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copied!<p>This is an excellent question, here is a full working example (Servlet 3.0 / Java EE 6)</p> <p>Some notes:</p> <ol> <li>it handles "browser tab / window closed" via <code>out.checkError()</code> that also calls <code>flush()</code> </li> <li>I wrote it quickly, so I'm sure it can be improved, just a POC, don't use in production before testing</li> </ol> <p><strong>Servlet:</strong> (omitted imports for brevity, will update a full gist soon)</p> <pre><code>@WebServlet(urlPatterns = {"/mySSE"}, asyncSupported = true) public class MyServletSSE extends HttpServlet { private final Queue<AsyncContext> ongoingRequests = new ConcurrentLinkedQueue<>(); private ScheduledExecutorService service; @Override public void init(ServletConfig config) throws ServletException { final Runnable notifier = new Runnable() { @Override public void run() { final Iterator<AsyncContext> iterator = ongoingRequests.iterator(); //not using for : in to allow removing items while iterating while (iterator.hasNext()) { AsyncContext ac = iterator.next(); Random random = new Random(); final ServletResponse res = ac.getResponse(); PrintWriter out; try { out = res.getWriter(); String next = "data: " + String.valueOf(random.nextInt(100) + 1) + "num of clients = " + ongoingRequests.size() + "\n\n"; out.write(next); if (out.checkError()) { //checkError calls flush, and flush() does not throw IOException iterator.remove(); } } catch (IOException ignored) { iterator.remove(); } } } }; service = Executors.newScheduledThreadPool(10); service.scheduleAtFixedRate(notifier, 1, 1, TimeUnit.SECONDS); } @Override public void doGet(HttpServletRequest req, HttpServletResponse res) { res.setContentType("text/event-stream"); res.setCharacterEncoding("UTF-8"); final AsyncContext ac = req.startAsync(); ac.setTimeout(60 * 1000); ac.addListener(new AsyncListener() { @Override public void onComplete(AsyncEvent event) throws IOException {ongoingRequests.remove(ac);} @Override public void onTimeout(AsyncEvent event) throws IOException {ongoingRequests.remove(ac);} @Override public void onError(AsyncEvent event) throws IOException {ongoingRequests.remove(ac);} @Override public void onStartAsync(AsyncEvent event) throws IOException {} }); ongoingRequests.add(ac); } } </code></pre> <p><strong>JSP:</strong></p> <pre><code><%@page contentType="text/html" pageEncoding="UTF-8"%> <!DOCTYPE html> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <title>JSP Page</title> <script> function test() { 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 />"; }; } window.addEventListener("load", test); </script> </head> <body> <h1>Hello SSE!</h1> <div id="sse"></div> </body> </html> </code></pre>

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