUtils.getMostSpecificMethod (invocation.getMethod (), targetClass); final Method userDeclaredMethod = BridgeMethodResolver.findBridgedMethod (specificMethod); / * get a task executor * 1. Get the configured task executor * 2 from the @ Async annotation. Find the bean * 3 of the TaskExecutor class from the Spring container. Get the bean named "taskExecutor" from the spring container, * 4. If not, new SimpleAsyncTaskExecutor () * / AsyncTaskExecutor executor = determineAsyncExecutor (userDeclaredMethod); if (executor = = null) {throw new IllegalStateException ("No executor specified and no default executor set on AsyncExecutionInterceptor either") } / / encapsulate the execution of the current method into a callable object, and put it into the thread pool Callable 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 ());}

You can see that the main things to do are:

Find the task executor:

Get the configured task executor from the @ Async annotation

Find the bean of the TaskExecutor class from the Spring container

Get the bean named "taskExecutor" from the spring container

If not, new SimpleAsyncTaskExecutor () can see that we can actually configure the task executor for @ Async.

Encapsulate the specific method into an object of callable, and then doSubmit

Here we'll take a look at the default doSumit, how the SimpleAsyncTaskExecutor is implemented.

The following doExecute method will eventually be executed, and by default threadFactory is null, so by default, our method is created a new daemon thread each time to execute the method.

Protected void doExecute (Runnable task) {Thread thread = (this.threadFactory! = null? This.threadFactory.newThread (task): createThread (task); thread.start ();}

3.3.1.2 Custom Task Actuator

You can new SimpleAsyncTaskExecutor () and then setThreadFactory in the configuration class, which modifies the way the default thread is generated

A more mainstream way is to define a ThreadPoolTaskExecutor, that is, a thread pool task executor, which can be used for thread reuse.

3.3.2 buildPointcut

/ * Calculate a pointcut for the given async annotation types, if any. * @ param asyncAnnotationTypes the async annotation types to introspect * @ return the applicable Pointcut object, or {@ code null} if none * / protected Pointcut buildPointcut (Set

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