Async1.java

package async;

import java.io.IOException;

import javax.servlet.AsyncContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet(urlPatterns = "/async1", asyncSupported = true)
public class Async1 extends HttpServlet {

  private static final long serialVersionUID = 1L;

  @Override
  protected void service(final HttpServletRequest request, final HttpServletResponse response) throws ServletException, IOException {

    response.getWriter().write("Before starting job \n");
    response.getWriter().flush();

    final AsyncContext actx = request.startAsync();
    actx.setTimeout(Long.MAX_VALUE);

    Thread thread = new Thread(new HeavyTask(actx));
    thread.start();

    response.getWriter().write("After starting job \n");
    response.getWriter().flush();
  }

  class HeavyTask implements Runnable {
    AsyncContext actx;

    HeavyTask(AsyncContext actx) {
      this.actx = actx;
    }

    @Override
    public void run() {
      try {
        Thread.currentThread().setName("Job-Thread-" + actx.getRequest().getParameter("job"));
        for (int i = 0; i < 7; i++) {
          actx.getResponse().getWriter().write("Doing work (" + i + ")\n");
          Thread.sleep(1000);
          println("work " + i + " completed");
        }
        println("Job finished now dispatching...");
        actx.dispatch("/async1.jsp");
      } catch (InterruptedException e) {
        e.printStackTrace();
      } catch (IllegalStateException e) {
        e.printStackTrace();
      } catch (IOException e) {
        e.printStackTrace();
      }
    }

  }

  public static void println(String output) {
    System.out.println("[" + Thread.currentThread().getName() + "]" + output);
  }
}