private void initialTransaction() {
    this.transactionalMessageService = ServiceProvider.loadClass(ServiceProvider.TRANSACTION_SERVICE_ID, TransactionalMessageService.class);
    if (null == this.transactionalMessageService) {
        this.transactionalMessageService = new TransactionalMessageServiceImpl(new TransactionalMessageBridge(this, this.getMessageStore()));
        LOG.warn("Load default transaction message hook service: {}", TransactionalMessageServiceImpl.class.getSimpleName());
    }
    this.transactionalMessageCheckListener = ServiceProvider.loadClass(ServiceProvider.TRANSACTION_LISTENER_ID, AbstractTransactionalMessageCheckListener.class);
    if (null == this.transactionalMessageCheckListener) {
        this.transactionalMessageCheckListener = new DefaultTransactionalMessageCheckListener();
        LOG.warn("Load default discard message hook service: {}", DefaultTransactionalMessageCheckListener.class.getSimpleName());
    }
    this.transactionalMessageCheckListener.setBrokerController(this);
    this.transactionalMessageCheckService = new TransactionalMessageCheckService(this);
}

public interface TransactionalMessageService {
    //用于保存Half事務消息
    PutMessageResult prepareMessage(MessageExtBrokerInner messageInner);
    CompletableFuture<PutMessageResult> asyncPrepareMessage(MessageExtBrokerInner messageInner);
    //刪除事務消息
    boolean deletePrepareMessage(MessageExt messageExt);
    //提交事務消息
    OperationResult commitMessage(EndTransactionRequestHeader requestHeader);
    //回滾事務消息
    OperationResult rollbackMessage(EndTransactionRequestHeader requestHeader);
    void check(long transactionTimeout, int transactionCheckMax, AbstractTransactionalMessageCheckListener listener);
    //打開事務消息
    boolean open();
    //關閉事務消息
    void close();
}

//獲取擴展字段的值，若是該值為true則為事務消息
String traFlag = oriProps.get(MessageConst.PROPERTY_TRANSACTION_PREPARED);
boolean sendTransactionPrepareMessage = false;
if (Boolean.parseBoolean(traFlag)
    && !(msgInner.getReconsumeTimes() > 0 && msgInner.getDelayTimeLevel() > 0)) { 
    //判斷當前Broker配置是否支持事務消息
    if (this.brokerController.getBrokerConfig().isRejectTransactionMessage()) {
        response.setCode(ResponseCode.NO_PERMISSION);
        response.setRemark(
            "the broker[" + this.brokerController.getBrokerConfig().getBrokerIP1()
                + "] sending transaction message is forbidden");
        return response;
    }
    sendTransactionPrepareMessage = true;
}

if (sendTransactionPrepareMessage) {
    //保存Half信息
    putMessageResult = this.brokerController.getTransactionalMessageService().prepareMessage(msgInner);
} else {
    putMessageResult = this.brokerController.getMessageStore().putMessage(msgInner);
}

private MessageExtBrokerInner parseHalfMessageInner(MessageExtBrokerInner msgInner) {
    //將原消息的topic保存在擴展字段中
    MessageAccessor.putProperty(msgInner, MessageConst.PROPERTY_REAL_TOPIC, msgInner.getTopic());
    //將原消息的QueueId保存在擴展字段中
    MessageAccessor.putProperty(msgInner, MessageConst.PROPERTY_REAL_QUEUE_ID,
        String.valueOf(msgInner.getQueueId()));
    //將原消息的SysFlag保存在擴展字段中
    msgInner.setSysFlag(
        MessageSysFlag.resetTransactionValue(msgInner.getSysFlag(), MessageSysFlag.TRANSACTION_NOT_TYPE));
    //修改topic的值為RMQ_SYS_TRANS_HALF_TOPIC
    msgInner.setTopic(TransactionalMessageUtil.buildHalfTopic());
    //修改Queueid為0
    msgInner.setQueueId(0);
    msgInner.setPropertiesString(MessageDecoder.messageProperties2String(msgInner.getProperties()));
    return msgInner;
}

final int tranType = MessageSysFlag.getTransactionValue(msgInner.getSysFlag());
switch (tranType) {
    // Prepared and Rollback message is not consumed, will not enter the consume queue
    case MessageSysFlag.TRANSACTION_PREPARED_TYPE:
    case MessageSysFlag.TRANSACTION_ROLLBACK_TYPE:
        queueOffset = 0L;
        break;
    case MessageSysFlag.TRANSACTION_NOT_TYPE:
    case MessageSysFlag.TRANSACTION_COMMIT_TYPE:
    default:
        break;
}