RabbitMQ消息队列（九）-通过Headers模式分发消息（.Net Core版）

Headers类型的exchange使用的比较少，以至于官方文档貌似都没提到，它是忽略routingKey的一种路由方式。是使用Headers来匹配的。Headers是一个键值对，可以定义成Hashtable。发送者在发送的时候定义一些键值对，接收者也可以再绑定时候传入一些键值对，两者匹配的话，则对应的队列就可以收到消息。 

匹配有两种方式all和any。这两种方式是在接收端必须要用键值”x-mactch”来定义。all代表定义的多个键值对都要满足，any代表只要满足一个就可以。fanout，direct，topic exchange的routingKey都需要要字符串形式的，而headers exchange则没有这个要求，因为键值对的值可以是任何类型。 

那在.Net Core中怎么应用呢？ 

headers也是一种交换机类型，但是在rabbitmq官网中的教程中并没有说到。资料也很少，但是找一找总会有的。

headers与direct的模式不同，不是使用routingkey去做绑定。而是通过消息headers的键值对匹配

发布者  -- >  headersexchange  -->  (user:  “小明 ”) binding  --> queue

也就是说 user: 小明 替代了之前的routingkey。在做绑定的时候有两种匹配方式供选择。x-match (all/any)

意思就是键值对中所有的项都要匹配与只要有一个匹配就可以。下面就可以动手写代码了

新建HeadersProduct用来发布新消息：

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

namespace HeadersProduct
{
    class Program
    {
        static void Main(string[] args)
        {
            String exchangeName = "wytExchangeHeaders";

            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: "headers", durable: true, autoDelete: false, arguments: null);

                    IBasicProperties properties = channel.CreateBasicProperties();
                    properties.Headers = new Dictionary<String, Object>()
                    {
                        {"user","wyt" },
                        {"password","wyt"}
                    };

                    Byte[] body = Encoding.UTF8.GetBytes("Hello World");

                    channel.BasicPublish(exchange: exchangeName, routingKey: String.Empty, basicProperties: properties, body: body);
                }
            }

            Console.Write("发布成功！");

            Console.ReadKey();
        }
    }
}

新建HeadersConsumerA来以正确的headers接收消息：

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

namespace HeadersConsumerA
{
    class Program
    {
        static void Main(string[] args)
        {



            String exchangeName = "wytExchangeHeaders";

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

            bool flag = true;
            string pattern = "";
            while (flag)
            {
                Console.WriteLine("请选择headers匹配模式  1(any)/2(all)");
                pattern = Console.ReadLine();
                if (pattern == "1" || pattern == "2")
                    flag = false;
                else
                    Console.Write("请做出正确的选择");
            }
            //根据声明使用的队列
            var headersType = pattern == "1" ? "any" : "all";

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

                    String queueName = channel.QueueDeclare().QueueName;

                    channel.QueueBind(queue: queueName, exchange: exchangeName, routingKey: String.Empty, arguments: new Dictionary<String, Object>
                    {
                        {"x-math",headersType },
                        {"user","wyt" },
                        {"password","wyt" }
                    });

                    EventingBasicConsumer consumer = new EventingBasicConsumer(channel);
                    consumer.Received += (model, ea) =>
                    {
                        var msg = Encoding.UTF8.GetString(ea.Body);

                        Console.WriteLine($"{msg}");
                    };

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


                    Console.ReadKey();

                }
            }
        }
    }
}

新建HeadersConsumerB来以错误的headers接收消息：

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

namespace HeadersConsumerB
{
    class Program
    {
        static void Main(string[] args)
        {
            String exchangeName = "wytExchangeHeaders";

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

            bool flag = true;
            string pattern = "";
            while (flag)
            {
                Console.WriteLine("请选择headers匹配模式  1(any)/2(all)");
                pattern = Console.ReadLine();
                if (pattern == "1" || pattern == "2")
                    flag = false;
                else
                    Console.Write("请做出正确的选择");
            }
            //根据声明使用的队列
            var headersType = pattern == "1" ? "any" : "all";

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

                    String queueName = channel.QueueDeclare().QueueName;

                    channel.QueueBind(queue: queueName, exchange: exchangeName, routingKey: String.Empty, arguments: new Dictionary<String, Object>
                    {
                        {"x-math",headersType },
                        {"user","xxx" },
                        {"password","xxx" }
                    });

                    EventingBasicConsumer consumer = new EventingBasicConsumer(channel);
                    consumer.Received += (model, ea) =>
                    {
                        var msg = Encoding.UTF8.GetString(ea.Body);

                        Console.WriteLine($"{msg}");
                    };

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


                    Console.ReadKey();

                }
            }

        }
    }
}

运行结果

一个可以接收到消息，另一个由于headers是不匹配的，所有接收不到消息