JDK21升级后Discord Webhook发送JSON消息失败求助

将Java版本从JDK17升级至JDK21后，Discord Webhook无法发送带Embed的JSON格式消息，但纯文本消息发送正常。报错提示请求体包含无效JSON（错误码50109），但生成的JSON经校验结构无误。以下是相关错误日志、消息构建代码及发送方法代码，需排查问题原因。

错误日志 #

Failed to send webhook. Response code: 400
Response: {"message": "The request body contains invalid JSON.", "code": 50109}

Message: {"tts":false,"embeds":[{"color":0,"title":"Rare drop received!","type":"rich","fields":[]}],"content":"Rare drop received: message!"}
Sent: {"tts":false,"embeds":[{"color":0,"title":"Rare drop received!","type":"rich","fields":[]}],"content":"Rare drop received: message!"}
Got: {"message": "The request body contains invalid JSON.", "code": 50109}

消息构建代码 #

Message message = new Message();

Embed embedMessage = new Embed();
String mode = "";
switch (player.getGameMode()) {
    case IRONMAN:
        mode = "[Ironman] ";
        break;
    case HARDCORE_GROUP_IRONMAN:
        mode = "[Hardcore Group Ironman] ";
        break;
    case GROUP_IRONMAN:
        mode = "[Group Ironman] ";
        break;
    case HARDCORE_IRONMAN:
        mode = "[Hardcore Ironman] ";
        break;
    case ULTIMATE_IRONMAN:
        mode = "[Ultimate Ironman] ";
        break;
}
System.out.println("sendDiscordMessage3");
embedMessage.setTitle(mode + "Rare drop received!");
String npcdesc = npcDescriptiveName == null ? "" : " from " + npcDescriptiveName;
embedMessage.setDescription(discordMessage + npcdesc + "!");
embedMessage.setColor(8917522);

Thumbnail thumbnail = new Thumbnail();
thumbnail.setUrl("https://static.runelite.net/cache/item/icon/" + itemId + ".png");
embedMessage.setThumbnail(thumbnail);

Footer footer = new Footer();
if(killcount == -1)
    footer.setText("");
else
    footer.setText(player.getDifficulty().Name + " mode" + " - KC: " + killcount + ".");
embedMessage.setFooter(footer);


System.out.println("Sending Discord message: " + message.toJson());
message.setEmbeds(embedMessage);
message.setContent("Rare drop received: " + discordMessage + "!");
webhook.sendMessage(message.toJson());

消息发送方法代码 #

public void sendMessage(JSONObject message) {
    try {
        // Convert the JSON message to a string
        String messageString = message.toString();

        // Create the HttpRequestWithBody object
        HttpRequestWithBody request = Unirest.post(url)
                .header("Content-Type", "application/json");

        // Set the request body
        request.body(messageString);

        // Make the HTTP request
        HttpResponse<String> res = request.asString();

        if (res.getStatus() == 200) {
            System.out.println("Webhook sent successfully.");
        } else {
            System.out.println("Failed to send webhook. Response code: " + res.getStatus());
            System.out.println("Response: " + res.getBody());
            System.out.println("Message: " + messageString);
        }

        if (verbose) {
            System.out.println("Sent: " + messageString);
            System.out.println("Got: " + res.getBody());
        }
    } catch (UnirestException e) {
        ServerWrapper.logError("Failed to send webhook: " + message.toString(), e);
    }
}

排查分析与解决方案 #

可能原因 #

1. 空字段序列化异常：JDK21环境下，JSON序列化可能将空字符串字段（如footer的空text）转为null，或保留无效空字段结构，触发Discord的JSON校验。
2. JSON库兼容性问题：使用的JSON处理组件（如Unirest依赖的库）在JDK21下存在兼容bug，生成的JSON存在隐性语法错误（如转义、编码问题）。
3. 请求编码不明确：JDK21默认HTTP编码变更，导致发送的JSON编码不符合Discord要求。

解决步骤 #

1. 优化空字段处理：

   • 打印message.toJson()的完整输出，确认空值字段是否为Discord允许的格式（如空字符串而非null）。
   • 修改Embed构建逻辑：当footer.text为空时，直接不设置footer字段，避免生成无效空结构。

2. 更换可靠的JSON序列化方式：

   • 放弃JSONObject.toString()，改用Jackson或Gson手动序列化，同时配置忽略空值字段：

     // Gson示例
     Gson gson = new GsonBuilder().serializeNulls(false).create();
     String messageString = gson.toJson(message);
     

3. 明确请求编码：

   • 在Unirest请求中指定UTF-8编码：

     HttpRequestWithBody request = Unirest.post(url)
             .header("Content-Type", "application/json; charset=UTF-8");
     

4. 升级Unirest版本：

   • 更换为支持JDK21的最新Unirest版本，解决旧版本与JDK21的兼容性问题。

内容的提问来源于stack exchange，提问作者Reprisal Gaming