Spring 异步请求

背景

web请求的时候，有时候会遇到后台操作耗时特别久的操作，前端UI界面总是会请求超时。

举例

代码

@Service
public class AsyncTaskService {
    private Logger logger = LoggerFactory.getLogger(AsyncTaskService.class);
    public String uuid(){
        try{
            TimeUnit.MILLISECONDS.sleep(5000);
            logger.info("working thread");
        } catch (InterruptedException e) {
            logger.error("uuid error ", e);
        }
        return UUID.randomUUID().toString();
    }
}

@RestController
public class AsyncController {
    @Autowired
    AsyncTaskService asyncTaskService;
    @GetMapping("blockingrequest")
    public String blockingRequest() {
        logger.info("blockingRequest: start");
        String uuid = asyncTaskService.uuid();
        logger.info("blockingRequest: end");
        return uuid;
    }
}

结果：

5s后返回response。

目标

开一个子线程异步执行耗时任务。

解决方案

1. @Async

public class AsyncTaskService {
    @Async
    public String getUuid() {
        try {
            TimeUnit.MILLISECONDS.sleep(5000);
            logger.info("working thread");
        } catch (InterruptedException e) {
            logger.error("getUuid error ", e);
        }
        return UUID.randomUUID().toString();
    }
}

@RestController
public class AsyncController {
    @Autowired
    AsyncTaskService asyncTaskService;
    @GetMapping("asyncMethod")
    public String asyncMethod() {
        logger.info("asyncMethod: start");
        String uuid = asyncTaskService.getUuid();
        logger.info("asyncMethod: end");
        return uuid;
    }
}

5s后返回response。

好像没什么用，待查。

2. Callable

@RestController
public class AsyncController {
    @Autowired
    AsyncTaskService asyncTaskService;
    @GetMapping("callable")
    public Callable<String> callable() {
        logger.info("callable: start");
        Callable<String> callable = () -> {
            String uuid = asyncTaskService.uuid();
            logger.info("child task thread");
            return uuid;
        };
        logger.info("callable: end");
        return callable;
    }
}

5s后返回response。虽然先打印了”callable: end”，但是还是会等到线程返回结果后，再返回给UI。还是会超时。

3. DefferedResult

@RestController
public class AsyncController {
    @Autowired
    AsyncTaskService asyncTaskService;
    @GetMapping("deferredResultRequest")
    public DeferredResult<String> deferredResultRequest() {
        logger.info("deferredResultRequest: start");
        DeferredResult<String> deferredResult = new DeferredResult<>(2000l);
        //可使用线程池
//        ExecutorService executorService = Executors.newFixedThreadPool(10);
//        executorService.submit(() -> {
//            asyncTaskService.uuid(request, response);
//            deferredResult.setResult("watch:complete");
//        });
        new Thread(()-> {
            asyncTaskService.uuid();
            deferredResult.setResult("deferredResultRequest:complete");
        }).start();
        deferredResult.onTimeout(() -> deferredResult.setResult("deferredResultRequest:timeout"));
        deferredResult.onCompletion(()->deferredResult.setResult("deferredResultRequest:complete"));
        deferredResult.onError(throwable -> deferredResult.setErrorResult("deferredResultRequest:error"));
        logger.info("deferredResultRequest: return");
        return deferredResult;
    }
}

返回结果：deferredResultRequest:timeout
可在设置的时间内返回结果给UI，不论子线程是否完成。