要實現佇列的順序消費，比如(1)下單(2)支付(3)支付

預設的傳送會隨機指定一個佇列，

SendResult result = producer.send(msg);

public MessageQueue selectOneMessageQueue(final TopicPublishInfo tpInfo, final String lastBrokerName) {
    return this.mqFaultStrategy.selectOneMessageQueue(tpInfo, lastBrokerName);
}

public MessageQueue selectOneMessageQueue
 
(final String lastBrokerName) {
    if (lastBrokerName == null) {
        return selectOneMessageQueue();
} else {
        int index = this.sendWhichQueue.getAndIncrement();
        for (int i = 0; i < this.messageQueueList.size(); i++) {
            int pos = Math.abs(index++) % this.messageQueueList
 
.size();
            if (pos < 0)
                pos = 0;
MessageQueue mq = this.messageQueueList.get(pos);
            if (!mq.getBrokerName().equals(lastBrokerName)) {
                return mq;
}
        }
        return selectOneMessageQueue();
}
}

就普通的roundbin，

可以自定義一個MessageQueueSelector ，然後需要實現順序消費的放到一個佇列中就行。

public SendResult send(Message msg, MessageQueueSelector selector, Object arg)
        throws MQClientException, RemotingException, MQBrokerException, InterruptedException {
    return this.defaultMQProducerImpl.send(msg, selector, arg);
}