Receiving Java WebSocket Messages in JavaScript

Integrating WebSocket Communication with JavaScript and Stomp

Hello, fellow developers! Today, I’d like to share with you a little odyssey I embarked on while trying to implement WebSocket communication in a JavaScript application. The goal was to make the application listen to a specific WebSocket channel, but despite my best efforts, I was hitting a snag. This turned into a great learning opportunity that I think could be helpful to others.

Background and Setup

In my project setup, I was using Stomp over WebSockets to facilitate message exchange between a Java backend (Spring application) and a JavaScript frontend. The primary aim was to receive real-time updates from the server via a channel specific to a user or resource—pretty standard for real-time applications.

The Problem

Despite having the WebSocket connection seemingly established without any issues—as indicated by the console logging “WebSocket onopen”—my JavaScript application was not able to receive messages sent from my Java service. Something was amiss, and it wasn’t immediately obvious what was going wrong.

Initial JavaScript Implementation

Looking back at the initial setup:

1. I instantiated a WebSocket connection.

1. I also initialized a Stomp client incorrectly, and attempted to bind it with the WebSocket.

Here was my initial code block:

const socket = new WebSocket('ws://localhost:8080/gs-guide-websocket');
socket.onopen = function() {
    // Initialize Stomp Client incorrectly
    const stompClient = new StompJs.Client({
        brokerURL: 'ws://localhost:8080/gs-guide-websocket'
    });
    // Attempt to activate and connect the client
    stompClient.activate();
};

The Flaw in the WebSocket and Stomp Integration

The critical mistake here was my misunderstanding of how Stomp.js should be integrated with WebSockets. I incorrectly mixed up the instantiation and usage of raw WebSocket and Stomp client from @stomp/stompjs. The StompJs.Client() constructor does not accept a WebSocket instance but rather requires configuration parameters.

Correcting the Stomp Client Initialization

The Stomp client should be correctly initialized with the brokerURL already specified in its configuration object. Here is the corrected method:

function setupWebSocket() {
    const stompClient = new StompJs.Client({
        brokerURL: 'ws://localhost:8080/gs-guide-websocket',
        onConnect: function() {
            console.log('Websocket connected!');
            stompClient.subscribe('/topic/cards/1', function(message){
                console.log('Received:', message.body);
            });
        }
    });

    stompClient.activate();
}

Ensuring That Message Routing Is Correct

On the server side, when sending messages to this WebSocket channel, it’s crucial that the destination matches one of the prefixes configured in the server’s MessageBrokerRegistry. In this scenario, the server was configured to use “/app” for application-specific destinations, and messages were being sent to “/app/cards/1”.

Ensure that your client subscribes to a destination that the server recognizes and routes correctly. My earlier confusion was partially due to mistaking these routing configurations.

Running and Testing

Testing the application again with these corrections, I was able to see the messages being received in the browser’s console, confirming that not only was the WebSocket connection alive and well, but messages were being routed and handled correctly.

Learning and Moving Forward

This experience really hammered home two crucial points for working with WebSockets and Stomp in a JavaScript environment:

• Correct initialization and configuration of the Stomp client are key.

• Matching the message routing and subscription endpoints between the server and client is crucial for the successful delivery of messages.

This little WebSocket integration adventure, while frustrating at first, clarified a lot of concepts for me. If you’re diving into similar waters, I hope sharing this makes your journey smoother!