Java API for StackExchange chat
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The purpose of this project is to provide a simple API to interact with the chat system on Stack Overflow, and the Stack Exchange network.

Maven dependency

This library is currently hosted on GitHub. To depend on it, a repository needs to be added:


The dependency is:


How to use

Joining a room

Start by creating a StackExchangeClient; this is the class used to authenticate with Stack Overflow. Give it the e-mail address you want to connect to chat with, along with the password:

StackExchangeClient client = new StackExchangeClient(emailAddress, password);

The client must be closed to log-out, by invoking client.close(). With the client, you can then join any chat room by invoking the joinRoom method, taking as first parameter the host of the chat server and, as second parameter, the id of the room to join.

Room room = client.joinRoom(ChatHost.STACK_OVERFLOW, roomId);

Once you have a Room object, you can use it to send messages or reply to other messages:

room.send("Hiya o/");
room.replyTo(messageId, "Hey!");

Each method in the Room class runs asynchronously and returns a CompletionStage that holds the result of the action. Sending a message or replying to a message returns a CompletionStage<Long> holding the id of the posted message. This allows for fluid method calls, like uploading an image and posting it as a one-box:


Listening to events

Once a Room was joined, it is possible to listen to various events on it, like a user joining the chat room or a user posting a message. All the possible events to listen to are documented in the EventType class.

Each event inherits from the Event class and gives access to several properties, like the date at which it was raised, the user that raised it and the room in which it was raised. Events related to messages further inherit from MessageEvent, giving access to the id of the message that raised the event.

For example, to listen to mentions, that is to say a message that mentioned the current logged-in user with @, the code is

room.addEventListener(EventType.USER_MENTIONED, event -> {
	Message message = event.getMessage(); // gets the message that triggered the mention 
	Room room = event.getRoom(); // gets the room in which it was made
	// ...

The same could be done to listen to replies, which are messages linked to a specific message of the current logged-in user, with the EventType.MESSAGE_REPLY constant.

Another example, showing how to listen to user joining the chat room:

room.addEventListener(EventType.USER_ENTERED, event -> {
	System.out.println("User " + event.getUserId() + " joined the room " + event.getRoomId());

Sample usage for a bot

Here's an example of using the library in order to build a simple chat bot. In this code, email and password represent the credentials the bot is going to use to log into Stack Exchange, and roomId represent the id of the room on the Chat.SO platform, which is the number at the end of the URL to access it:{roomId}.

What it does is simply listening to all messages posted, through the MESSAGE_POSTED event; it replies something to the poster if that message is "coffee" and the bot is stopped if the message is "die".

public static void main(String[] args) throws Exception {
    StackExchangeClient client = new StackExchangeClient(email, password);
    CountDownLatch countDownLatch = new CountDownLatch(1);
    Room room = client.joinRoom(ChatHost.STACK_OVERFLOW, roomId);
    room.addEventListener(EventType.MESSAGE_POSTED, e -> {
    	Message message = e.getMessage();
        switch (message.getPlainContent()) {
        case "coffee": room.replyTo(message.getId(), "Have some coffee!"); break;
        case "die": room.send("Bye."); countDownLatch.countDown(); break;
    try {
    } finally {

All of this processing happens in background threads. In this example, the main thread is kept waiting with a CountDownLatch of 1. Once "die" is posted, it reaches 0 and the main thread closes the client, causing the bot to leave the room.