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
@Controllerpublic 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
@Controllerpublic 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; }}
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