企业中一般都会封装rocketmq 同步 异步 单向方法，你只需要配置好nameserver地址 topic tag 消息体等，然后调用封装方法进行发送即可。
流程差不多如下
1、导入mq依赖
<dependency>
<groupId>org.apache.rocketmq</groupId>
<artifactId>rocketmq-client</artifactId>
<version>4.8.0</version>
</dependency>
2、消息发送者步骤
创建消息生成者producer，指定组名
指定Nameserver mq地址
启动生产者
创建消息对象，指定Topic、Tag和消息体
发送消息
关闭生产者
3、消费者步骤
创建消费者Consumer，指定组名
指定Nameserver地址
订阅主题Topic和Tag
（listener监听消息，去消费先到的消息）
设置回调函数，处理消息
启动消费者
同步 异步 单向底层区别
//同步
SendResult send = producer.send(msg);
//异步
producer.send(msg, new SendCallback() {
@Override
public void onSuccess(SendResult sendResult) {
System.out.println("===" + sendResult);
}
@Override
public void onException(Throwable throwable) {
System.out.println("e:" + throwable);
}
});
//单向
producer.sendOneway(msg);
异步相对同步来说send方法多了些参数SendCallback sendCallback。而这个sendCallback重写的方法有成功和失败的方法。
单向相对同步来说换了一个方法sendOneway.
在跟踪源码去看到
异步
同步
具体实现方法
一下源码传参异步，单向的区别在
int timesTotal = communicationMode == CommunicationMode.SYNC ? 1 + this.defaultMQProducer.getRetryTimesWhenSendFailed() : 1;
以及switch里面
switch(communicationMode) {
case ASYNC:
return null;
case ONEWAY:
return null;
case SYNC:
if (sendResult.getSendStatus() == SendStatus.SEND_OK || !this.defaultMQProducer.isRetryAnotherBrokerWhenNotStoreOK()) {
return sendResult;
}
default:
break label122;
}
具体如下
sendDefaultImpl方法（核心：所有同步、异步、单向）
private SendResult sendDefaultImpl(Message msg, CommunicationMode communicationMode, SendCallback sendCallback, long timeout) throws MQClientException, RemotingException, MQBrokerException, InterruptedException {
//校验 Producer 处于运行状态
this.makeSureStateOK();
//校验消息格式
Validators.checkMessage(msg, this.defaultMQProducer);
long invokeID = this.random.nextLong();
long beginTimestampFirst = System.currentTimeMillis();
long beginTimestampPrev = beginTimestampFirst;
//获取Topic路由信息
TopicPublishInfo topicPublishInfo = this.tryToFindTopicPublishInfo(msg.getTopic());
if (topicPublishInfo != null && topicPublishInfo.ok()) {
boolean callTimeout = false;
//发送的队列
MessageQueue mq = null;
//异常
Exception exception = null;
//最后一次发送结果
SendResult sendResult = null;
//计算调用发送消息到成功为止的最大次数：同步、单向调用一次 ；异步3次
int timesTotal = communicationMode == CommunicationMode.SYNC ? 1 + this.defaultMQProducer.getRetryTimesWhenSendFailed() : 1;
//第几次发送
int times = 0;
//存储每次发送消息现在broker
String[] brokersSent = new String[timesTotal];
while(true) {
label122: {
String info;
if (times < timesTotal) {
info = null == mq ? null : mq.getBrokerName();
//选择要发送的消息队列
MessageQueue mqSelected = this.selectOneMessageQueue(topicPublishInfo, info);
if (mqSelected != null) {
mq = mqSelected;
brokersSent[times] = mqSelected.getBrokerName();
long endTimestamp;
try {
beginTimestampPrev = System.currentTimeMillis();
long costTime = beginTimestampPrev - beginTimestampFirst;
if (timeout >= costTime) {
//Kernel内核的意思，调用发送消息核心方法
sendResult = this.sendKernelImpl(msg, mq, communicationMode, sendCallback, topicPublishInfo, timeout - costTime);
endTimestamp = System.currentTimeMillis();
//更新Broker可用性信息，在选择发送到的消息队列时，会参考Broker发送消息的延迟。源码多次操作Broker,可见不懂Broker就无法真正理解mq源码。
this.updateFaultItem(mq.getBrokerName(), endTimestamp - beginTimestampPrev, false);
switch(communicationMode) {
case ASYNC:
return null;
case ONEWAY:
return null;
case SYNC:
if (sendResult.getSendStatus() == SendStatus.SEND_OK || !this.defaultMQProducer.isRetryAnotherBrokerWhenNotStoreOK()) {
return sendResult;
}
default:
break label122;
}
}
callTimeout = true;
} catch (RemotingException var26) {
//当抛出RemotingException时，如果进行消息发送失败重试，则可能导致消息发送重复。例如，发送消息超时(RemotingTimeoutException)，实际Broker接收到该消息并处理成功。因此，Consumer在消费时，需要保证幂等性。
//这也是我们在生产环境看到可能出现多次重复发送的情况。
//更新Broker可用信息，更新继续循环
endTimestamp = System.currentTimeMillis();
this.updateFaultItem(mqSelected.getBrokerName(), endTimestamp - beginTimestampPrev, true);
this.log.warn(String.format("sendKernelImpl exception, resend at once, InvokeID: %s, RT: %sms, Broker: %s", invokeID, endTimestamp - beginTimestampPrev, mqSelected), var26);
this.log.warn(msg.toString());
exception = var26;
break label122;
} catch (MQClientException var27) {
//更新Broker可用信息，继续循环
endTimestamp = System.currentTimeMillis();
this.updateFaultItem(mqSelected.getBrokerName(), endTimestamp - beginTimestampPrev, true);
this.log.warn(String.format("sendKernelImpl exception, resend at once, InvokeID: %s, RT: %sms, Broker: %s", invokeID, endTimestamp - beginTimestampPrev, mqSelected), var27);
this.log.warn(msg.toString());
exception = var27;
break label122;
} catch (MQBrokerException var28) {
//更新Broker可用信息，部分情况下异常返回，结束循环
endTimestamp = System.currentTimeMillis();
this.updateFaultItem(mqSelected.getBrokerName(), endTimestamp - beginTimestampPrev, true);
this.log.warn(String.format("sendKernelImpl exception, resend at once, InvokeID: %s, RT: %sms, Broker: %s", invokeID, endTimestamp - beginTimestampPrev, mqSelected), var28);
this.log.warn(msg.toString());
exception = var28;
switch(var28.getResponseCode()) {
case 1:
case 14:
case 16:
case 17:
case 204:
case 205:
break label122;
//如果有发送结果，返回，没有，抛出异常
default:
if (sendResult != null) {
return sendResult;
}
throw var28;
}
} catch (InterruptedException var29) {
endTimestamp = System.currentTimeMillis();
this.updateFaultItem(mqSelected.getBrokerName(), endTimestamp - beginTimestampPrev, false);
this.log.warn(String.format("sendKernelImpl exception, throw exception, InvokeID: %s, RT: %sms, Broker: %s", invokeID, endTimestamp - beginTimestampPrev, mqSelected), var29);
this.log.warn(msg.toString());
this.log.warn("sendKernelImpl exception", var29);
this.log.warn(msg.toString());
throw var29;
}
}
}
if (sendResult != null) {
return sendResult;
}
info = String.format("Send [%d] times, still failed, cost [%d]ms, Topic: %s, BrokersSent: %s", times, System.currentTimeMillis() - beginTimestampFirst, msg.getTopic(), Arrays.toString(brokersSent));
info = info + FAQUrl.suggestTodo("http://rocketmq.apache.org/docs/faq/");
MQClientException mqClientException = new MQClientException(info, (Throwable)exception);
if (callTimeout) {
throw new RemotingTooMuchRequestException("sendDefaultImpl call timeout");
}
if (exception instanceof MQBrokerException) {
mqClientException.setResponseCode(((MQBrokerException)exception).getResponseCode());
} else if (exception instanceof RemotingConnectException) {
mqClientException.setResponseCode(10001);
} else if (exception instanceof RemotingTimeoutException) {
mqClientException.setResponseCode(10002);
} else if (exception instanceof MQClientException) {
mqClientException.setResponseCode(10003);
}
throw mqClientException;
}
++times;
}
} else {
List<String> nsList = this.getmQClientFactory().getMQClientAPIImpl().getNameServerAddressList();
if (null != nsList && !nsList.isEmpty()) {
throw (new MQClientException("No route info of this topic, " + msg.getTopic() + FAQUrl.suggestTodo("http://rocketmq.apache.org/docs/faq/"), (Throwable)null)).setResponseCode(10005);
} else {
throw (new MQClientException("No name server address, please set it." + FAQUrl.suggestTodo("http://rocketmq.apache.org/docs/faq/"), (Throwable)null)).setResponseCode(10004);
}
}
}但是异步是在该sendDefaultImpl方法之前做一个异步处理
ExecutorService ：那么mq异步用了线程池来提高异步请求的效率！！
@Deprecated
public void send(final Message msg, final SendCallback sendCallback, final long timeout) throws MQClientException, RemotingException, InterruptedException {
final long beginStartTime = System.currentTimeMillis();
ExecutorService executor = this.getCallbackExecutor();
try {
executor.submit(new Runnable() {
public void run() {
long costTime = System.currentTimeMillis() - beginStartTime;
if (timeout > costTime) {
try {
DefaultMQProducerImpl.this.sendDefaultImpl(msg, CommunicationMode.ASYNC, sendCallback, timeout - costTime);
} catch (Exception var4) {
sendCallback.onException(var4);
}
} else {
sendCallback.onException(new RemotingTooMuchRequestException("DEFAULT ASYNC send call timeout"));
}
}
});
} catch (RejectedExecutionException var9) {
throw new MQClientException("executor rejected ", var9);
}
}
NettyRemotingClient定义了多线程
并没有发现是哪种特殊的多线程，因此是通用的多线程。就好比map和hashmap，最后用了map一样。倒回来看，这里是多线程执行，大大提高了运行效率，并且代码严谨和规范，有判定条件，不同程度的try catch
线程池执行sendSelectImpl方法，传了msg,async异步，sendCallback（成功和失败的方法，发送消息不用等待响应，不管有没有成功或失败，生产者还会发送消息），timeout - costTime（最大等待时间默认3000-消耗时间）
大概看一下入参的情况
这里timeTotal默认是1，异步的时候是3,影响后面循环次数。
那么for循环里面要做什么事情呢
选择消息要发送的队列，准备发送
调用核心发送消息方法
更新Broker可用性信息
上面这个类sendDefaultImpl，有详细注释。
其实还可以继续深入下去，可以模仿rocketmq，自己写一个自定义mq框架那也是很厉害了！！！
