AliMQ(RocketMQ)源码(三)producer.send(message)

在producer.start()后，就可以进行消息发送了，在ProducerImpl中

    public SendResult send(Message message) {
        this.checkONSProducerServiceState(this.defaultMQProducer.getDefaultMQProducerImpl());
        com.aliyun.openservices.shade.com.alibaba.rocketmq.common.message.Message msgRMQ = ONSUtil.msgConvert(message);

        try {
            com.aliyun.openservices.shade.com.alibaba.rocketmq.client.producer.SendResult sendResultRMQ = this.defaultMQProducer.send(msgRMQ);

前面两行是检查状态和将消息转为正确的格式。核心代码是最后一行。
上面方法，最终调用了DefaultMQProducerImpl的sendDefaultImpl方法。

一、验证

这个方法的前两行还是做验证,不细究

        this.makeSureStateOK();
        Validators.checkMessage(msg, this.defaultMQProducer);

二、获取topic信息

TopicPublishInfo topicPublishInfo = this.tryToFindTopicPublishInfo(msg.getTopic());

后面会根据获取到的topic的队列，路由等信息发送消息。

三、发送消息

发送消息的代码是在一个for循环里面，最多可以重试发送3次，发送消息的代码是：

sendResult = this.sendKernelImpl(msg, mq, communicationMode, sendCallback, topicPublishInfo, timeout);

在这个sendKernelImpl方法中，先是获取到broker的地址。

String brokerAddr = this.mQClientFactory.findBrokerAddressInPublish(mq.getBrokerName());

然后调用钩子的发送消息前的方法

this.executeSendMessageHookBefore(context);

发送消息的代码如下：

                switch (communicationMode) {
                    case ASYNC:
                        Message tmpMessage = msg;
                        if (msgBodyCompressed) {
                            //If msg body was compressed, msgbody should be reset using prevBody.
                            //Clone new message using commpressed message body and recover origin massage.
                            //Fix bug:https://github.com/apache/rocketmq-externals/issues/66
                            tmpMessage = MessageAccessor.cloneMessage(msg);
                            msg.setBody(prevBody);
                        }

                        sendResult = this.mQClientFactory.getMQClientAPIImpl().sendMessage(
                            brokerAddr,
                            mq.getBrokerName(),
                            tmpMessage,
                            requestHeader,
                            timeout,
                            communicationMode,
                            sendCallback,
                            topicPublishInfo,
                            this.mQClientFactory,
                            this.defaultMQProducer.getRetryTimesWhenSendAsyncFailed(),
                            context,
                            this);
                        break;
                    case ONEWAY:
                    case SYNC:
                        sendResult = this.mQClientFactory.getMQClientAPIImpl().sendMessage(
                            brokerAddr,
                            mq.getBrokerName(),
                            msg,
                            requestHeader,
                            timeout,
                            communicationMode,
                            context,
                            this);
                        break;
                    default:
                        assert false;
                        break;
                }

有三种发送消息的方式，sync，async，oneway，默认是使用sync。在发送消息前，还设置了消息头，此处不细说。
最后进入了NettyRemotingClient的invokeSync()方法。
通过如下方式发送了消息：

    @Override
    public RemotingCommand invokeSync(String addr, final RemotingCommand request, long timeoutMillis)
        throws InterruptedException, RemotingConnectException, RemotingSendRequestException, RemotingTimeoutException {
        final Channel channel = this.getAndCreateChannel(addr);
        if (channel != null && channel.isActive()) {
            try {
                if (this.rpcHook != null) {
                    this.rpcHook.doBeforeRequest(addr, request);
                }
                RemotingCommand response = this.invokeSyncImpl(channel, request, timeoutMillis);
                if (this.rpcHook != null) {
                    this.rpcHook.doAfterResponse(RemotingHelper.parseChannelRemoteAddr(channel), request, response);
                }