RabbitMQ 设置消息的优先级

在RabbitMQ中，可以设置消息的优先级，也就相当于在队列中置顶某条消息，让某个消息优先得到处理的功能。

既然是设置消息的优先级，那么就是针对生产者，也就是消息发布端。

设置消息的优先级一共有2个步骤：

1、设置队列的x-max-priority参数；

2、设置消息的Priority参数。

话不多说，上代码！

发送端：

            var factory = new ConnectionFactory() { HostName = "localhost",UserName="ty2017",Password="123456",VirtualHost="log" };
            using (var connection = factory.CreateConnection()) {
                using (var channel = connection.CreateModel()) {   
                    //声明一个队列，设置x-max-priority参数
                    channel.QueueDeclare("q.test", true, false, false, new Dictionary<string, object> { { "x-max-priority", 30 } });
                   
                    for (int i = 0; i < 6; i++) {
                        var body = Encoding.UTF8.GetBytes(string.Format("第{0}个消息",i+1));
                        var properties = channel.CreateBasicProperties();
                        properties.SetPersistent(true);
                        //设置消息的优先级
                        properties.Priority = (byte)((i == 3)?30:i);  
                        //发布消息
                        channel.BasicPublish(exchange: "",
                                             routingKey: "q.test",
                                             basicProperties: properties,
                                             body: body);                       
                    }

                }
            }

将第四个消息的优先级设置为最大，我们打开Consumer端，看看第四个消息是否被优先处理！

Consumer端代码如下：

            var factory = new ConnectionFactory() { HostName = "localhost", UserName = "ty2017", Password = "123456",VirtualHost="log" };
            using (var connection = factory.CreateConnection()) {
                using (var channel = connection.CreateModel()) {                  
                    channel.QueueDeclare("q.test", true, false, false, new Dictionary<string, object> { { "x-max-priority", 30 } });                   

                    channel.BasicQos(0, 1, false);

                    var consumer = new EventingBasicConsumer(channel);
                    consumer.Received += (model, ea) => {
                        var body = ea.Body;
                        
                        var message = Encoding.UTF8.GetString(body);
                        Console.WriteLine("优先级:{0}  消息内容:{1}",ea.BasicProperties.Priority, message);  
                        channel.BasicAck(ea.DeliveryTag, false);

                    };
                    channel.BasicConsume(queue: "q.test",
                                         noAck: false,
                                         consumer: consumer);                  
                    Console.ReadLine();
                }
            }

运行Consumer端程序，得到如下结果：

根据结果可以看出，优先级越大的消息越是被优先处理！