C# 操作rabbitmq（三）

此篇介绍rabbitmq的Routing

一、使用exchange时，会广播给所有连接的consumer，而有时候我们需要订阅消息的子集就好，例如只需要其中的一些错误信息写入到日志当中

二、Bindings
在上一篇中我们创建了exchange和queue的绑定，其中有一个属性routingKey，该属性依赖于exchange的类型，fanout会忽略改属性。
direct类型的exchange可以实现这种需求

上图中，设置了orange为routingKey的exchange会被路由到Q1，设置了black或green的routingKey会被路由到Q2，其他未设置的会被放弃掉

三、Multiple bindings

绑定多个queue到同一个routingKey中是合法的，相当于fanout类型的exchange，会广播到绑定的响应queue中

四、例子

Publish

using System;
using System.Linq;
using RabbitMQ.Client;
using System.Text;

class EmitLogDirect
{
    public static void Main(string[] args)
    {
        var factory = new ConnectionFactory() { HostName = "localhost" };
        using(var connection = factory.CreateConnection())
        using(var channel = connection.CreateModel())
        {
            channel.ExchangeDeclare(exchange: "direct_logs",
                                    type: "direct");

            var severity = (args.Length > 0) ? args[0] : "info";
            var message = (args.Length > 1)
                          ? string.Join(" ", args.Skip( 1 ).ToArray())
                          : "Hello World!";
            var body = Encoding.UTF8.GetBytes(message);
            channel.BasicPublish(exchange: "direct_logs",
                                 routingKey: severity,
                                 basicProperties: null,
                                 body: body);
            Console.WriteLine(" [x] Sent '{0}':'{1}'", severity, message);
        }

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

Subscribe

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

class ReceiveLogsDirect
{
    public static void Main(string[] args)
    {
        var factory = new ConnectionFactory() { HostName = "localhost" };
        using(var connection = factory.CreateConnection())
        using(var channel = connection.CreateModel())
        {
            channel.ExchangeDeclare(exchange: "direct_logs",
                                    type: "direct");
            var queueName = channel.QueueDeclare().QueueName;

            if(args.Length < 1)
            {
                Console.Error.WriteLine("Usage: {0} [info] [warning] [error]",
                                        Environment.GetCommandLineArgs()[0]);
                Console.WriteLine(" Press [enter] to exit.");
                Console.ReadLine();
                Environment.ExitCode = 1;
                return;
            }

            foreach(var severity in args)
            {
                channel.QueueBind(queue: queueName,
                                  exchange: "direct_logs",
                                  routingKey: severity);
            }

            Console.WriteLine(" [*] Waiting for messages.");

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

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