控制器线程正在等待 Async 方法响应

Question

我是 Spring Boot 新手，想了解更多有关 DeferredResult 和 @Async 方法的信息。我在控制器中创建了一个方法，如下所示，它运行良好。

   @GetMapping("/temp/{id}")
   public DeferredResult<ResponseEntity<?>> findByIdTemp(@PathVariable Long id) throws InterruptedException {

        System.out.println("Request received : "+Thread.currentThread().getName());
        final DeferredResult<ResponseEntity<?>> deferredResult = new DeferredResult<>();
        ForkJoinPool.commonPool().submit(() -> {
            System.out.println("Processing in separate thread");
            try {
                Thread.sleep(6000);
            } catch (InterruptedException e) {
            }
            deferredResult.setResult(ResponseEntity.ok("ok"));
        });

        System.out.println("Thread freed : " +Thread.currentThread().getName());
        return deferredResult;
    }

以下是我收到的输出。

Request received : http-nio-8080-exec-1
Thread freed : http-nio-8080-exec-1
Processing in separate thread

然后我在服务类中创建@Async 方法并在配置类中启用异步。

@Configuration
@EnableAsync
public class ThreadPoolConfiguration {
    @Autowired
    private ExecutorConfiguration configuration;

    @Bean(name = "threadPool")
    public Executor threadPoolTaskExecutor() {
        ThreadPoolTaskExecutor threadPool = new ThreadPoolTaskExecutor();
        threadPool.setCorePoolSize(configuration.getDnCallBackPoolSize());
        return threadPool;
    }
}

    @Async("threadPool")
    public Future<String> getResult() throws InterruptedException {
        System.out.println("Separate thread : "+Thread.currentThread().getName());
        Thread.sleep(6000);
        return new AsyncResult<>("Success");
    }

然后我从控制器类中调用了服务方法

    @GetMapping("/temp/{id}")
    public DeferredResult<ResponseEntity<?>> findByIdTemp(@PathVariable Long id) {

        System.out.println("Request received : "+Thread.currentThread().getName());
        final DeferredResult<ResponseEntity<?>> deferredResult = new DeferredResult<>();
        ResponseDTO responseDTO = null;
        try {
            responseDTO = ResponseDTO.builder()
                    .status(HttpStatus.OK.toString())
                    .body(productService.getResult().get()).build();

            ResponseEntity responseEntity = ResponseEntity.ok(responseDTO);
            deferredResult.setResult(responseEntity);
        } catch (InterruptedException e) {
            System.out.println(e.getMessage());
        } catch (ExecutionException e) {
            System.out.println(e.getMessage());
        }
        System.out.println("Thread freed : " +Thread.currentThread().getName());
        return deferredResult;
    }

但我得到的结果不一样

Request received : http-nio-8080-exec-1
Separate thread : dnCallBackPool-1
Thread freed : http-nio-8080-exec-1

控制器方法似乎正在等待服务方法的响应。谁能告诉我如何正确使用 DeferredResult 和 @Async 方法。

Answer 1

控制器方法似乎正在等待服务方法的响应。

是的，控制器方法正在等待来自productService的响应，因为来自dnCallBackPool的@Async线程只负责执行productService中的getResult()方法。

但是try-catch块中的代码是由Web容器线程执行的（例如http-nio-8080-exec-1）

responseDTO = ResponseDTO.builder()
                .status(HttpStatus.OK.toString())
                .body(productService.getResult()**.get()**).build();

所以Future对象get()调用productService.getResult()是一个阻塞调用，当前线程应该等到@Async线程完成它的过程并返回结果

如有必要，等待计算完成，然后检索其结果。

在控制器方法末尾的Future对象上的get()也是如此，以便两个方法并行执行，下面是一个示例

控制器：

 @GetMapping("/temp/{id}")
public DeferredResult<ResponseEntity<?>> findByIdTemp(@PathVariable Long id) {

    System.out.println("Request received : "+Thread.currentThread().getName());
    final DeferredResult<ResponseEntity<?>> deferredResult = new DeferredResult<>();

    Future<String> future = productService.getResult();   //Async call to service method
    System.out.println("Current Thread Execution: " +Thread.currentThread().getName());    // Execute parallely and print this line immediately 

    ResponseDTO responseDTO = null;
    try {
        responseDTO = ResponseDTO.builder()
                .status(HttpStatus.OK.toString())
                .body(future.get()).build();   // current thread waits for result

         System.out.println("Thread freed : " +Thread.currentThread().getName());    // This line prints as soon as service tasks completes
        ResponseEntity responseEntity = ResponseEntity.ok(responseDTO);
        deferredResult.setResult(responseEntity);
    } catch (InterruptedException e) {
        System.out.println(e.getMessage());
    } catch (ExecutionException e) {
        System.out.println(e.getMessage());
    }

    return deferredResult;

服务：

  @Async("threadPool")
public Future<String> getResult() throws InterruptedException {
    System.out.println("Separate thread : "+Thread.currentThread().getName());
    Thread.sleep(6000);
    System.out.println("Separate thread Async task completed : "+Thread.currentThread().getName());
    return new AsyncResult<>("Success");
}