Spring Boot實戰|異步調用

《JavaEE開發的顛覆者: Spring Boot實戰》系列讀書筆記

Spring boot異步調用@Async

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什麼是異步調用？

• 異步調用是相對於同步調用而言的，同步調用是指程序按預定順序一步步執行，每一步必須等到上一步執行完後才能執行，異步調用則無需等待上一步程序執行完即可執行。

如何實現異步調用？

• 多線程是一種實現異步調用的方式，在非spring目項目中我們要實現異步調用的就是使用多線程方式，可以自己實現Runable接口或者集成Thread類，或者使用Executors線程池。

  SpringBoot中則提供了很方便的方式執行異步調用，一個@Async就可搞定。

開始使用

• 在啓動類上加上@EnableAsync註解開啓異步

controller層

• 寫一個同步接口和異步接口，在需要異步的執行方法上添加@Async註解

  @RequestMapping("async")
  @RestController
  public class AsyncTaskController {
  	
  	@Autowired
  	private AsyncTask asyncTask;
  
  	@RequestMapping(value = "doTask",method = RequestMethod.GET)
  	public String doTask() throws InterruptedException{
  		long currentTimeMillis = System.currentTimeMillis();
  		asyncTask.task1();
  		asyncTask.task2();
  		asyncTask.task3();
  		long currentTimeMillis1 = System.currentTimeMillis();
  		System.out.println("異步任務總耗時:"+(currentTimeMillis1-currentTimeMillis)+"ms");
  		return "success";
  		
  	}
  	@RequestMapping("justDo")
  	public String justDo() throws InterruptedException{
  		long currentTimeMillis = System.currentTimeMillis();
  		task1();
  		task2();
  		task3();
  		long currentTimeMillis1 = System.currentTimeMillis();
  		System.out.println("任務總耗時:"+(currentTimeMillis1-currentTimeMillis)+"ms");
  		return "success";
  
  	}
  
  	@RequestMapping("doTaskSuccess")
  	public String doTaskSuccess() throws InterruptedException{
  		long currentTimeMillis = System.currentTimeMillis();
  		Future<String> task1 = asyncTask.task1s();
  		Future<String> task2 = asyncTask.task2s();
  		Future<String> task3 = asyncTask.task3s();
  		String result = null;
  		for (;;) {
  			if(task1.isDone() && task2.isDone() && task3.isDone()) {
  				// 三個任務都調用完成，退出循環等待
  				break;
  			}
  			//Thread.sleep(1000);
  		}
  		long currentTimeMillis1 = System.currentTimeMillis();
  		System.out.println("異步任務總耗時:"+(currentTimeMillis1-currentTimeMillis)+"ms");
  		return "success";
  	}
  
  	public String threadAsynchSayHello() {
  		Runnable runnable = ()-> {
  			try {
  				long currentTimeMillis = System.currentTimeMillis();
  				Thread.sleep(1000);
  				long currentTimeMillis1 = System.currentTimeMillis();
  				System.out.println("任務三耗時:"+(currentTimeMillis1-currentTimeMillis)+"ms");
  			} catch (InterruptedException e) {
  				e.printStackTrace();
  			}
  		};
  		System.out.println(Thread.currentThread().getName()+"  開啓新線程");
  		new Thread(runnable).start();
  		return "success";
  	}
  
  
  	public void task1() throws InterruptedException{
  		long currentTimeMillis = System.currentTimeMillis();
  		Thread.sleep(1000);
  		long currentTimeMillis1 = System.currentTimeMillis();
  		System.out.println("任務一耗時:"+(currentTimeMillis1-currentTimeMillis)+"ms");
  	}
  
  	public void task2() throws InterruptedException{
  		long currentTimeMillis = System.currentTimeMillis();
  		Thread.sleep(1000);
  		long currentTimeMillis1 = System.currentTimeMillis();
  		System.out.println("任務二耗時:"+(currentTimeMillis1-currentTimeMillis)+"ms");
  	}
  	public void task3() throws InterruptedException{
  		long currentTimeMillis = System.currentTimeMillis();
  		Thread.sleep(1000);
  		long currentTimeMillis1 = System.currentTimeMillis();
  		System.out.println("任務三耗時:"+(currentTimeMillis1-currentTimeMillis)+"ms");
  	}
  }
  

異步任務類

• 將異步任務單獨放到一個類中

  @Component
  public class AsyncTask {
  
  	/**
  	 * 異步-無返回值
  	 * @throws InterruptedException
  	 */
  	@Async
  	public void task1() throws InterruptedException{
  		long currentTimeMillis = System.currentTimeMillis();
  		Thread.sleep(1000);
  		long currentTimeMillis1 = System.currentTimeMillis();
  		System.out.println("任務一耗時:"+(currentTimeMillis1-currentTimeMillis)+"ms");
  	}
  	
  	@Async
  	public void task2() throws InterruptedException{
  		long currentTimeMillis = System.currentTimeMillis();
  		Thread.sleep(1000);
  		long currentTimeMillis1 = System.currentTimeMillis();
  		System.out.println("任務二耗時:"+(currentTimeMillis1-currentTimeMillis)+"ms");
  	}
  	@Async
  	public void task3() throws InterruptedException{
  		long currentTimeMillis = System.currentTimeMillis();
  		Thread.sleep(1000);
  		long currentTimeMillis1 = System.currentTimeMillis();
  		System.out.println("任務三耗時:"+(currentTimeMillis1-currentTimeMillis)+"ms");
  	}
  }
  

• 如何知道異步任務什麼時候執行完，執行的結果怎樣呢？可以採用添加Fature回調方式判斷

  /**
      	 * 異步-  future回調方式
      	 * @return
      	 * @throws InterruptedException
      	 */
      	@Async
      	public Future<String> task1s() throws InterruptedException{
      		long currentTimeMillis = System.currentTimeMillis();
      		Thread.sleep(1000);
      		long currentTimeMillis1 = System.currentTimeMillis();
      		System.out.println("任務一耗時:"+(currentTimeMillis1-currentTimeMillis)+"ms");
      		return new AsyncResult<String>("任務一執行完畢");
      	}
      
      	@Async
      	public Future<String> task2s() throws InterruptedException{
      		long currentTimeMillis = System.currentTimeMillis();
      		Thread.sleep(2000);
      		long currentTimeMillis1 = System.currentTimeMillis();
      		System.out.println("任務二耗時:"+(currentTimeMillis1-currentTimeMillis)+"ms");
      		return new AsyncResult<String>("任務二執行完畢");
      	}
      	@Async
      	public Future<String> task3s() throws InterruptedException{
      		long currentTimeMillis = System.currentTimeMillis();
      		Thread.sleep(3000);
      		long currentTimeMillis1 = System.currentTimeMillis();
      		System.out.println("任務三耗時:"+(currentTimeMillis1-currentTimeMillis)+"ms");
      		return new AsyncResult<String>("任務三執行完畢");
      	}
  

用postman進行測試：
執行異步：

同步執行：