java - Servlet 3.0 测试查询中的异步属性

Question

我使用下面的教程在 Servlet 3.0 中实现了异步属性。

http://hmkcode.com/java-servlet-3-0-asynchronous-support/

在后端实现一个可运行类后，我观察到创建了 2 个线程，其中一个以异步方式结束，另一个执行后端处理。我能够成功实现提到的异步属性。在runnable类中，我保持了25秒的 sleep ，并且尝试在servlet类中使用outStream.println(Calendar.getInstance().getTimeInMillis())，我观察到了偏差。println中打印的时间值是请求开始时的时间，但outStream是在25秒后打印在URL命中页面上的。我只是想了解何时在 servlet 中构建打印(基于我进行此分析的时间戳)，为什么它在工作类 sleep 时间之后打印在 servlet URL 命中页面中。

 @WebServlet(name="asyncServlet",value = {"/async"},asyncSupported = true)       
public class AsyncServlet extends HttpServlet 
{
private static final long serialVersionUID = 1L;
@Override
protected void handleRequest(HttpServletRequest req, HttpServletResponse resp)
    throws ServletException, IOException {
servletoutputstream out = response.getoutputstream(); 
   final AsyncContext ctx = req.startAsync();
 ctx.addListener(new AsyncListener() {
        @Override
        public void onTimeout(AsyncEvent arg0) throws IOException {
            System.out.println("onTimeout...");             
        }

        @Override
        public void onStartAsync(AsyncEvent arg0) throws IOException {
            System.out.println("onStartAsync...");              
        }

        @Override
        public void onError(AsyncEvent arg0) throws IOException {
            System.out.println("onError...");           
        }

        @Override
        public void onComplete(AsyncEvent arg0) throws IOException {
            System.out.println("onComplete...");
        }
   });
   ctx.start(new Runnable() {
        @Override
        public void run() {
             try {
        Thread.currentThread.sleep(1000);

            } catch InterruptedException e) {
                e.printStackTrace();
            }

         ctx.complete();
        }
   });
    out.write("Got the request"+calendar.getinstance().gettimeinmillis());
out.close();
}
}

这里我打印出来，输出字符串中捕获的时间是在 sleep 时间之前，但它是在 sleep 时间之后打印的。

我尝试过使用 PrintWriter，但观察到相同的输出。有没有办法使用上面的代码在 sleep 时间之前打印响应。

Answer 1

下面是可以按照您的要求工作的代码。

     @WebServlet(name = "asyncServlet", value = { "/async" }, asyncSupported = true)
public class AsyncServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html");
    final   PrintWriter out = response.getWriter(); 

        final AsyncContext ctx = req.startAsync();
        ctx.addListener(new AsyncListener() {
            @Override
            public void onTimeout(AsyncEvent arg0) throws IOException {
                System.out.println("onTimeout...");             
            }

            @Override
            public void onStartAsync(AsyncEvent arg0) throws IOException {
                System.out.println("onStartAsync...");              
            }

            @Override
            public void onError(AsyncEvent arg0) throws IOException {
                System.out.println("onError...");           
            }

            @Override
            public void onComplete(AsyncEvent arg0) throws IOException {
                System.out.println("onComplete...");
                out.close();
            }
        });
        ctx.start(new Runnable() {
            @Override
            public void run() {
                try {
                    Thread.sleep(3000);
                }catch(InterruptedException e) {
                    e.printStackTrace();
                }
                try {
                    out.print("<br> Got the request : "+Calendar.getInstance().getTimeInMillis()+" For Async thread :"+Thread.currentThread().getName());
                    out.flush();

                } catch (Exception e) {
                    e.printStackTrace();
                }
                ctx.complete();
            }
        });
        try {
            long time=Calendar.getInstance().getTimeInMillis();
            out.print("<br>Got the request :"+time+" For Original thread completed :"+Thread.currentThread().getName());
            out.flush();
        } catch (Exception e) {
            e.printStackTrace();
        }

    }
}

输出:

Got the request :1426238802101 For Original thread completed :http-bio-8080-exec-14

3秒后:

 Got the request : 1426238805101 For Async thread :http-bio-8080-exec-9

Click here查看一个演示项目，其中包含异步 Servlet 的详细代码。