SSE and Servlet 3.0

I have registered a typical SSE when page loads:

Client:

sseTest: function(){

var source = new EventSource('mySSE');
source.onopen = function(event){
console.log("eventsource opened!");
};

source.onmessage = function(event){
var data = event.data;
console.log(data);
document.getElementById('sse').innerHTML+=event.data + "<br />";
};
}

My Javascript-Debugger says, that "eventsource opened!" was successfully.

My Server Code is a Servlet 3.0:

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Random;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet(urlPatterns={"/mySSE"}, name = "hello-sse", asyncSupported=true)
public class MyServletSSE extends HttpServlet {

@Override
public void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

resp.setContentType("text/event-stream");
resp.setCharacterEncoding("UTF-8");

Random random = new Random();
PrintWriter out = resp.getWriter();

//AsyncContext aCtx = req.startAsync(req, resp);
//ServletRequest sReq = aCtx.getRequest();

String next = "data: " + String.valueOf(random.nextInt(100) + 1) + "\n\n";
//out.print("retry: 600000\n"); //set the timeout to 10 mins in milliseconds
out.write(next);
out.flush();
// do not close the stream as EventSource is listening
//out.close();
//super.doGet(req, resp);
}
}

The code works! The Client-Code triggers the doGet()-Method every 3 seconds and retrieves the new data.

Questions: However, I wonder how I can make this code better by using new Servlet 3.0 Futures such as Async-Support or asyncContext.addListener(asyncListener) or something else which I do not know. As I never closes the stream, I wonder how my server wil