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This example demonstrates how to listen for message events and log them to the console. It also shows how to handle message reactions.

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Overview

The Message Logger bot will:
  • Log all messages from both guilds (servers) and direct messages
  • Display formatted output with server name, channel, author, and content
  • Handle message reactions (specifically the heart emoji)
  • Demonstrate channel type specialization

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Setup

1

Configure Gateway Intents

To receive message events, you need to enable specific intents:
EnumSet<GatewayIntent> intents = EnumSet.of(
    // Enables MessageReceivedEvent for guild (also known as servers)
    GatewayIntent.GUILD_MESSAGES,
    // Enables the event for private channels (also known as direct messages)
    GatewayIntent.DIRECT_MESSAGES,
    // Enables access to message.getContentRaw()
    GatewayIntent.MESSAGE_CONTENT,
    // Enables MessageReactionAddEvent for guild
    GatewayIntent.GUILD_MESSAGE_REACTIONS,
    // Enables MessageReactionAddEvent for private channels
    GatewayIntent.DIRECT_MESSAGE_REACTIONS
);
The MESSAGE_CONTENT intent is a privileged intent. You need to enable it in the Discord Developer Portal under your bot’s settings.
2

Create the Event Listener

Extend ListenerAdapter to handle events:
public class MessageLoggerExample extends ListenerAdapter {
    public static final Emoji HEART = Emoji.fromUnicode("U+2764");

    @Override
    public void onMessageReceived(@Nonnull MessageReceivedEvent event) {
        // Handle message events
    }

    @Override
    public void onMessageReactionAdd(@Nonnull MessageReactionAddEvent event) {
        // Handle reaction events
    }
}
3

Register the Listener

Add your listener when building the JDA instance:
JDA jda = JDABuilder.createLight(token, intents)
    .addEventListeners(new MessageLoggerExample())
    .setActivity(Activity.watching("your messages"))
    .build();

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Handling Message Events

The onMessageReceived method is called whenever a message is sent in a channel your bot can see: 
@Override
public void onMessageReceived(@Nonnull MessageReceivedEvent event) {
    // The user who sent the message
    User author = event.getAuthor();
    // The channel where the message was sent
    MessageChannelUnion channel = event.getChannel();
    // The actual message
    Message message = event.getMessage();

    // Check whether the message was sent in a guild / server
    if (event.isFromGuild()) {
        String guildName = event.getGuild().getName();
        String printableContent = message.getContentDisplay();

        System.out.printf(
            "[%s] [%#s] %#s: %s\n",
            guildName,
            channel,    // The %#s makes use of the channel name
            author,     // The %#s makes use of User#getAsTag
            printableContent
        );
    } else {
        // This is a message from a private channel
        System.out.printf("[direct] %#s: %s\n", author, message.getContentDisplay());
    }
}
Use message.getContentDisplay() instead of getContentRaw() to convert mentions into readable text (e.g., @user instead of <@123456789>).

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Channel Type Specialization

Channels use a “union” type system that allows you to specialize to more concrete types: 
// Check if the channel is a text channel
if (channel.getType() == ChannelType.TEXT) {
    System.out.println("The channel topic is " + channel.asTextChannel().getTopic());
}

// Check if the channel is a thread
if (channel.getType().isThread()) {
    String channelName = channel.asThreadChannel()
        .getParentChannel()  // Get the parent channel
        .getName();

    System.out.println("This thread is part of channel #" + channelName);
}

​
Handling Reactions

You can listen for reaction events to detect when users react to messages: 
public static final Emoji HEART = Emoji.fromUnicode("U+2764");

@Override
public void onMessageReactionAdd(@Nonnull MessageReactionAddEvent event) {
    if (event.getEmoji().equals(HEART)) {
        System.out.println("A user loved a message!");
    }
}
Find Unicode codepoints for emojis at Emojipedia. For example, the red heart is U+2764.

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Complete Example

import net.dv8tion.jda.api.JDA;
import net.dv8tion.jda.api.JDABuilder;
import net.dv8tion.jda.api.entities.Activity;
import net.dv8tion.jda.api.entities.Message;
import net.dv8tion.jda.api.entities.User;
import net.dv8tion.jda.api.entities.channel.ChannelType;
import net.dv8tion.jda.api.entities.channel.unions.MessageChannelUnion;
import net.dv8tion.jda.api.entities.emoji.Emoji;
import net.dv8tion.jda.api.events.message.MessageReceivedEvent;
import net.dv8tion.jda.api.events.message.react.MessageReactionAddEvent;
import net.dv8tion.jda.api.hooks.ListenerAdapter;
import net.dv8tion.jda.api.requests.GatewayIntent;

import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.EnumSet;

import javax.annotation.Nonnull;

public class MessageLoggerExample extends ListenerAdapter {
    public static final Emoji HEART = Emoji.fromUnicode("U+2764");

    public static void main(String[] args) throws IOException {
        String token = new String(Files.readAllBytes(Paths.get(args[0])), StandardCharsets.UTF_8).trim();

        EnumSet<GatewayIntent> intents = EnumSet.of(
            GatewayIntent.GUILD_MESSAGES,
            GatewayIntent.DIRECT_MESSAGES,
            GatewayIntent.MESSAGE_CONTENT,
            GatewayIntent.GUILD_MESSAGE_REACTIONS,
            GatewayIntent.DIRECT_MESSAGE_REACTIONS
        );

        try {
            JDA jda = JDABuilder.createLight(token, intents)
                .addEventListeners(new MessageLoggerExample())
                .setActivity(Activity.watching("your messages"))
                .build();

            jda.getRestPing().queue(ping ->
                System.out.println("Logged in with ping: " + ping)
            );

            jda.awaitReady();
            System.out.println("Guilds: " + jda.getGuildCache().size());
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void onMessageReceived(@Nonnull MessageReceivedEvent event) {
        User author = event.getAuthor();
        MessageChannelUnion channel = event.getChannel();
        Message message = event.getMessage();

        if (event.isFromGuild()) {
            String guildName = event.getGuild().getName();
            String printableContent = message.getContentDisplay();

            System.out.printf(
                "[%s] [%#s] %#s: %s\n",
                guildName,
                channel,
                author,
                printableContent
            );
        } else {
            System.out.printf("[direct] %#s: %s\n", author, message.getContentDisplay());
        }

        if (channel.getType() == ChannelType.TEXT) {
            System.out.println("The channel topic is " + channel.asTextChannel().getTopic());
        }

        if (channel.getType().isThread()) {
            String channelName = channel.asThreadChannel()
                .getParentChannel()
                .getName();
            System.out.println("This thread is part of channel #" + channelName);
        }
    }

    @Override
    public void onMessageReactionAdd(@Nonnull MessageReactionAddEvent event) {
        if (event.getEmoji().equals(HEART)) {
            System.out.println("A user loved a message!");
        }
    }
}

​
Sample Output

When running, you’ll see output like: 
Logged in with ping: 42
Guilds: 3
[My Server] [#general] User#1234: Hello world!
[My Server] [#general] Bot#5678: Hi there!
[direct] Friend#9012: Hey!
A user loved a message!

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