Websocket client library for GWT
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Latest commit b1c0ba9 Mar 8, 2016 @sksamuel Update README.md



A simple GWT wrapper for javascript websockets which enable you to avoid writing native javascript code. This is not a fully featured client/server framework for websockets. Instead it is a simple wrapper for client side code when you need to connect to an existing websocket server. For example, this library was built because I needed to connect a mobile GWT webapp to a Java websocket system that used Apache Camel.

This library has no dependancy outside of the standard GWT distribution.

To use add this dependancy to your project (hosted on maven central):


Then update your .gwt.xml files to include this:

<inherits name="com.sksamuel.gwt.GwtWebsockets" />

Getting Started

To create a websocket in your code, use

Websocket socket = new Websocket("ws://hostname:port/path");

Then attach one or more listeners which are used for the callbacks:

socket.addListener(new WebsocketListener() {

    public void onClose(CloseEvent event) {
	    // do something on close

    public void onMessage(String msg) {
        // a message is received

    public void onOpen() {
        // do something on open

When the socket is successfully connected, the onOpen() callback will be invoked on each of your listeners. Similarly, for onClose() and onMessage(String). Note: You can add as many listeners as you want, and you can remove/add while the socket is open.

To open a websocket use socket.open();

To close a websocket socket.close();

To send a message to the websocket server socket.send("My message");

Sometimes you might want to check if websockets are available on your target system. For this you can use the static method Websocket.isSupported() which returns true if websockets are available.

You can create as many websockets as you want on a single page. The library takes care of assigning each one to a different javascript global.

Finally, you can get the status of the socket using the method socket.getState() which returns an integer for the current state of the socket, where CONNECTING = 0, OPEN = 1, CLOSING = 2, CLOSED = 3.

Have fun.

Binary support

Version 1.0.1 adds support for byte methods for sending and receiving. To send, simply use send(byte[]) method on Websocket. To receive, you must implement BinaryWebsocketListener instead of WebsocketListener and then you have a new callback method onMessage(byte[]).

Because binary support on websockets isn't yet supported on all browsers, this modules sends binary data using base64.


This software is licensed under the Apache 2 license, quoted below.

Copyright 2013 Stephen Samuel

Licensed under the Apache License, Version 2.0 (the "License"); you may not
use this file except in compliance with the License. You may obtain a copy of
the License at


Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
License for the specific language governing permissions and limitations under
the License.