Media Downloader Bot

In this example section, we will create a bot that downloads media files (photos, videos, GIFs, audio) sent by users, stores them locally, and allows users to retrieve them using special commands. This bot demonstrates file handling, custom filters, and media processing capabilities.

---

We will use different types of handlers and features:

• onMessage for handling commands and media messages
• CustomFilter for validating special retrieval commands
• File download and upload operations
• Multi threading for efficient media processing

---

Import necessary classes

MethodAnnotation

package io.github.natanimn;

import io.github.natanimn.telebof.BotClient;
import io.github.natanimn.telebof.BotContext;
import io.github.natanimn.telebof.enums.ParseMode;
import io.github.natanimn.telebof.filters.CustomFilter;
import io.github.natanimn.telebof.types.ReplyParameters;
import io.github.natanimn.telebof.types.updates.Message;
import io.github.natanimn.telebof.types.updates.Update;
import java.io.FileOutputStream;
import java.io.File;
import java.util.Arrays;

package io.github.natanimn;

import io.github.natanimn.telebof.BotClient;
import io.github.natanimn.telebof.BotContext;
import io.github.natanimn.telebof.enums.ParseMode;
import io.github.natanimn.telebof.filters.CustomFilter;
import io.github.natanimn.telebof.types.ReplyParameters;
import io.github.natanimn.telebof.types.updates.Message;
import io.github.natanimn.telebof.types.updates.Update;
import io.github.natanimn.telebof.annotations.MessageHandler;
import io.github.natanimn.telebof.enums.MessageType;
import java.io.FileOutputStream;
import java.io.File;
import java.util.Arrays;

---

Custom Filter for Command Validation

Create IsValidCommand class to validate media retrieval commands

This filter ensures that commands follow the pattern /type_fileId where type is one of: photo, video, gif, or audio.

class IsValidCommand implements CustomFilter{
    @Override
    public boolean check(Update update) {
        var text = update.message.text;
        if (!text.startsWith("/")) return false;

        var params = text.split("_");

        if (params.length == 1) return false;

        var prefix = params[0];
        var commands = new String[]{"/photo", "/video", "/gif", "/audio"};

        return Arrays.stream(commands).toList().contains(prefix);
    }
}

Explanation:

• Checks if the message starts with "/" and contains underscores
• Validates that the command prefix is one of the supported media types
• Ensures proper command format for media retrieval

---

Let us create MediaDownloader class with a constructor and initialize BotClient with 10 threads for better performance

MethodAnnotation

public class MediaDownloader {
    private BotClient bot;

    public MediaDownloader(String token){
        // Initialize bot with 10 threads for concurrent media processing
        this.bot = new BotClient.Builder(token).numThreads(10).build();

        var isValidCommand = new IsValidCommand();

        // Register handlers
        bot.onMessage(filter -> filter.commands("start"), this::start);
        bot.onMessage(filter -> filter.photo() || filter.animation() || filter.video() || filter.audio(), this::downloadMedia);
        bot.onMessage(filter -> filter.text() && filter.customFilter(isValidCommand), this::getMedia);
    }
}

public class MediaDownloader {
    private BotClient bot;

    public MediaDownloader(String token){
        // Initialize bot with 10 threads for concurrent media processing
        this.bot = new BotClient.Builder(token).numThreads(10).build();

        // Register the class as a handler
        bot.addHandler(this);
    }
}

Our bot will be handling the following events:

• /start command - Welcome message and instructions
• Media messages (photos, videos, GIFs, audio) - Download and storage
• Special retrieval commands (/photo_fileId, /video_fileId, etc.) - Media retrieval

---

Create /start handler with welcome message

MethodAnnotation

private void start(BotContext context, Message message){
    context.sendMessage(message.chat.id,
    """
    Welcome!
    I am media downloader bot. Send me photo, video, audio or gif up to 20MB;
    I will download it into my machine, and you will get it back with special command""").exec();
}

@MessageHandler(commands = "start")
private void start(BotContext context, Message message){
    context.sendMessage(message.chat.id,
    """
    Welcome! 
    I am media downloader bot. Send me photo, video, audio or gif up to 20MB; 
    I will download it into my machine, and you will get it back with special command""").exec();
}

Handle media download when user sends photos, videos, GIFs, or audio

This handler processes incoming media files, downloads them from Telegram servers, and stores them locally.

MethodAnnotation

private void downloadMedia(BotContext context, Message message) {

    // Send initial processing message as a reply to the media
    var msg = context.sendMessage(message.chat.id, "<code>Downloading media...</code>")
            .replyParameters(new ReplyParameters(message.message_id))
            .parseMode(ParseMode.HTML)
            .exec();

    String file_id, type, ext;

    // Determine media type and get the appropriate file ID
    if (message.photo != null) {
        file_id = message.photo.getLast().file_id; // Get highest quality photo
        type    = "photo";
        ext     = ".png";
    } else if (message.audio != null) {
        file_id = message.audio.file_id;
        type    = "audio";
        ext     = ".mp3";
    } else if (message.video != null) {
        file_id = message.video.file_id;
        type    = "video";
        ext     = ".mp4";
    } else {
        file_id = message.animation.file_id;
        type = "gif";
        ext = ".gif";
    }

    // Get file information and download the actual file content
    var file    = context.getFile(file_id).exec();
    byte[] data = context.downloadFile(file.file_path);

    // Save the downloaded file to local storage
    try(var stream  = new FileOutputStream(file_id + ext)){
        stream.write(data);

        // Update status message to indicate success
        context.editMessageText("<b>Media downloaded successfully!</b>", message.chat.id, msg.message_id)
                .parseMode(ParseMode.HTML)
                .exec();

        // Provide the user with the command to retrieve this media later
        context.sendMessage(message.chat.id, String.format("Send <code>/%s_%s</code> to get the media back", type, file_id))
                .parseMode(ParseMode.HTML)
                .exec();
    } catch (Exception e) {
        // Handle any errors during the download process
        context.editMessageText("An error occurred:\n\n" + e.getMessage(), message.chat.id, msg.message_id).exec();
    }
}

@MessageHandler(type = {MessageType.PHOTO, MessageType.VIDEO, MessageType.AUDIO, MessageType.ANIMATION})
private void downloadMedia(BotContext context, Message message) {

    // Send initial processing message as a reply to the media
    var msg = context.sendMessage(message.chat.id, "<code>Downloading media...</code>")
            .replyParameters(new ReplyParameters(message.message_id))
            .parseMode(ParseMode.HTML)
            .exec();

    String file_id, type, ext;

    // Determine media type and get the appropriate file ID
    if (message.photo != null) {
        file_id = message.photo.getLast().file_id; // Get highest quality photo
        type    = "photo";
        ext     = ".png";
    } else if (message.audio != null) {
        file_id = message.audio.file_id;
        type    = "audio";
        ext     = ".mp3";
    } else if (message.video != null) {
        file_id = message.video.file_id;
        type    = "video";
        ext     = ".mp4";
    } else {
        file_id = message.animation.file_id;
        type = "gif";
        ext = ".gif";
    }

    // Get file information and download the actual file content
    var file    = context.getFile(file_id).exec();
    byte[] data = context.downloadFile(file.file_path);

    // Save the downloaded file to local storage
    try(var stream  = new FileOutputStream(file_id + ext)){
        stream.write(data);

        // Update status message to indicate success
        context.editMessageText("<b>Media downloaded successfully!</b>", message.chat.id, msg.message_id)
                .parseMode(ParseMode.HTML)
                .exec();

        // Provide the user with the command to retrieve this media later
        context.sendMessage(message.chat.id, String.format("Send <code>/%s_%s</code> to get the media back", type, file_id))
                .parseMode(ParseMode.HTML)
                .exec();
    } catch (Exception e) {
        // Handle any errors during the download process
        context.editMessageText("An error occurred:\n\n" + e.getMessage(), message.chat.id, msg.message_id).exec();
    }
}

The above code explanation goes as the following:

if (message.photo != null) {
    file_id = message.photo.getLast().file_id; // Get highest quality photo
    type    = "photo";
    ext     = ".png";
}

This section handles photos by selecting the last (and highest quality) version from the available photo sizes array.

var file    = context.getFile(file_id).exec();
byte[] data = context.downloadFile(file.file_path);

These lines retrieve file information from Telegram and download the actual file content using the file path.

try(var stream  = new FileOutputStream(file_id + ext)){
    stream.write(data);

This saves the downloaded media to a local file with the appropriate extension.

context.sendMessage(message.chat.id, String.format("Send <code>/%s_%s</code> to get the media back", type, file_id))

This provides the user with a specific command they can use later to retrieve this exact media file.

Handle media retrieval using special commands

This handler processes commands in the format /type_fileId and sends back the corresponding media file.

MethodAnnotation

private void getMedia(BotContext context, Message message) {
    var param = message.text.split("_");
    var type = param[0].replace("/", ""); // Extract media type from command
    var file_id = String.join("_", Arrays.copyOfRange(param, 1, param.length)); // Reconstruct file ID
    var chat_id = message.chat.id;

    // Determine the correct file extension based on media type
    File file = switch (type){
        case "photo" -> new File(file_id + ".png");
        case "video" -> new File(file_id + ".mp4");
        case "gif" -> new File(file_id + ".gif");
        default -> new File(file_id + ".mp3"); // audio
    };

    if (file.exists()){
        // Send the appropriate media type based on the command
        switch (type){
            case "photo":
                context.sendPhoto(chat_id, file).exec();
                break;
            case "video":
                context.sendVideo(chat_id, file).exec();
                break;
            case "gif":
                context.sendAnimation(chat_id, file).exec();
                break;
            default: // audio
                context.sendAudio(chat_id, file).exec();
                break;
        }
    } else {
        context.sendMessage(chat_id, "Media not found").exec();
    }
}

@MessageHandler(type = MessageType.TEXT, filter = IsValidCommand.class)
private void getMedia(BotContext context, Message message) {
    var param = message.text.split("_");
    var type = param[0].replace("/", ""); // Extract media type from command
    var file_id = String.join("_", Arrays.copyOfRange(param, 1, param.length)); // Reconstruct file ID
    var chat_id = message.chat.id;

    // Determine the correct file extension based on media type
    File file = switch (type){
        case "photo" -> new File(file_id + ".png");
        case "video" -> new File(file_id + ".mp4");
        case "gif" -> new File(file_id + ".gif");
        default -> new File(file_id + ".mp3"); // audio
    };

    if (file.exists()){
        // Send the appropriate media type based on the command
        switch (type){
            case "photo":
                context.sendPhoto(chat_id, file).exec();
                break;
            case "video":
                context.sendVideo(chat_id, file).exec();
                break;
            case "gif":
                context.sendAnimation(chat_id, file).exec();
                break;
            default: // audio
                context.sendAudio(chat_id, file).exec();
                break;
        }
    } else {
        context.sendMessage(chat_id, "Media not found").exec();
    }
}

Explanation:

• Parses commands like /photo_BAACAgIAAxkBAAIlYmivZAV
• Reconstructs the original file ID from the command parameters
• Checks if the file exists in local storage
• Sends the appropriate media type back to the user

---

Finally, create runBot method and run the bot

public void runBot(){
    bot.startPolling();
}

public static void main(String[] args){
    final var TOKEN = System.getenv("TOKEN");
    final var downloader = new MediaDownloader(TOKEN);
    downloader.runBot();
}

---

Our Media Downloader Bot can:

• Accept and process various media types (photos, videos, GIFs, audio)
• Download files from Telegram servers and store them locally
• Provide users with specific retrieval commands for each downloaded file
• Retrieve and send back stored media files on demand
• Handle multiple media processing operations concurrently using multiple threads

The full source code can be found on examples/media_downloader