1.使用RocketMQ进行发消息时，必须要指定topic，对于topic的设置有一个开关autoCreateTopicEnable，一般在开发测试环境中会使用默认设置autoCreateTopicEnable = true，但是这样就会导致topic的设置不容易规范管理，没有统一的审核等等，所以在正式环境中会在Broker启动时设置参数autoCreateTopicEnable = false。这样当需要增加topic时就需要在web管理界面上添加即可。
2.No route info of this topic异常是如何产生的？
当autoCreateTopicEnable=false时，DefaultMQProducerImpl.sendDefaultImpl,当发消息的时候肯定先要获取关于topic的一些信息，比如有几个消息队列，是不时有序topic，有这个topic的Broker列表等，当获取不到正确的信息时，就会抛出异常
private SendResult sendDefaultImpl(
Message msg,
final CommunicationMode communicationMode,
final SendCallback sendCallback,
final long timeout
) throws MQClientException, RemotingException, MQBrokerException, InterruptedException {
this.makeSureStateOK();
Validators.checkMessage(msg, this.defaultMQProducer);
final long invokeID = random.nextLong();
long beginTimestampFirst = System.currentTimeMillis();
long beginTimestampPrev = beginTimestampFirst;
long endTimestamp = beginTimestampFirst;
TopicPublishInfo topicPublishInfo = this.tryToFindTopicPublishInfo(msg.getTopic());
if (topicPublishInfo != null && topicPublishInfo.ok()) {
省略好多代码。。。
}
List<String> nsList = this.getmQClientFactory().getMQClientAPIImpl().getNameServerAddressList();
if (null == nsList || nsList.isEmpty()) {
throw new MQClientException(
"No name server address, please set it." + FAQUrl.suggestTodo(FAQUrl.NAME_SERVER_ADDR_NOT_EXIST_URL), null).setResponseCode(ClientErrorCode.NO_NAME_SERVER_EXCEPTION);
}
throw new MQClientException("No route info of this topic, " + msg.getTopic() + FAQUrl.suggestTodo(FAQUrl.NO_TOPIC_ROUTE_INFO),
null).setResponseCode(ClientErrorCode.NOT_FOUND_TOPIC_EXCEPTION);
} private TopicPublishInfo tryToFindTopicPublishInfo(final String topic) {
TopicPublishInfo topicPublishInfo = this.topicPublishInfoTable.get(topic);
if (null == topicPublishInfo || !topicPublishInfo.ok()) {
this.topicPublishInfoTable.putIfAbsent(topic, new TopicPublishInfo());
this.mQClientFactory.updateTopicRouteInfoFromNameServer(topic);
topicPublishInfo = this.topicPublishInfoTable.get(topic);
}
}public boolean updateTopicRouteInfoFromNameServer(final String topic) {
return updateTopicRouteInfoFromNameServer(topic, false, null);
}获取消息对应的topic信息，发请求 RemotingCommand request = RemotingCommand.createRequestCommand(RequestCode.GET_ROUTEINTO_BY_TOPIC, requestHeader);但是因为没有任何一个Broker有关于这个topic的信息，所以namesrv就会返回topic不存在，处理请求的代码在DefaultRequestProcessor的
case RequestCode.GET_ROUTEINTO_BY_TOPIC: return this.getRouteInfoByTopic(ctx, request);也就是回应码ResponseCode.TOPIC_NOT_EXIST，然后抛出异常 throw new MQClientException(response.getCode(), response.getRemark());被捕获之后退出返回false。
public boolean updateTopicRouteInfoFromNameServer(final String topic, boolean isDefault,
DefaultMQProducer defaultMQProducer) {
try {
if (this.lockNamesrv.tryLock(LOCK_TIMEOUT_MILLIS, TimeUnit.MILLISECONDS)) {
try {
TopicRouteData topicRouteData;
if (isDefault && defaultMQProducer != null) {
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 {
topicRouteData = this.mQClientAPIImpl.getTopicRouteInfoFromNameServer(topic, 1000 * 3);
}
} catch (Exception e) {
if (!topic.startsWith(MixAll.RETRY_GROUP_TOPIC_PREFIX) && !topic.equals(MixAll.DEFAULT_TOPIC)) {
log.warn("updateTopicRouteInfoFromNameServer Exception", e);
}
} finally {
this.lockNamesrv.unlock();
}
} else {
log.warn("updateTopicRouteInfoFromNameServer tryLock timeout {}ms", LOCK_TIMEOUT_MILLIS);
}
} catch (InterruptedException e) {
log.warn("updateTopicRouteInfoFromNameServer Exception", e);
}
return false;
}因为if条件不满足，所以获取默认的topic信息，注意isDefault=true，defaultMQProducer=defaultMQProducer
if (topicPublishInfo.isHaveTopicRouterInfo() || topicPublishInfo.ok()) {
return topicPublishInfo;
} else {
this.mQClientFactory.updateTopicRouteInfoFromNameServer(topic, true, this.defaultMQProducer);
topicPublishInfo = this.topicPublishInfoTable.get(topic);
return topicPublishInfo;
}3.autoCreateTopicEnable=true的作用。
当Broker启动时，TopicConfigManager初始化，这里会判断该标识，创建TBW102topic，并且在后续的心跳中把信息更新到namesrv中，这样在发消息的时候就不会抛出不存在的异常。
// MixAll.DEFAULT_TOPIC
if (this.brokerController.getBrokerConfig().isAutoCreateTopicEnable()) {
String topic = MixAll.DEFAULT_TOPIC;
TopicConfig topicConfig = new TopicConfig(topic);
this.systemTopicList.add(topic);
topicConfig.setReadQueueNums(this.brokerController.getBrokerConfig()
.getDefaultTopicQueueNums());
topicConfig.setWriteQueueNums(this.brokerController.getBrokerConfig()
.getDefaultTopicQueueNums());
int perm = PermName.PERM_INHERIT | PermName.PERM_READ | PermName.PERM_WRITE;
topicConfig.setPerm(perm);
this.topicConfigTable.put(topicConfig.getTopicName(), topicConfig);
}当从namesrv查出Topic相关的信息时，在topicRouteData2TopicPublishInfo设置消息队列数量 info.getMessageQueueList().add(mq);，调用updateTopicPublishInfo方法更新缓存topicPublishInfoTable
// 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);
}
}
}然后if (topicPublishInfo != null && topicPublishInfo.ok()) 这个条件就会符合，那个异常就不会抛出。
4.当autoCreateTopicEnable=false时，界面设置topic
MQAdminStartup启动时会设置很多命令，创建topic的类UpdateTopicSubCommand()，设置相应的信息，最后调用defaultMQAdminExt.createAndUpdateTopicConfig(addr, topicConfig);发消息RequestCode.UPDATE_AND_CREATE_TOPIC，AdminBrokerProcessor处理消息 case RequestCode.UPDATE_AND_CREATE_TOPIC: return this.updateAndCreateTopic(ctx, request);同步给其他Broker
this.brokerController.getTopicConfigManager().updateTopicConfig(topicConfig);
this.brokerController.registerBrokerAll(false, true);