RabbitMQ消息队列（八）-通过Topic主题模式分发消息（.Net Core版）

前两章我们讲了RabbitMQ的direct模式和fanout模式，本章介绍topic主题模式的应用。如果对direct模式下通过routingkey来匹配消息的模式已经有一定了解那fanout也很好理解。简单的可以理解成direct是通过routingkey精准匹配的，而topic是通过routingkey来模糊匹配。 
在topic模式下支持两个特殊字符的匹配。

* (星号) 代表任意 一个单词
# (井号) 0个或者多个单词

注意：上面说的是单词不是字符。

如下图所示，RabbitMQ direct模式通过RoutingKey来精准匹配，RoutingKey为red的投递到Queue1，RoutingKey为black和white的投递到Queue2。 

我们可以假设一个场景，我们要做一个日志模块来收集处理不同的日志，日志区分包含三个维度的标准：模块、日志紧急程度、日志重要程度。模块分为：red、black、white；紧急程度分为：critical、normal；把重要程度分为：medium、low、high在RoutingKey字段中我们把这三个维度通过两个“.“连接起来。 
现在我们需要对black模块，紧急程度为critical，重要程度为high的日志分配到队列1打印到屏幕；对所以模块重要程度为high的日志和white紧急程度为critical的日志发送到队列2持久化到硬盘。如下示例：

• RoutingKey为“black.critical.high”的日志会投递到queue1和queue2,。

• RoutingKey为“red.critical.high”的日志会只投递到queue2。

• RoutingKey为“white.critical.high”的日志会投递到queue2，并且虽然queue2的两个匹配规则都符合但只会向queue2投递一份。

 新建TopicProduct用来发布三种routingkey的消息。

using System;
using System.Text;
using RabbitMQ.Client;
using RabbitMQ.Client.Events;

namespace TopicProduct
{
    class Program
    {
        static void Main(string[] args)
        {
            String exchangeName = "wytExchangeTopic";
            String routeKeyName1 = "black.critical.high";
            String routeKeyName2 = "red.critical.high";
            String routeKeyName3 = "white.critical.high";
            
            String message1 = "black-critical-high!";
            String message2 = "red-critical-high!";
            String message3 = "white-critical-high!";

            ConnectionFactory factory = new ConnectionFactory();
            factory.HostName = "192.168.63.129";
            factory.Port = 5672;
            factory.VirtualHost = "/wyt";
            factory.UserName = "wyt";
            factory.Password = "wyt";

            using (IConnection connection=factory.CreateConnection())
            {
                using (IModel channel=connection.CreateModel())
                {
                    channel.ExchangeDeclare(exchange: exchangeName, type: "topic", durable: true, autoDelete: false, arguments: null);

                    IBasicProperties properties = channel.CreateBasicProperties();
                    properties.Persistent = true;

                    Byte[] body1 = Encoding.UTF8.GetBytes(message1);
                    Byte[] body2 = Encoding.UTF8.GetBytes(message2);
                    Byte[] body3 = Encoding.UTF8.GetBytes(message3);

                    //消息推送
                    channel.BasicPublish(exchange: exchangeName, routingKey:routeKeyName1,basicProperties: properties, body: body1);
                    channel.BasicPublish(exchange: exchangeName, routingKey: routeKeyName2, basicProperties: properties, body: body2);
                    channel.BasicPublish(exchange: exchangeName, routingKey: routeKeyName3, basicProperties: properties, body: body3);

                    Console.WriteLine(" [x] Sent {0}", message1);
                    Console.WriteLine(" [x] Sent {0}", message2);
                    Console.WriteLine(" [x] Sent {0}", message3);
                }
            }

            Console.WriteLine(" Press [enter] to exit.");
            Console.ReadLine();
        }
    }
}

新建TopicCustomerA接收一种消息

using System;
using System.Text;
using RabbitMQ.Client;
using RabbitMQ.Client.Events;

namespace TopicCustomerA
{
    class Program
    {
        static void Main(string[] args)
        {
            String exchangeName = "wytExchangeTopic";
            String routeKeyName1 = "black.critical.high";

            ConnectionFactory factory = new ConnectionFactory();
            factory.HostName = "192.168.63.129";
            factory.Port = 5672;
            factory.VirtualHost = "/wyt";
            factory.UserName = "wyt";
            factory.Password = "wyt";

            using (IConnection connection=factory.CreateConnection())
            {
                using (IModel channel=connection.CreateModel())
                {
                    channel.ExchangeDeclare(exchange: exchangeName, type: "topic", durable: true, autoDelete: false, arguments: null);

                    String queueName = channel.QueueDeclare().QueueName;

                    channel.QueueBind(queue: queueName, exchange: exchangeName, routingKey: routeKeyName1, arguments: null);

                    EventingBasicConsumer consumer = new EventingBasicConsumer(channel);
                    consumer.Received += (model, ea) =>
                    {
                        var body = ea.Body;
                        var message = Encoding.UTF8.GetString(body);
                        var routingKey = ea.RoutingKey;
                        Console.WriteLine(" [x] Received '{0}':'{1}'", routingKey, message);

                        channel.BasicAck(deliveryTag: ea.DeliveryTag, multiple: false);
                    };

                    channel.BasicConsume(queue: queueName, autoAck: false, consumer: consumer);

                    Console.WriteLine(" Press [enter] to exit.");
                    Console.ReadLine();
                }
            }
        }
    }
}

新建TopicCustomerB接收两种消息

using System;
using System.Text;
using RabbitMQ.Client;
using RabbitMQ.Client.Events;

namespace TopicCustomerB
{
    class Program
    {
        static void Main(string[] args)
        {
            String exchangeName = "wytExchangeTopic";
            String routeKeyName1 = "red.critical.*";
            String routeKeyName2 = "white.critical.*";

            ConnectionFactory factory = new ConnectionFactory();
            factory.HostName = "192.168.63.129";
            factory.Port = 5672;
            factory.VirtualHost = "/wyt";
            factory.UserName = "wyt";
            factory.Password = "wyt";

            using (IConnection connection = factory.CreateConnection())
            {
                using (IModel channel = connection.CreateModel())
                {
                    channel.ExchangeDeclare(exchange: exchangeName, type: "topic", durable: true, autoDelete: false, arguments: null);

                    String queueName = channel.QueueDeclare().QueueName;

                    channel.QueueBind(queue: queueName, exchange: exchangeName, routingKey: routeKeyName1, arguments: null);
                    channel.QueueBind(queue: queueName, exchange: exchangeName, routingKey: routeKeyName2, arguments: null);

                    EventingBasicConsumer consumer = new EventingBasicConsumer(channel);
                    consumer.Received += (model, ea) =>
                    {
                        var body = ea.Body;
                        var message = Encoding.UTF8.GetString(body);
                        var routingKey = ea.RoutingKey;
                        Console.WriteLine(" [x] Received '{0}':'{1}'", routingKey, message);

                        channel.BasicAck(deliveryTag: ea.DeliveryTag, multiple: false);
                    };

                    channel.BasicConsume(queue: queueName, autoAck: false, consumer: consumer);

                    Console.WriteLine(" Press [enter] to exit.");
                    Console.ReadLine();
                }
            }
        }
    }
}

先运行TopicCustomerA和TopicCustomerB保持订阅状态。然后执行TopicProduct发布消息。TopicCustomerA和TopicCustomerB收到的消息如下：

如上截图，验证了我们之前的结论。

另外还有一些特殊情况例如：

如果binding_key 是 “#” - 它会接收所有的Message，不管routing_key是什么，就像是fanout 
exchange。
如果 “*” and “#” 没有被使用，那么topic exchange就变成了direct exchange。