AsyncServlet3.java

@WebServlet(urlPatterns = { "/AsyncServlet3" }, asyncSupported = true)
public class AsyncServlet3 extends HttpServlet {

    @EJB private Service4 service;

    protected void doGet(HttpServletRequest request, final HttpServletResponse response) throws ServletException, IOException {
...
        final AsyncContext ctx = request.startAsync(request, response);

        service.foo(s -> {
...
            pw.write("</body></html>");
            response.flushBuffer();
            ctx.complete(); // all done, free resources
...