startAsync() : Puts this request into asynchronous mode

public AsyncContext startAsync() throws IllegalStateException

Puts this request into asynchronous mode, and initializes its AsyncContext with the original ServletRequest and ServletResponse objects. Response will be delayed until you call 'complete()' method of AsyncContext.

import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.AsyncContext;

@WebServlet(urlPatterns = {"/ProcessRequest"}, asyncSupported=true)
public class ProcessRequest extends HttpServlet {
    @Override
    public void doGet(HttpServletRequest req, HttpServletResponse res)throws IOException, ServletException{
        final AsyncContext acontext = req.startAsync();
            
        String threadName = Thread.currentThread().getName();
        long startTime = System.currentTimeMillis();
        System.out.println("Thread " + threadName + " started at " + startTime);

        acontext.start(new Runnable() {
            public void run() {
                String time = req.getParameter("time");
                int wait = Integer.parseInt(time);
                    
                try{
                    Thread.sleep(wait);
                }
                catch(InterruptedException e){
                        
                }
                HttpServletResponse response = (HttpServletResponse)acontext.getResponse();
                try(PrintWriter out = response.getWriter()) {
                    out.println("I am done");
                }
                catch(Exception e){
                        
                }
                acontext.complete();
            }
        });
            
        long endTime = System.currentTimeMillis();
        System.out.println("Thread " + threadName + " finished at " + endTime);
        System.out.println("Total time taken is " +(endTime-startTime) + " Milli Seconds");
       
    }
}

Run the above servlet like below.

http://localhost:8080/servlet/ProcessRequest?time=10000

As you see the console logs, you can observe the below information messages immediately.

Info: Thread http-listener-1(5) started at 1405140693455

Info: Thread http-listener-1(5) finished at 1405140693456

Info: Total time taken is 1 Milli Seconds

After 10 seconds you can see the response in your browser.

 

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