RabbitMQ消息隊列（八）-通過Topic主題模式分發消息（.Net Core版）

前兩章我們講了RabbitMQ的direct模式和fanout模式，本章介紹topic主題模式的應用。如果對direct模式下通過routingkey來匹配消息的模式已經有一定了解那fanout也很好理解。簡單的可以理解成direct是通過routingkey精准匹配的，而topic是通過routingkey來模糊匹配。 
在topic模式下支持兩個特殊字符的匹配。

* (星號) 代表任意 一個單詞
# (井號) 0個或者多個單詞

注意：上面說的是單詞不是字符。

如下圖所示，RabbitMQ direct模式通過RoutingKey來精准匹配，RoutingKey為red的投遞到Queue1，RoutingKey為black和white的投遞到Queue2。 

我們可以假設一個場景，我們要做一個日志模塊來收集處理不同的日志，日志區分包含三個維度的標准：模塊、日志緊急程度、日志重要程度。模塊分為：red、black、white；緊急程度分為：critical、normal；把重要程度分為：medium、low、high在RoutingKey字段中我們把這三個維度通過兩個“.“連接起來。 
現在我們需要對black模塊，緊急程度為critical，重要程度為high的日志分配到隊列1打印到屏幕；對所以模塊重要程度為high的日志和white緊急程度為critical的日志發送到隊列2持久化到硬盤。如下示例：

• RoutingKey為“black.critical.high”的日志會投遞到queue1和queue2,。

• RoutingKey為“red.critical.high”的日志會只投遞到queue2。

• RoutingKey為“white.critical.high”的日志會投遞到queue2，並且雖然queue2的兩個匹配規則都符合但只會向queue2投遞一份。

 新建TopicProduct用來發布三種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接收一種消息

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接收兩種消息

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();
                }
            }
        }
    }
}

先運行TopicCustomerA和TopicCustomerB保持訂閱狀態。然后執行TopicProduct發布消息。TopicCustomerA和TopicCustomerB收到的消息如下：

如上截圖，驗證了我們之前的結論。

另外還有一些特殊情況例如：

如果binding_key 是 “#” - 它會接收所有的Message，不管routing_key是什么，就像是fanout 
exchange。
如果 “*” and “#” 沒有被使用，那么topic exchange就變成了direct exchange。