jEaSSE

Java Easy SSE (Server-Sent Events) implementation (at server side).

Features:

• Minimal footprint, with no 3rd-party dependencies.
• Easily integrable with plain HTTP servlets or Vertx verticles (see below examples)
• Asynchronous operation: don't spend your server threads.
• Broadcasting mode with automatic, thread-safe management of subscribers

Maven coordinates

For Servlet >= 3.0 version

<dependency>
    <groupId>info.macias</groupId>
    <artifactId>jeasse-servlet3</artifactId>
    <version>0.11.3</version>
</dependency>

(You also need to provide the servlet-api [3.0.1,) dependencies)

For Vertx >= 3.1 Version

<dependency>
    <groupId>info.macias</groupId>
    <artifactId>jeasse-vertx3</artifactId>
    <version>0.11.3</version>
</dependency>

(You also need to provide vertx-core and vertx-web [3.1.0,) dependencies.

Usage examples

For Servlet >= 3.0

Basic, one-to-one subscription:

@WebServlet(asyncSupported = true)
public class ExampleServlet1 extends HttpServlet {

	EventTarget target;
	
	@Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
       target = new ServletEventTarget(req).ok().open();
    }

    public void onGivenEvent(String info) {
       target.send("givenEvent",info);
    }
}

Subscription to broadcast messages:

@WebServlet(asyncSupported = true)
public class ExampleServlet2 extends HttpServlet {

	EventBroadcast broadcaster = new EventBroadcast();
	
	// Attaches a subscriber
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        broadcaster.addSubscriber(new ServletEventTarget(req));
    }

    // Broadcasts a message to all the subscribers
	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		broadcaster.broadcast("message","broadcasting that I received a POST message from somebody");
	}	   
}

Subscription to broadcast messages, with individial welcome message (MessageEvent API used):

@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    MessageEvent welcome = new MessageEvent.Builder().setData("Welcome to the broadcasting service").build();
	broadcaster.addSubscriber(new ServletEventTarget(req),welcome);
}

For Vertx >= 3.1

Basic, one-to-one subscription:

Router router = Router.router(vertx);
EventTarget target;

router.get("/subscribe").handler(ctx -> {
    target = new VertxEventTarget(ctx.request());
});

router.get("/ongivenevent").handler(ctx -> {
   target.send("givenEvent","I inform you that I received a some event");
});

Subscription to broadcast messages:

Router router = Router.router(vertx);
EventBroadcast broadcaster = new EventBroadcast();

// Subscription request
router.get("/subscribe").handler(ctx -> {
    try {
        broadcaster.addSubscriber(new VertxEventTarget(ctx.request());
    } catch (Exception e) {
        e.printStackTrace();
    }
});

// Message send request
router.post("/msg").handler(ctx -> {
    broadcaster.broadcast("message","broadcasting that I have received a POST message");
});

Subscription to broadcast messages, with individial welcome message (MessageEvent API used):

router.get("/subscribe").handler(ctx -> {
    try {
        broadcaster.addSubscriber(new VertxEventTarget(ctx.request()),
                new MessageEvent.Builder().setData("Welcome to the broadcasting service").build()
                );
    } catch (Exception e) {
        e.printStackTrace();
    }
});

Example of usage

To see the easiness of integration of jEaSSe, you can see a simple chat web application in the examples folder.

Client-side libraries

At the moment I do not provide any client-side library. You can use other cool libraries:

• Jersey's EventInput
• Javascript's EventSource (Enabled by default in all browsers excepting Internet Explorer/MS Edge)
  • Implementations for Internet Explorer (https://github.com/remy/polyfills/blob/master/EventSource.js) (https://github.com/amvtek/EventSource) (https://github.com/remy/polyfills/blob/master/EventSource.js)