ActiveMq持久订阅必须指定clientId以及设置clientId源码分析

悠悠 2022-12-19 00:42 92阅读 0赞

创建持久订阅时的代码：

@Override
        public TopicSubscriber createDurableSubscriber(Topic topic, String name, String messageSelector, boolean noLocal) throws JMSException {
            checkClosed();
    
            if (topic == null) {
                throw new InvalidDestinationException("Topic cannot be null");
            }
    
            if (topic instanceof CustomDestination) {
                CustomDestination customDestination = (CustomDestination)topic;
                return customDestination.createDurableSubscriber(this, name, messageSelector, noLocal);
            }
    
            //该行是校验是否手动指定的clientid
            connection.checkClientIDWasManuallySpecified();
            ActiveMQPrefetchPolicy prefetchPolicy = this.connection.getPrefetchPolicy();
            int prefetch = isAutoAcknowledge() && connection.isOptimizedMessageDispatch() ? prefetchPolicy.getOptimizeDurableTopicPrefetch() : prefetchPolicy.getDurableTopicPrefetch();
            int maxPrendingLimit = prefetchPolicy.getMaximumPendingMessageLimit();
            return new ActiveMQTopicSubscriber(this, getNextConsumerId(), ActiveMQMessageTransformation.transformDestination(topic), name, messageSelector, prefetch, maxPrendingLimit,
                                               noLocal, false, asyncDispatch);
        }

如果没有手动指定，则抛异常：

在调用connetion.start()方法后，clientId如果没有手动指定，系统会默认 生成一个：

connection.start();

@Override
        public void start() throws JMSException {
            checkClosedOrFailed();
            //该方法会检查连接信息，没有clientId时会默认生成一个
            ensureConnectionInfoSent();
            if (started.compareAndSet(false, true)) {
                for (Iterator<ActiveMQSession> i = sessions.iterator(); i.hasNext();) {
                    ActiveMQSession session = i.next();
                    session.start();
                }
            }
        }

protected void ensureConnectionInfoSent() throws JMSException {
            synchronized(this.ensureConnectionInfoSentMutex) {
                // Can we skip sending the ConnectionInfo packet??
                if (isConnectionInfoSentToBroker || closed.get()) {
                    return;
                }
                //TODO shouldn't this check be on userSpecifiedClientID rather than the value of clientID?
                //设置clientid，但设置后，由于不是手动指定而是系统生成的，userSpecifiedClientID为false
                if (info.getClientId() == null || info.getClientId().trim().length() == 0) {
                    info.setClientId(clientIdGenerator.generateId());
                }
                syncSendPacket(info.copy(), getConnectResponseTimeout());
    
                this.isConnectionInfoSentToBroker = true;
                // Add a temp destination advisory consumer so that
                // We know what the valid temporary destinations are on the
                // broker without having to do an RPC to the broker.
    
                ConsumerId consumerId = new ConsumerId(new SessionId(info.getConnectionId(), -1), consumerIdGenerator.getNextSequenceId());
                if (watchTopicAdvisories) {
                    advisoryConsumer = new AdvisoryConsumer(this, consumerId);
                }
            }
        }

在上边的方法中，设置clientid，但设置后，由于不是手动指定而是系统生成的，userSpecifiedClientID为false。