@Override
    public String filterStreamId(Message message, byte[] fieldSplitter) {
        byte[] body = message.getBody();
        return new String(ByteUtil.split(body, fieldSplitter, FIELDS_LIMIT)[STREAM_INDEX]);
    }
filter message to get stream id
use the first word to set stream id string
inlong-agent/agent-plugins/src/main/java/org/apache/inlong/agent/plugin/filter/DefaultMessageFilter.java