Developer Partner Community

  • July 20, 2015

Java Web Application sending JSON messages through WebSocket to HTML5 browser application for real time push by Lucas Jellema

Juergen Kress
PaaS Partner Adoption

clip_image001This article describes a Java EE 7 web application that exposes a REST service that handles HTTP POST requests with JSON payload. Any message received is sent through a Web Socket to the web socket (server) endpoint that is published by a Java Class deployed as part of the web application. A static HTML page with two associated JavaScript libraries is opened in a web browser and has opened a web socket connection to this same end point. The message sent from the REST service endpoint to the web socket endpoint is pushed through the web socket to the browser and used to instantly update the web page.

The specific use case that is implemented is a simple web dashboard to monitor a movie theater: the current number of people in each of the four rooms of this movie theater is observed. The REST service receives the actual spectator count and through the two web socket interactions, this count ends up in the browser and in the visual presentation.

Below you will find a step by step instruction for implementing this use case including all required source code. The implementation uses only standard technologies: Java EE 7 (including JAX-RS and Web Socket ) and plain HTML5 and JavaScript – no special libraries are involved. The code is developed in Oracle JDeveloper (12c) and deployed to Oracle WebLogic  (12c). However, given that only standard components are used, the same code should work equally well on other containers and from other IDEs.

Note: for the use case presented in this article, a somewhat simpler solution would be possible using Server Sent Events (SSE) – a simpler and lighter weight approach than the use of web sockets. SSE is uni-directional (server to client push only) and that of course is exactly what I am doing in this particular example.

The steps will be:

· Implement the REST service to handle json payloads in HTTP Post requests

· Implement the WebSocket endpoint

· Interact from REST service endpoint with WebSocket (endpoint)

· Implement the HTML and JavaScript web application to present the live status for the movie theater based on the web socket messages

The starting point is a basic Java EE web application – with no special setup in web.xml or other files.

The final application looks like this: For JDeveloper 12c users: Read the complete article here.

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