Building a Message Logging Bot

This guide demonstrates how to build a message logging bot that listens for messages and reactions across your Discord server.

Overview

You’ll learn how to:

Handle message events from guilds and DMs
Process reactions on messages
Work with channel types
Format and display message information

Prerequisites

Completed the Creating a Bot guide
Bot token ready
Gateway intents enabled for messages and reactions

Required Gateway Intents

This bot requires the MESSAGE_CONTENT privileged intent, which must be enabled in the Discord Developer Portal.

Message logging requires these intents:

import net.dv8tion.jda.api.requests.GatewayIntent;
import java.util.EnumSet;

EnumSet<GatewayIntent> intents = EnumSet.of(
    GatewayIntent.GUILD_MESSAGES,           // Messages in servers
    GatewayIntent.DIRECT_MESSAGES,          // Direct messages
    GatewayIntent.MESSAGE_CONTENT,          // Access to message content
    GatewayIntent.GUILD_MESSAGE_REACTIONS,  // Reactions in servers
    GatewayIntent.DIRECT_MESSAGE_REACTIONS  // Reactions in DMs
);

Complete Example

Here’s the full message logger implementation based on MessageLoggerExample.java:

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 javax.annotation.Nonnull;
import java.util.EnumSet;

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

    public static void main(String[] args) throws InterruptedException {
        String token = System.getenv("BOT_TOKEN");

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

        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());
    }

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

        // Check if message is from 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,    // %#s formats as #channel-name
                author,     // %#s formats as Username#1234 or Username
                printableContent
            );
        } else {
            // Message from a private channel
            System.out.printf(
                "[direct] %#s: %s\n",
                author,
                message.getContentDisplay()
            );
        }

        // Handle different channel types
        handleChannelTypes(channel);
    }

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

    private void handleChannelTypes(MessageChannelUnion channel) {
        // Check for text channels
        if (channel.getType() == ChannelType.TEXT) {
            System.out.println("The channel topic is " + 
                channel.asTextChannel().getTopic());
        }

        // Check for thread channels
        if (channel.getType().isThread()) {
            String channelName = channel.asThreadChannel()
                .getParentChannel()
                .getName();

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

Implementation Breakdown

Set Up the Event Listener

Create a class that extends ListenerAdapter and override the event methods you need:

public class MessageLoggerExample extends ListenerAdapter {
    @Override
    public void onMessageReceived(MessageReceivedEvent event) {
        // Handle messages
    }

    @Override
    public void onMessageReactionAdd(MessageReactionAddEvent event) {
        // Handle reactions
    }
}

Configure and Build JDA

Use createLight() for a minimal cache profile since we’re just logging:

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

Handle Message Events

Extract information from the event:

@Override
public void onMessageReceived(MessageReceivedEvent event) {
    User author = event.getAuthor();
    Message message = event.getMessage();
    MessageChannelUnion channel = event.getChannel();
    
    // Your logging logic here
}

Distinguish Between Guild and DM Messages

Use event.isFromGuild() to check the message source:

if (event.isFromGuild()) {
    String guildName = event.getGuild().getName();
    // Handle guild message
} else {
    // Handle DM
}

Working with Message Content

Getting Message Content

JDA provides different methods for accessing message content:

Message message = event.getMessage();

// Raw content with mentions intact
String raw = message.getContentRaw();
// Example: "Hello <@123456789>!"

// Display content with mentions converted to readable format
String display = message.getContentDisplay();
// Example: "Hello @Username!"

// Stripped content with mentions removed
String stripped = message.getContentStripped();
// Example: "Hello !"

Use getContentDisplay() for logging as it provides the most readable output.

Working with Reactions

Detect specific emoji reactions on messages:

import net.dv8tion.jda.api.entities.emoji.Emoji;

public class MyBot extends ListenerAdapter {
    // Define emojis using Unicode codepoints
    public static final Emoji HEART = Emoji.fromUnicode("U+2764");
    public static final Emoji THUMBS_UP = Emoji.fromUnicode("U+1F44D");

    @Override
    public void onMessageReactionAdd(MessageReactionAddEvent event) {
        Emoji emoji = event.getEmoji();
        
        if (emoji.equals(HEART)) {
            System.out.println("Someone reacted with a heart!");
        } else if (emoji.equals(THUMBS_UP)) {
            System.out.println("Someone gave a thumbs up!");
        }
    }
}

Find Unicode codepoints for emojis at Emojipedia.

Channel Type Specialization

The MessageChannelUnion can represent different channel types. Use specialization to access type-specific features:

MessageChannelUnion channel = event.getChannel();

// Check the channel type
ChannelType type = channel.getType();

switch (type) {
    case TEXT:
        // Cast to TextChannel to access text-specific features
        String topic = channel.asTextChannel().getTopic();
        System.out.println("Topic: " + topic);
        break;
    
    case VOICE:
        // Cast to VoiceChannel
        int userLimit = channel.asVoiceChannel().getUserLimit();
        break;
    
    case PRIVATE:
        // Cast to PrivateChannel
        User recipient = channel.asPrivateChannel().getUser();
        break;
}

// Check if channel is a thread
if (channel.getType().isThread()) {
    String parentName = channel.asThreadChannel()
        .getParentChannel()
        .getName();
}

Formatting Output

JDA entities support special formatting in printf:

User user = event.getAuthor();
MessageChannel channel = event.getChannel();

// %s - toString() output
System.out.printf("%s\n", user);
// Output: U:Username(123456789)

// %#s - "as tag" format for users, "#name" for channels
System.out.printf("%#s\n", user);
// Output: Username or Username#1234

System.out.printf("%#s\n", channel);
// Output: #general

Filtering Messages

Common filtering patterns:

@Override
public void onMessageReceived(MessageReceivedEvent event) {
    User author = event.getAuthor();
    
    // Ignore bot messages
    if (author.isBot()) {
        return;
    }
    
    // Ignore system messages
    if (author.isSystem()) {
        return;
    }
    
    // Only process guild messages
    if (!event.isFromGuild()) {
        return;
    }
    
    // Only process messages with content
    if (event.getMessage().getContentRaw().isEmpty()) {
        return;
    }
    
    // Your logic here
}

Best Practices

Performance Tips:

Use createLight() for logging bots that don’t need member cache
Filter out bot messages early to reduce processing
Only enable the intents you actually need

Privacy Considerations:

Be transparent about logging user messages
Store logs securely and consider data retention policies
Respect user privacy settings and Discord’s Terms of Service

Next Steps

Implement slash commands for bot configuration
Handle interactions to create moderation tools
Learn error handling for production bots

Getting Started

Core Concepts

Guides

Advanced Topics

Migration & Troubleshooting

Overview

Prerequisites

Required Gateway Intents

Complete Example

Implementation Breakdown

Working with Message Content

Getting Message Content

Working with Reactions

Channel Type Specialization

Formatting Output

Filtering Messages

Best Practices

Next Steps

Build docs developers (and LLMs) love

Getting Started

Core Concepts

Guides

Advanced Topics

Migration & Troubleshooting

​Overview

​Prerequisites

​Required Gateway Intents

​Complete Example

​Implementation Breakdown

​Working with Message Content

​Getting Message Content

​Working with Reactions

​Channel Type Specialization

​Formatting Output

​Filtering Messages

​Best Practices

​Next Steps

Build docs developers (and LLMs) love

Overview

Prerequisites

Required Gateway Intents

Complete Example

Implementation Breakdown

Working with Message Content

Getting Message Content

Working with Reactions

Channel Type Specialization

Formatting Output

Filtering Messages

Best Practices

Next Steps