Getting All messages in channel to JSON Object (IN JDA)

[YuInseo]

I am trying to save text channel's message to a file, I success to get all messages in channel
But I wonder how to get the other type Like attachment file, image, etc..

public void save(List<Message> messageHistory, long channelId, TicketStatus ticketStatus) {
        try {
            String filePath = generatePath(channelId, ticketStatus);
            File dir = new File(local, filePath);

            if (!dir.exists()) dir.mkdirs();
            File file = new File(filePath, "message.txt");

            Path logFile = Paths.get(file.getAbsolutePath());
            BufferedWriter bufferedWriter = Files.newBufferedWriter(logFile, StandardCharsets.UTF_8);

            messageHistory.forEach(message -> {
                Gson gson = new Gson();
                TicketMessage ticketMessage = new TicketMessage()
                        .setIdLong(message.getIdLong());

                String studentJson = gson.toJson(ticketMessage);
                System.out.println(studentJson);
            });

            bufferedWriter.flush();
            bufferedWriter.close();

        } catch (IOException e) {
            throw new RuntimeException(e);
        }
}