Callable和DeferredResult

淩亂°似流年 2022-05-23 01:23 184阅读 0赞

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DeferredResult和Callable都是为了异步生成返回值提供基本的支持。简单来说就是一个请求进来，如果你使用了DeferredResult或者Callable，在没有得到返回数据之前，DispatcherServlet和所有Filter就会退出Servlet容器线程，但响应保持打开状态，一旦返回数据有了，这个DispatcherServlet就会被再次调用并且处理，以异步产生的方式，向请求端返回值。

这么做的好处就是请求不会长时间占用服务连接池，提高服务器的吞吐量。

**Callable主要用来处理一些简单的逻辑，DeferredResult主要用于处理一些复杂逻辑。**

#### 一、Callable     ####

call（）方法的返回值就是服务端返回给请求端的数据

@GetMapping("/callable")
        public Callable<String> testCallable() throws InterruptedException {
            log.info("主线程开始！");
            Callable<String> result = new Callable<String>() {
    
                @Override
                public String call() throws Exception {
                    log.info("副线程开始！");
                    Thread.sleep(1000);
                    log.info("副线程结束！");
                    return "SUCCESS";
                }
    
            };
            log.info("主线程结束！");
            return result;
        }

结果：主线程开始   主线程结束    副线程开始  副线程结束

二、DeferredResult

一旦启用了异步请求处理功能 ，控制器就可以将返回值包装在DeferredResult，控制器可以从不同的线程异步产生返回值。优点就是可以实现两个完全不相干的线程间的通信。

一共起来3个线程  主线程  监听线程 和处理任务的线程

1.controller

@RestController
    public class AsyncController {
    	
    	@Autowired
    	private MockQueue mockQueue;
    	
    	@Autowired
    	private DeferredResultHolder deferredResultHolder;
    	
    	private Logger logger = LoggerFactory.getLogger(getClass());
    	
    	@RequestMapping("/order")
    	public DeferredResult<String> order() throws Exception {
    		logger.info("主线程开始");
    		
    		String orderNumber = RandomStringUtils.randomNumeric(8);
    		mockQueue.setPlaceOrder(orderNumber);
    		
    		DeferredResult<String> result = new DeferredResult<>();
    		deferredResultHolder.getMap().put(orderNumber, result);
    		
    		return result;
           }
    }

2.存储DeferredResult的实例

@Component
    public class DeferredResultHolder {
    	
    	private Map<String, DeferredResult<String>> map = new HashMap<String, DeferredResult<String>>();
    
    	public Map<String, DeferredResult<String>> getMap() {
    		return map;
    	}
    
    	public void setMap(Map<String, DeferredResult<String>> map) {
    		this.map = map;
    	}
    	
    }

3.写监听器，作用是产生另一个不相干的线程来给DeferredResult设置返回值

@Component
    public class QueueListener implements ApplicationListener<ContextRefreshedEvent> {
    
    	@Autowired
    	private MockQueue mockQueue;
    
    	@Autowired
    	private DeferredResultHolder deferredResultHolder;
    	
    	private Logger logger = LoggerFactory.getLogger(getClass());
    
    	@Override
    	public void onApplicationEvent(ContextRefreshedEvent event) {
    		new Thread(() -> {
    			while (true) {
    
    				if (StringUtils.isNotBlank(mockQueue.getCompleteOrder())) {
    					
    					String orderNumber = mockQueue.getCompleteOrder();
    					logger.info("返回订单处理结果:"+orderNumber);
    					deferredResultHolder.getMap().get(orderNumber).setResult("place order success");
    					mockQueue.setCompleteOrder(null);
    					
    				}else{
    					try {
    						Thread.sleep(100);
    					} catch (InterruptedException e) {
    						e.printStackTrace();
    					}
    				}
    
    			}
    		}).start();
    	}
    }

4、Mock数据

@Component
    public class MockQueue {
    
    	private String placeOrder;
    
    	private String completeOrder;
    	
    	private Logger logger = LoggerFactory.getLogger(getClass());
    
    	public String getPlaceOrder() {
    		return placeOrder;
    	}
    
    	public void setPlaceOrder(String placeOrder) throws Exception {
    		new Thread(() -> {
    			logger.info("接到下单请求, " + placeOrder);
    			try {
    				Thread.sleep(1000);
    			} catch (Exception e) {
    				e.printStackTrace();
    			}
    			this.completeOrder = placeOrder;
    			logger.info("下单请求处理完毕," + placeOrder);
    		}).start();
    	}
    
    	public String getCompleteOrder() {
    		return completeOrder;
    	}
    
    	public void setCompleteOrder(String completeOrder) {
    		this.completeOrder = completeOrder;
    	}
    
    }

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[70]: /images/20220523/08471af4f8d34293a5251c3332ca2eeb.png
[70 1]: /images/20220523/c4c1c82957284d738f80a7228e1c0473.png