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@Async 异步注解使用

news 来源：原创 2024/9/12 21:57:45

@Async 异步注解使用

使用版本SpringBoot-2.7.18

使用@EnableAsync开启异步注解

@EnableAsync
@SpringBootApplication
public class TestApplication {public static void main(String[] args) {SpringApplication.run(TestApplication.class, args);}}

在需要的方法上加上@Async

@Service
public class TestServiceImpl implements TestService {@Override@Asyncpublic LocalDateTime async() {return LocalDateTime.now();}
}

Spring Boot使用的异步任务执行器

默认情况异步任务执行器使用ThreadPoolTaskExecutor

在 org.springframework.aop.interceptor.AsyncExecutionInterceptor.invoke() 方法中打断点可以看到使用的是哪个线程池

@Override
@Nullable
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);//1、这里打个断点可以看到使用的是哪个线程池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());
}

直接配置一个异步任务执行器，使用@Async注解，异步任务执行器会更改成 myTaskExecutorA

@Configuration
public class BeanConfigure {@BeanTaskExecutor myTaskExecutorA() {return new MyTaskExecutorA();}public static class MyTaskExecutorA implements TaskExecutor {@Overridepublic void execute(Runnable task) {System.err.println("==========》" + task.getClass());}}
}

恰巧我们配置了两个异步任务执行器，会切换使用 org.springframework.core.task.SimpleAsyncTaskExecutor

@Configuration
public class BeanConfigure {@BeanTaskExecutor myTaskExecutorA() {return new MyTaskExecutorA();}@BeanTaskExecutor myTaskExecutorB() {return new MyTaskExecutorB();}public static class MyTaskExecutorA implements TaskExecutor {@Overridepublic void execute(Runnable task) {System.err.println("==========》" + task.getClass());}}public static class MyTaskExecutorB implements TaskExecutor {@Overridepublic void execute(Runnable task) {System.err.println("==========》" + task.getClass());}}
}

首先， org.springframework.core.task.SimpleAsyncTaskExecutor执行效果不是很好；其次，项目中的其他业务可能会配置使用多于两个的TaskExecutor，所以使用@Async的最佳实践是为其明确指定异步任务执行器：@Async(“myTaskExecutorA”)

@Service
public class TestServiceImpl implements TestService {@Override@Async("myTaskExecutorA")//明确指定需要使用的异步执行器public LocalDateTime async() {return LocalDateTime.now();}
}