A barebones WebSocket client and server implementation written in 100% Java.

Primary LanguageJavaMIT LicenseMIT

Java WebSockets

Build Status Javadocs Maven Central

This repository contains a barebones WebSocket server and client implementation written in 100% Java. The underlying classes are implemented java.nio, which allows for a non-blocking event-driven model (similar to the WebSocket API for web browsers).

Implemented WebSocket protocol versions are:

Here some more details about protocol versions/drafts. PerMessageDeflateExample enable the extension with reference to both a server and client example.

Getting Started

Dependency management tools

Below is a brief guide to using dependency management tools like maven or gradle.


To use maven add this dependency to your pom.xml:



To use Gradle add the maven central repository to your repositories list:


Then you can just add the latest version to your build.

compile "org.java-websocket:Java-WebSocket:1.5.7"

Or this option if you use gradle 7.0 and above.

implementation 'org.java-websocket:Java-WebSocket:1.5.7'


This library uses SLF4J for logging and does not ship with any default logging implementation.

Exceptions are using the log level ERROR and debug logging will be done with log level TRACE.

Feel free to use whichever logging framework you desire and use the corresponding binding in your dependency management.

If you want to get started, take a look at the SimpleLogger example.

Standalone jar

If you do not use any dependency management tool, you can find the latest standalone jar here.

Writing your own WebSocket Server

The org.java_websocket.server.WebSocketServer abstract class implements the server-side of the WebSocket Protocol. A WebSocket server by itself doesn't do anything except establish socket connections though HTTP. After that it's up to your subclass to add purpose.

An example for a WebSocketServer can be found in both the wiki and the example folder.

Writing your own WebSocket Client

The org.java_websocket.client.WebSocketClient abstract class can connect to valid WebSocket servers. The constructor expects a valid ws:// URI to connect to. Important events onOpen, onClose, onMessage and onError get fired throughout the life of the WebSocketClient, and must be implemented in your subclass.

An example for a WebSocketClient can be found in both the wiki and the example folder.


You can find a lot of examples here.

WSS Support

This library supports wss. To see how to use wss please take a look at the examples.

If you do not have a valid certificate in place then you will have to create a self signed one. Browsers will simply refuse the connection in case of a bad certificate and will not ask the user to accept it. So the first step will be to make a browser to accept your self signed certificate. ( https://bugzilla.mozilla.org/show_bug.cgi?id=594502 ).
If the websocket server url is wss://localhost:8000 visit the url https://localhost:8000 with your browser. The browser will recognize the handshake and allow you to accept the certificate.

The vm option -Djavax.net.debug=all can help to find out if there is a problem with the certificate.

It is currently not possible to accept ws and wss connections at the same time via the same websocket server instance.

For some reason Firefox does not allow multiple connections to the same wss server if the server uses a different port than the default port (443).

If you want to use wss on the android platform you should take a look at this.

I ( @Davidiusdadi ) would be glad if you would give some feedback whether wss is working fine for you or not.

Minimum Required JDK

Java-WebSocket is known to work with:

  • Java 8 and higher

Other JRE implementations may work as well, but haven't been tested.


Everything found in this repo is licensed under an MIT license. See the LICENSE file for specifics.