springboot 长轮询实现

超、凢脫俗 2022-03-17 06:50 428阅读 0赞

### springboot 长轮询实现 ###

> 基于 @EnableAsync , @Sync

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

@RequestMapping("/async")
    @RestController
    public class AsyncRequestDemo {
    
        @Autowired
        private AsyncRequestService asyncRequestService;
    
        @GetMapping("/value")
        public String getValue() {
    
            String msg =  null;
            Future<String> result = null;
            try{
                result = asyncRequestService.getValue();
                msg = result.get(10, TimeUnit.SECONDS);
            }catch (Exception e){
                e.printStackTrace();
            }finally {
                if (result != null){
                    result.cancel(true);
                }
            }
    
            return msg;
        }
    
        @PostMapping("/value")
        public void postValue(String msg) {
            asyncRequestService.postValue(msg);
        }
    }

@Service
    public class AsyncRequestService {
    
        private String msg = null;
    
        @Async
        public Future<String> getValue() throws InterruptedException {
    
            while (true){
                synchronized (this){
                    if (msg != null){
                        String resultMsg = msg;
                        msg = null;
                        return new AsyncResult(resultMsg);
                    }
                }
                Thread.sleep(100);
            }
        }
    
        public synchronized void postValue(String msg) {
            this.msg = msg;
        }
    }

#### 备注 ####

1.  `@EnableAsync` 开启异步
2.  `@Sync` 标记异步方法
3.  `Future` 用于接收异步返回值
4.  `result.get(10, TimeUnit.SECONDS);` 阻塞，超时获取结果
5.  `Future.cancel()` 中断线程