Skip to content


Subversion checkout URL

You can clone with HTTPS or Subversion.

Download ZIP
Socket.IO Client Implementation in Java
branch: master

This branch is 32 commits ahead, 62 commits behind Gottox:master

Fetching latest commit…

Cannot retrieve the latest commit at this time

Failed to load latest commit information.


Flattr this git repo

Socket.IO-Client for Java is an easy to use implementation of for Java.

It uses Weberknecht as transport backend, but it's easy to write your own transport. See description below. An XHR-Transport is included, too. But it's not functional in its current state.

The API is inspired by


  • transparent reconnecting - The API cares about re-establishing the connection to the server when the transport is interrupted.
  • easy to use API - implement an interface, instantiate a class - you're done.
  • output buffer - send data while the transport is still connecting. No problem, handles that.
  • meaningful exceptions - If something goes wrong, SocketIO tries to throw meaningful exceptions with hints for fixing.

Status: Connecting with Websocket is production ready. XHR is not usable at the moment but I'm working on it.


  • with git

    git clone git://
  • with mercurial

    hg clone 

Both repositories are synchronized and up to date.


to build a jar-file:

ant jar
ls jar/socketio.jar

You'll find the in jar/socketio.jar


Please report any bugs feature requests to the Github issue tracker

How to use

Using is quite simple. But lets see:

        SocketIO socket = new SocketIO("");
        socket.connect(new IOCallback() {
            public void onMessage(JSONObject json, IOAcknowledge ack) {
                try {
                    System.out.println("Server said:" + json.toString(2));
                } catch (JSONException e) {

            public void onMessage(String data, IOAcknowledge ack) {
                System.out.println("Server said: " + data);

            public void onError(SocketIOException socketIOException) {
                System.out.println("an Error occured");

            public void onDisconnect() {
                System.out.println("Connection terminated.");

            public void onConnect() {
                System.out.println("Connection established");

            public void on(String event, IOAcknowledge ack, Object... args) {
                System.out.println("Server triggered event '" + event + "'");

        // This line is cached until the connection is establisched.
        socket.send("Hello Server!");

For further informations, read the Javadoc.


Read this if you want to investigate in


What is the SocketIO class?

SocketIO is the API frontend. You can use this to connect to multiple hosts. If an IOConnection object exists for a certian host, it will be reused as the specs state.


What is the IOConnection class?

This class is used to hold a connection to a server. It handles calling callback functions of the corresponding SocketIO and reconnecting if the connection is shut down ungracefully.


What is the IOTransport interface?

This interface describes a connection to a host. The implementation can be fairly minimal, as IOConnection does most of the work for you. Reconnecting, errorhandling, etc... is handled by IOConnection.


How to implement a transport?

An example can be found in or Create a class implementing the IOTransport interface.


public static final String TRANSPORT_NAME

This constant should contain the name of the transport.

static IOTransport create(URL url, IOConnection connection)

Called by IOConnector to create a new Instance of the transport. The URL is the one you should connect to. Here you can rewrite the url if needed, i.e. WebsocketTransport rewrites the incoming "http://" address to "ws://"

void connect();

Called by IOConnection. Here you should set up the connection.

void disconnect();

Called by IOConnection. This should shut down the connection. I'm currently not sure if this function is called multiple times. So make sure, it doesn't crash if it's called more than once.

void send(String text) throws IOException;

Called by IOConnection. This call request you to send data to the server.

boolean canSendBulk();

If you can send more than one message at a time, return true. If not return false.

void sendBulk(String[] texts) throws IOException;

Basicly the same as send() but for multiple messages at a time. This is only called when canSendBulk returns true.

void invalidate();

After this call, the transport should not call any methods of IOConnection. It must not disconnect from the server. This is the case when we're forcing a reconnect. If we disconnect gracefully from the server, it will terminate our session.


Ok, now we know when our functions are called. But how do we tell to process messages we get? The provided IOConnection does the trick.


Call this method when the connection is established an the socket is ready to send and receive data.


Call this method when the connection is shot down. IOConnection will care about reconnecting, if it's feasibility.

IOConnection.transportError(Exception error)

Call this method when the connection is experiencing an error. IOConnection will take care about reconnecting or throwing an error to the callbacks. Whatever makes more sense ;)

IOConnection.transportMessage(String message)

This should be called as soon as the transport has received data. IOConnection will take care about parsing the information and calling the callbacks of the sockets.

Changes to IOConnection

Now IOConnection needs to instantiate the transpost look at the sourcecode of IOConnection and search for the connectTransport() method. It's part of the ConnectThread inner class.

add a new else if branch to the section. I.e.:

    else if (protocols.contains(MyTransport.TRANSPORT_NAME))
        transport = MyTransport.create(url, IOConnection.this);


This Library was designed with portability in mind.

  • Android is fully supported.
  • JRE is fully supported.
  • GWT does not work at the moment, but a port would be possible.
  • JavaME untested.
  • ... is there anything else out there?


There comes a JUnit test suite with Currently it's tested with Eclipse.

You need node installed in PATH.

  • open the project with eclipse
  • open tests/io.socket/
  • run it as JUnit4 test.


  • needs more unit-tests.
  • XhrTransport needs to pass all tests.
  • If websockets are failing (due to proxy servers e.g.), use XHR automaticly instead.

License - the boring stuff...

This library is distributed under MIT Licence.

Something went wrong with that request. Please try again.