Spring中注解方式的异步请求

一、Servlet3.0异步请求

@WebServlet(value = "/async", asyncSupported = true)
public class HelloAsyncServlet extends HttpServlet {

@Override
   protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
       //1、设置支持异步处理asyncSupported = true
       //2、开启异步模式
       System.out.println("主线程开始:" + Thread.currentThread() + "==>" + System.currentTimeMillis());
       AsyncContext startAsync = req.startAsync();
       //3、业务逻辑进行异步处理，开始异步处理
       startAsync.start(new Runnable() {
           @Override
           public void run() {
               try {
                   System.out.println("副线程开始:" + Thread.currentThread() + "==>" + System.currentTimeMillis());
                   sayHello();
                   //获取到异步的上下文
                   AsyncContext asyncContext = req.getAsyncContext();
                   startAsync.complete();
                   ServletResponse response = asyncContext.getResponse();
                   response.getWriter().write("hello async!");
                   System.out.println("副线程结束:" + Thread.currentThread() + "==>" + System.currentTimeMillis());
               } catch (Exception e) {
                   e.printStackTrace();
               }

}
       });
       System.out.println("主线程结束:" + Thread.currentThread() + "==>" + System.currentTimeMillis());
   }

public void sayHello() throws Exception {
       System.out.println(Thread.currentThread() + "processing...");
       Thread.sleep(3000);
   }
}

打印结果：

二、SpringMVC的异步请求

返回Callable

@Controller
public class AsyncController {

@ResponseBody
   @RequestMapping("/async01")
   public Callable<String> async01(){
       System.out.println("主线程开始:" + Thread.currentThread() + "==>" + System.currentTimeMillis());

Callable<String> callable = new Callable<String>() {

public String call() throws Exception {
               System.out.println("副线程开始:" + Thread.currentThread() + "==>" + System.currentTimeMillis());
               Thread.sleep(2000);
               System.out.println("副线程开始:" + Thread.currentThread() + "==>" + System.currentTimeMillis());

return "async01";
           }
       };

System.out.println("主线程结束:" + Thread.currentThread() + "==>" + System.currentTimeMillis());
       return callable;

}
}

• 控制器返回Callable

• Spring进行异步处理，将Callable提交给TaskExecutor，使用一个隔离的线程进行执行

• DispatcherServlet和所有的Filter退出Web容器的线程，但是response保持打开状态

• Callable返回结果，SpreingMVC将请求重新派发给容器，恢复之前的处理，Callable返回值就是目标方法的返回值

• 根据Callable返回的结果，SpringMVC继续进行视图渲染流程等(从收到请求到视图渲染)

输出结果：

返回DeferredResult

模拟一个消息中间件

public class DeferredResultQueue {

private static Queue<DeferredResult<Object>> queue = new ConcurrentLinkedDeque<DeferredResult<Object>>();

public static void save(DeferredResult<Object> deferredResult){
       queue.add(deferredResult);
   }

public static DeferredResult<Object> get(){
       return queue.poll();
   }
}

/createOrder请求会暂时保存DeferredResultQueue中，/create请求会获取DeferredResultQueue中的请求，进行业务逻辑的处理并返回结果

@Controller
public class AsyncController {

@ResponseBody
   @RequestMapping("/createOrder")
   public DeferredResult<Object> createOrder(){
       DeferredResult<Object> deferredResult = new DeferredResult<Object>((long)3000,"create fail");

DeferredResultQueue.save(deferredResult);

return deferredResult;
   }

@ResponseBody
   @RequestMapping("/create")
   public String create(){

String order = UUID.randomUUID().toString();
       DeferredResult<Object> deferredResult = DeferredResultQueue.get();
       deferredResult.setResult(order);
       return "success:" + order;
   }
}

来源：https://blog.csdn.net/qq_39794062/article/details/117512875