程序中如何连接RabbitMQ集群，与连接单节点的MQ有什么区别？

连接RabbitMQ集群与连接单节点MQ的区别在于需要指定多个节点的主机名或IP地址，以及使用负载均衡策略来均衡消息的发送和接收。具体步骤如下：

1. 配置多个RabbitMQ节点的主机名或IP地址，例如：

spring.rabbitmq.addresses=192.168.1.1,192.168.1.2,192.168.1.3

2. 使用连接工厂创建连接时，设置负载均衡策略，例如：

ConnectionFactory factory = new ConnectionFactory();
factory.setHost("192.168.1.1,192.168.1.2,192.168.1.3");
factory.setPort(5672);
factory.setVirtualHost("/");
factory.setUsername("guest");
factory.setPassword("guest");
factory.setAutomaticRecoveryEnabled(true);
factory.setNetworkRecoveryInterval(10000);
factory.setConnectionTimeout(30000);
factory.setChannelMax(100);
factory.setRequestedHeartbeat(60);
factory.setTopologyRecoveryEnabled(true);
factory.setAutomaticRecoveryEnabled(true);
factory.setConnectionTimeout(30000);
factory.setNetworkRecoveryInterval(10000);
factory.setRequestedHeartbeat(60);
factory.setSharedExecutor(Executors.newFixedThreadPool(20));
factory.setExceptionHandler(new DefaultExceptionHandler());
factory.setRecoveryDelayHandler(new RecoveryDelayHandler() {
    @Override
    public long getDelayRecoveryMillis(int attempt) {
        return 5000;
    }
});
factory.setConnectionLoadBalancer(new RoundRobinConnectionLoadBalancer(Arrays.asList(
    new Address("192.168.1.1", 5672),
    new Address("192.168.1.2", 5672),
    new Address("192.168.1.3", 5672)
)));
Connection connection = factory.newConnection();

3. 使用连接工厂创建连接后，可以创建多个channel，每个channel使用不同的负载均衡策略，例如：

Channel channel1 = connection.createChannel();
channel1.basicConsume("queue1", true, new DefaultConsumer(channel1));

Channel channel2 = connection.createChannel();
channel2.basicConsume("queue2", true, new DefaultConsumer(channel2));

Channel channel3 = connection.createChannel();
channel3.basicConsume("queue3", true, new DefaultConsumer(channel3));