简单的描述就是：P(生产者)发送消息到Q1(延时队列)，Q1的消息有过期时间，比如10s，那10s后消息过期就会触发死信，从而把消息转发到Q2（死信队列）。
解决问题场景：像商城下单，未支付时取消订单场景。下单时写一条记录入Q1,延时30分钟后转到Q2，消费Q2，检查订单，支付则不做操作，没支付则取消订单，恢复库存。
生产者代码：
public static void SendMessage() { //死信交换机 string dlxexChange = "dlx.exchange"; //死信队列 string dlxQueueName = "dlx.queue"; //消息交换机 string exchange = "direct-exchange"; //消息队列 string queueName = "delay_queue"; using (var connection = RabbitMQHelper.GetConnection()) { using (var channel = connection.CreateModel()) { //创建死信交换机 channel.ExchangeDeclare(dlxexChange, type: ExchangeType.Direct, durable: true, autoDelete: false); //创建死信队列 channel.QueueDeclare(dlxQueueName, durable: true, exclusive: false, autoDelete: false); //死信队列绑定死信交换机 channel.QueueBind(dlxQueueName, dlxexChange, routingKey: dlxQueueName); // 创建消息交换机 channel.ExchangeDeclare(exchange, type: ExchangeType.Direct, durable: true, autoDelete: false); //创建消息队列,并指定死信队列，和设置这个队列的消息过期时间为10s channel.QueueDeclare(queueName, durable: true, exclusive: false, autoDelete: false, arguments: new Dictionary<string, object> { { "x-dead-letter-exchange",dlxexChange}, //设置当前队列的DLX(死信交换机) { "x-dead-letter-routing-key",dlxQueueName}, //设置DLX的路由key，DLX会根据该值去找到死信消息存放的队列 { "x-message-ttl",10000} //设置队列的消息过期时间 }); //消息队列绑定消息交换机 channel.QueueBind(queueName, exchange, routingKey: queueName); string message = "hello rabbitmq message"; var properties = channel.CreateBasicProperties(); properties.Persistent = true; //发布消息 channel.BasicPublish(exchange: exchange, routingKey: queueName, basicProperties: properties, body: Encoding.UTF8.GetBytes(message)); Console.WriteLine($"{DateTime.Now},向队列:{queueName}发送消息:{message}"); } } }
消费者代码：
public static void Consumer() { //死信交换机 string dlxexChange = "dlx.exchange"; //死信队列 string dlxQueueName = "dlx.queue"; var connection = RabbitMQHelper.GetConnection(); { //创建信道 var channel = connection.CreateModel(); { //创建死信交换机 channel.ExchangeDeclare(dlxexChange, type: ExchangeType.Direct, durable: true, autoDelete: false); //创建死信队列 channel.QueueDeclare(dlxQueueName, durable: true, exclusive: false, autoDelete: false); //死信队列绑定死信交换机 channel.QueueBind(dlxQueueName, dlxexChange, routingKey: dlxQueueName); var consumer = new EventingBasicConsumer(channel); channel.BasicQos(prefetchSize: 0, prefetchCount: 1, global: true); consumer.Received += (model, ea) => { //处理业务 var message = Encoding.UTF8.GetString(ea.Body.ToArray()); Console.WriteLine($"{DateTime.Now}，队列{dlxQueueName}消费消息:{message}"); channel.BasicAck(ea.DeliveryTag, false); }; channel.BasicConsume(dlxQueueName, autoAck: false, consumer); } } }
执行代码：
向延时队列发送消息，监听死信队列，发送和收到消息时间刚好是设置的10s。
RabbitMQ管理界面：
上面的延时队列能解决消息过期时间都是相同的场景，能不能解决消息的过期时间是不一样的呢？
例如场景：机器人客服，为了更像人为操作，收到消息后要随机3-10秒回复客户。
1）队列不设置TTL（消息过期时间），把过期时间设置在消息上。
生产者代码：
public static void SendMessage() { //死信交换机 string dlxexChange = "dlx.exchange"; //死信队列 string dlxQueueName = "dlx.queue"; //消息交换机 string exchange = "direct-exchange"; //消息队列 string queueName = "delay_queue"; using (var connection = RabbitMQHelper.GetConnection()) { using (var channel = connection.CreateModel()) { //创建死信交换机 channel.ExchangeDeclare(dlxexChange, type: ExchangeType.Direct, durable: true, autoDelete: false); //创建死信队列 channel.QueueDeclare(dlxQueueName, durable: true, exclusive: false, autoDelete: false); //死信队列绑定死信交换机 channel.QueueBind(dlxQueueName, dlxexChange, routingKey: dlxQueueName); // 创建消息交换机 channel.ExchangeDeclare(exchange, type: ExchangeType.Direct, durable: true, autoDelete: false); //创建消息队列,并指定死信队列，和设置这个队列的消息过期时间为10s channel.QueueDeclare(queueName, durable: true, exclusive: false, autoDelete: false, arguments: new Dictionary<string, object> { { "x-dead-letter-exchange",dlxexChange}, //设置当前队列的DLX(死信交换机) { "x-dead-letter-routing-key",dlxQueueName}, //设置DLX的路由key，DLX会根据该值去找到死信消息存放的队列 //{ "x-message-ttl",10000} //设置队列的消息过期时间 }); //消息队列绑定消息交换机 channel.QueueBind(queueName, exchange, routingKey: queueName); string message = "hello rabbitmq message 10s后处理"; var properties = channel.CreateBasicProperties(); properties.Persistent = true; properties.Expiration = "10000";//消息的有效期10s //发布消息,延时10s channel.BasicPublish(exchange: exchange, routingKey: queueName, basicProperties: properties, body: Encoding.UTF8.GetBytes(message)); Console.WriteLine($"{DateTime.Now},向队列:{queueName}发送消息:{message},延时:10s"); string message2 = "hello rabbitmq message 5s后处理"; var properties2 = channel.CreateBasicProperties(); properties2.Persistent = true; properties2.Expiration = "5000";//消息有效期5s //发布消息,延时5s channel.BasicPublish(exchange: exchange, routingKey: queueName, basicProperties: properties2, body: Encoding.UTF8.GetBytes(message2)); Console.WriteLine($"{DateTime.Now},向队列:{queueName}发送消息:{message2},延时:5s"); } } }
消费者代码还是上面延时队列的不变，先试下效果。
