Listener Introduction

Creating listeners

Creating listeners is extremely easy in Javacord. You can either use Java 8โ€™s lambda expressions to register listeners or just create a new class for them, if putting them into a method would get too messy.

Inline Listeners

api.addMessageCreateListener(event -> {
    Message message = event.getMessage();
    if (message.getContent().equalsIgnoreCase("!ping")) {
      event.getChannel().sendMessage("Pong!");
    }
});

In their own class

api.addListener(new MyListener());

and

public class MyListener implements MessageCreateListener {

    @Override
    public void onMessageCreate(MessageCreateEvent event) {
        Message message = event.getMessage();
        if (message.getContent().equalsIgnoreCase("!ping")) {
            event.getChannel().sendMessage("Pong!");
        }
    }

}

Before logging in

Sometimes it might be useful to add listeners before calling the DiscordApiBuilder#login() method.

DiscordApi api = new DiscordApiBuilder()
        // An inline listener
        .addMessageCreateListener(event -> {
            Message message = event.getMessage();
            if (message.getContent().equalsIgnoreCase("!ping")) {
                event.getChannel().sendMessage("Pong!");
            }
        })
        .addServerBecomesAvailableListener(event -> {
            System.out.println("Loaded " + event.getServer().getName());
        })
        // A listener in their own class
        .addListener(new MyListener())
         // Alternative syntax that can be used for classes that require a DiscordApi parameter in their constructor
        .addListener(MyListener::new)
        .setToken("top secret")
        .setWaitForServersOnStartup(false)
        .login()
        .join();

Note: In most cases, itโ€™s enough to add listeners after logging in

Object listeners

Another cool feature is the ability to attach listeners directly to objects. An example where this can be useful is, for example, reacting to reactions. The following code would delete the message if someone adds a :thumbsdown: reaction.

message.addReactionAddListener(event -> {
    if (event.getEmoji().equalsEmoji("๐Ÿ‘Ž")) {
        event.deleteMessage();
    }
}).removeAfter(30, TimeUnit.MINUTES);

Seems like the bot is very sensitive to criticism.

Removing listeners

There are two ways to remove a listener:

Using the returned ListenerManager

Every time you register a listener, a ListenerManager is returned which can be used to unregister the listener:

ListenerManager<MessageCreateListener> listenerManager = api.addMessageCreateListener(event -> {
    // Do stuff
});

listenerManager.remove();

This manager also has some utility methods. You can, for example, remove a listener after a given time, which can be useful for object listeners:

message.addReactionAddListener(event -> {
  // Do stuff
}).removeAfter(30, TimeUnit.MINUTES);

Using the removeListener(...) method

You can remove any listener using the removeListener(...) method:

MyListener listener = new MyListener();
api.addListener(listener);
// ...
api.removeListener(listener);


Improve this page