rocketmq如何新增topic

新增topic是需要客户端直接通知broker完成的：

通过createAndUpdateTopicConfig方法 发送给broker以后，在AdminBrokerProcessor里面负责处理这个类型消息：

   private synchronized RemotingCommand updateAndCreateTopic(ChannelHandlerContext ctx,
        RemotingCommand request) throws RemotingCommandException {
        final RemotingCommand response = RemotingCommand.createResponseCommand(null);
        final CreateTopicRequestHeader requestHeader =
            (CreateTopicRequestHeader) request.decodeCommandCustomHeader(CreateTopicRequestHeader.class);
        log.info("updateAndCreateTopic called by {}", RemotingHelper.parseChannelRemoteAddr(ctx.channel()));

        if (requestHeader.getTopic().equals(this.brokerController.getBrokerConfig().getBrokerClusterName())) {
            String errorMsg = "the topic[" + requestHeader.getTopic() + "] is conflict with system reserved words.";
            log.warn(errorMsg);
            response.setCode(ResponseCode.SYSTEM_ERROR);
            response.setRemark(errorMsg);
            return response;
        }

        try {
            response.setCode(ResponseCode.SUCCESS);
            response.setOpaque(request.getOpaque());
            response.markResponseType();
            response.setRemark(null);
            ctx.writeAndFlush(response);
        } catch (Exception e) {
            log.error("Failed to produce a proper response", e);
        }

        TopicConfig topicConfig = new TopicConfig(requestHeader.getTopic());
        topicConfig.setReadQueueNums(requestHeader.getReadQueueNums());
        topicConfig.setWriteQueueNums(requestHeader.getWriteQueueNums());
        topicConfig.setTopicFilterType(requestHeader.getTopicFilterTypeEnum());
        topicConfig.setPerm(requestHeader.getPerm());
        topicConfig.setTopicSysFlag(requestHeader.getTopicSysFlag() == null ? 0 : requestHeader.getTopicSysFlag());

        this.brokerController.getTopicConfigManager().updateTopicConfig(topicConfig);

        this.brokerController.registerIncrementBrokerData(topicConfig,this.brokerController.getTopicConfigManager().getDataVersion());

        return null;

　

在updateTopicConfig方法：

    public void updateTopicConfig(final TopicConfig topicConfig) {
        TopicConfig old = this.topicConfigTable.put(topicConfig.getTopicName(), topicConfig);
        if (old != null) {
            log.info("update topic config, old:[{}] new:[{}]", old, topicConfig);
        } else {
            log.info("create new topic [{}]", topicConfig);
        }

        this.dataVersion.nextVersion();

        this.persist();
    }

　　TopicConfig是复写了equal方法的，所以可以明确知道一个topci是否真的需要改变，如果需要，那么更改版本、持久化。

　　在后面的registerIncrementBrokerData方法中还要进一步注册到broker里面。

　　注册中心是不会持久化topic的，都是broker负责持久化，启动的时候注册到nameserver，除此之外还有定时任务定期注册到注册中心。