以下源码基于Rocket MQ 4.7.0
1. RocketMQ Topic创建机制
RocketMQ Topic创建机制分为两种：一种自动创建，一种手动创建。可以通过设置broker的配置文件来禁用或者允许自动创建。默认是开启的允许自动创建
autoCreateTopicEnable=true/false
下面会结合源码来深度分析一下自动创建和手动创建的过程。
2. 自动Topic
默认情况下，topic不用手动创建，当producer进行消息发送时，会从nameserver拉取topic的路由信息，如果topic的路由信息不存在，那么会默认拉取broker启动时默认创建好名为“TBW102”的Topic,这定义在org.apache.rocketmq.common.MixAll类中
// Will be created at broker when isAutoCreateTopicEnable
public static final String AUTO_CREATE_TOPIC_KEY_TOPIC = "TBW102";
自动创建开关是下BrokerConfig类中有一个私有变量：
@ImportantField
private boolean autoCreateTopicEnable = true;
这变量可以通过配置文件配置来进行修改，代码中的默认值为true，所以在默认的情况下Rocket MQ是会自动创建Topic的。
在Broker启动，会调用TopicConfigManager的构造方法，在构造方法中定义了一系列RocketMQ系统内置的一些系统Topic（这里只关注一下TBW102）:
{
// MixAll.AUTO_CREATE_TOPIC_KEY_TOPIC
if (this.brokerController.getBrokerConfig().isAutoCreateTopicEnable()) {
String topic = MixAll.AUTO_CREATE_TOPIC_KEY_TOPIC;
TopicConfig topicConfig = new TopicConfig(topic);
this.systemTopicList.add(topic);
topicConfig.setReadQueueNums(this.brokerController.getBrokerConfig()
.getDefaultTopicQueueNums()); //8
topicConfig.setWriteQueueNums(this.brokerController.getBrokerConfig()
.getDefaultTopicQueueNums()); //8
int perm = PermName.PERM_INHERIT | PermName.PERM_READ | PermName.PERM_WRITE;
topicConfig.setPerm(perm);
this.topicConfigTable.put(topicConfig.getTopicName(), topicConfig);
}
}
这里有 this.brokerController.getBrokerConfig().isAutoCreateTopicEnable() 这样一段代码，在开启允许自动创建的时候，会把当前Topic的信息存入topicConfigTable变量中。然后通过发送定期发送心跳包把Topic和Broker的信息发送到NameServer的RouteInfoManager中进行保存。在BrokerController中定义了这样的一个定时任务来执行这个心跳包的发送：
this.scheduledExecutorService.scheduleAtFixedRate(new Runnable() {
@Override
public void run() {
try {
BrokerController.this.registerBrokerAll(true, false, brokerConfig.isForceRegister());
} catch (Throwable e) {
log.error("registerBrokerAll Exception", e);
}
}
}, 1000 * 10, Math.max(10000, Math.min(brokerConfig.getRegisterNameServerPeriod(), 60000)), TimeUnit.MILLISECONDS);
这里就说明了如何把每个Broker的系统自定义的Topic注册到NameServer。接下来看在发送过程中如何从NameServer获取Topic的路由信息： DefaultMQProducerImpl.sendDefaultImpl
private SendResult sendDefaultImpl(
Message msg,
final CommunicationMode communicationMode,
final SendCallback sendCallback,
final long timeout
) throws MQClientException, RemotingException, MQBrokerException, InterruptedException {
//省略代码
//获取路由信息
TopicPublishInfo topicPublishInfo = this.tryToFindTopicPublishInfo(msg.getTopic());
}
通过DefaultMQProducerImpl.tryToFindTopicPublishInfo方法获取Topic的路由信息。
private TopicPublishInfo tryToFindTopicPublishInfo(final String topic) {
TopicPublishInfo topicPublishInfo = this.topicPublishInfoTable.get(topic);
//第一次从缓存中获取--肯定没有因为还没创建
if (null == topicPublishInfo || !topicPublishInfo.ok()) {
this.topicPublishInfoTable.putIfAbsent(topic, new TopicPublishInfo());
//从NameServer获取--也是没有，因为没有创建
this.mQClientFactory.updateTopicRouteInfoFromNameServer(topic);
topicPublishInfo = this.topicPublishInfoTable.get(topic);
}
if (topicPublishInfo.isHaveTopicRouterInfo() || topicPublishInfo.ok()) {
return topicPublishInfo;
} else {
//第二次从这里获取
this.mQClientFactory.updateTopicRouteInfoFromNameServer(topic, true, this.defaultMQProducer);
topicPublishInfo = this.topicPublishInfoTable.get(topic);
return topicPublishInfo;
}
}
下面来看一下 MQClientInstance.updateTopicRouteInfoFromNameServer 的方法:
public boolean updateTopicRouteInfoFromNameServer(final String topic, boolean isDefault,
DefaultMQProducer defaultMQProducer) {
//省略代码
if (isDefault && defaultMQProducer != null) {
//使用默认的TBW102 Topic获取数据
topicRouteData = this.mQClientAPIImpl.getDefaultTopicRouteInfoFromNameServer(defaultMQProducer.getCreateTopicKey(),
1000 * 3);
if (topicRouteData != null) {
for (QueueData data : topicRouteData.getQueueDatas()) {
int queueNums = Math.min(defaultMQProducer.getDefaultTopicQueueNums(), data.getReadQueueNums());
data.setReadQueueNums(queueNums);
data.setWriteQueueNums(queueNums);
}
}
} else {
//这是正常的
topicRouteData = this.mQClientAPIImpl.getTopicRouteInfoFromNameServer(topic, 1000 * 3);
}
//省略代码
}
如果isDefault=true并且defaultMQProducer不为空，从nameserver中获取默认路由信息，此时会获取所有已开启自动创建开关的broker的默认“TBW102”topic路由信息，并保存默认的topic消息队列数量。
这里会比较一下配在在 DefaultMQProducer.defaultTopicQueueNums中的默认值和TBW102中的值哪个更小。
if (topicRouteData != null) {
TopicRouteData old = this.topicRouteTable.get(topic);
boolean changed = topicRouteDataIsChange(old, topicRouteData);
if (!changed) {
changed = this.isNeedUpdateTopicRouteInfo(topic);
} else {
log.info("the topic[{}] route info changed, old[{}] ,new[{}]", topic, old, topicRouteData);
}
}
判断获取默认的是否存在，如果存在把当前的Topic的信息更新。也就是把TBW102 Topic的数据更新为自动创建的数据。
if (changed) {
TopicRouteData cloneTopicRouteData = topicRouteData.cloneTopicRouteData();
for (BrokerData bd : topicRouteData.getBrokerDatas()) {
this.brokerAddrTable.put(bd.getBrokerName(), bd.getBrokerAddrs());
}
// Update Pub info
{
TopicPublishInfo publishInfo = topicRouteData2TopicPublishInfo(topic, topicRouteData);
publishInfo.setHaveTopicRouterInfo(true);
Iterator<Entry<String, MQProducerInner>> it = this.producerTable.entrySet().iterator();
while (it.hasNext()) {
Entry<String, MQProducerInner> entry = it.next();
MQProducerInner impl = entry.getValue();
if (impl != null) {
impl.updateTopicPublishInfo(topic, publishInfo);
}
}
}
// Update sub info
{
Set<MessageQueue> subscribeInfo = topicRouteData2TopicSubscribeInfo(topic, topicRouteData);
Iterator<Entry<String, MQConsumerInner>> it = this.consumerTable.entrySet().iterator();
while (it.hasNext()) {
Entry<String, MQConsumerInner> entry = it.next();
MQConsumerInner impl = entry.getValue();
if (impl != null) {
impl.updateTopicSubscribeInfo(topic, subscribeInfo);
}
}
}
log.info("topicRouteTable.put. Topic = {}, TopicRouteData[{}]", topic, cloneTopicRouteData);
this.topicRouteTable.put(topic, cloneTopicRouteData);
return true;
}
更新本地的缓存。这样TBW102 Topic的负载和一些默认的路由信息就会被自己创建的Topic使用。这里就是整个自动创建的过程.
总结一下就是：通过使用系统内部的一个TBW102的Topic的配置来自动创建当前用户的要创建的自定义Topic。
3. 手动创建--预先创建
手动创建也叫预先创建，就是在使用Topic之前就创建，可以通过命令行或者通过RocketMQ的管理界面创建Topic。
通过界面控制台创建
项目地址： github.com/apache/rock…
TopicController主要负责Topic的管理
@RequestMapping(value = "/createOrUpdate.do", method = { RequestMethod.POST})
@ResponseBody
public Object topicCreateOrUpdateRequest(@RequestBody TopicConfigInfo topicCreateOrUpdateRequest) {
Preconditions.checkArgument(CollectionUtils.isNotEmpty(topicCreateOrUpdateRequest.getBrokerNameList()) || CollectionUtils.isNotEmpty(topicCreateOrUpdateRequest.getClusterNameList()),
"clusterName or brokerName can not be all blank");
logger.info("op=look topicCreateOrUpdateRequest={}", JsonUtil.obj2String(topicCreateOrUpdateRequest));
topicService.createOrUpdate(topicCreateOrUpdateRequest);
return true;
}
然后通过MQAdminExtImpl.createAndUpdateTopicConfig方法来创建：
@Override
public void createAndUpdateTopicConfig(String addr, TopicConfig config)
throws RemotingException, MQBrokerException, InterruptedException, MQClientException {
MQAdminInstance.threadLocalMQAdminExt().createAndUpdateTopicConfig(addr, config);
}
通过调用DefaultMQAdminExtImpl.createAndUpdateTopicConfig创建Topic
@Override
public void createAndUpdateTopicConfig(String addr, TopicConfig config) throws RemotingException, MQBrokerException,
InterruptedException, MQClientException {
this.mqClientInstance.getMQClientAPIImpl().createTopic(addr, this.defaultMQAdminExt.getCreateTopicKey(), config, timeoutMillis);
}
最后通过MQClientAPIImpl.createTopic创建Topic
public void createTopic(final String addr, final String defaultTopic, final TopicConfig topicConfig,
final long timeoutMillis)
throws RemotingException, MQBrokerException, InterruptedException, MQClientException {
CreateTopicRequestHeader requestHeader = new CreateTopicRequestHeader();
requestHeader.setTopic(topicConfig.getTopicName());
requestHeader.setDefaultTopic(defaultTopic);
requestHeader.setReadQueueNums(topicConfig.getReadQueueNums());
requestHeader.setWriteQueueNums(topicConfig.getWriteQueueNums());
requestHeader.setPerm(topicConfig.getPerm());
requestHeader.setTopicFilterType(topicConfig.getTopicFilterType().name());
requestHeader.setTopicSysFlag(topicConfig.getTopicSysFlag());
requestHeader.setOrder(topicConfig.isOrder());
RemotingCommand request = RemotingCommand.createRequestCommand(RequestCode.UPDATE_AND_CREATE_TOPIC, requestHeader);
RemotingCommand response = this.remotingClient.invokeSync(MixAll.brokerVIPChannel(this.clientConfig.isVipChannelEnabled(), addr),
request, timeoutMillis);
assert response != null;
switch (response.getCode()) {
case ResponseCode.SUCCESS: {
return;
}
default:
break;
}
throw new MQClientException(response.getCode(), response.getRemark());
}
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