RabbitMQ学习之Topics(5)

 上一节，我们讲了direct exchange，这节我们讲下topic exchange

Topic exchange

发送到topic exchange的messages不可以有一个随意的routing_key, 它必须是使用.分隔的一些词的集合。例如： "stock.usd.nyse", "nyse.vmw", "quick.orange.rabbit" .

这些binding key 必须有同样的样式(in the same form). topic exchange背后的逻辑与direct exchange相似：带有特定的routing key的message会发送到所有有匹配的binding key 的所有queues。

然而，对于binding keys有两个重要的特例：

• *（star） 能替代一个词

• #（hash） 能替代0个或者多个词

下面是一个简单的例子

这个例子中，我们将会发送描述动物的message. 这些message将会带有一个routing key . 这个routing key 由三个词组成. 第一个词描述速度(speed),第二个词描述肤色(colour)，第三个词描述物种。 <speed>.<colour>.<species>

我们创建了3条bindings. Q1 绑定”*.orange.*”并且Q2绑定“*.*.rabbit”和“lazy.#”

这些bindings总结下就是：

• Q1对所有的orange的动物感兴趣
• Q2想要了解所有的rabbit,和所有的lazy的动物

Topic exchange

Topic exchange是很强大的，并且可以表现的像其他exchange.

当一个queue绑定带“#”的binding key时，它可以接受所有的messages而不用管routing key.就像fanout exchange.

当特殊字符* 和#没有在bindings中使用时，topic exchange表现的像direct exchange. 

代码

我们将使用topic exchange.对于routing key ，我们将使用这两个词：<facility>.<severity>.

EmitLogTopic.cs

using System;using System.Linq;using RabbitMQ.Client;using System.Text;
class EmitLogTopic
{
    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: "topic_logs",  //topic类型的exchange
                                    type: "topic");

            var routingKey = (args.Length > 0) ? args[0] : "anonymous.info";
            var message = (args.Length > 1)
                          ? string.Join(" ", args.Skip( 1 ).ToArray())
                          : "Hello World!";
            var body = Encoding.UTF8.GetBytes(message);
            channel.BasicPublish(exchange: "topic_logs",  //发送特定routing key的message
                                 routingKey: routingKey,
                                 basicProperties: null,
                                 body: body);
            Console.WriteLine(" [x] Sent '{0}':'{1}'", routingKey, message);
        }
    }
}

使用示例：

cd EmitLogTopic
dotnet run "kern.critical" "A critical kernel error"

ReceiveLogsTopic.cs

using System;using RabbitMQ.Client;using RabbitMQ.Client.Events;using System.Text;
class ReceiveLogsTopic
{
    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: "topic_logs", type: "topic"); //声明topic exchange
            var queueName = channel.QueueDeclare().QueueName; //声明随机生成的queue name

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

            foreach(var bindingKey in args)
            {
                channel.QueueBind(queue: queueName,  //绑定bindingkey
                                  exchange: "topic_logs",
                                  routingKey: bindingKey);
            }

            Console.WriteLine(" [*] Waiting for messages. To exit press CTRL+C");

            var consumer = new EventingBasicConsumer(channel);
            consumer.Received += (model, ea) =>
            {
                var body = ea.Body;
                var message = Encoding.UTF8.GetString(body);
                var routingKey = ea.RoutingKey; //message的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();
        }
    }
}

使用示例：

接收所有的logs

cd ReceiveLogsTopic
dotnet run "#"

接收所有facility:kern的logs

cd ReceiveLogsTopic
dotnet run "kern.*"

仅仅critical的logs

cd ReceiveLogsTopic
dotnet run "*.critical"

创建多个bindings

cd ReceiveLogsTopic
dotnet run "kern.*" "*.critical"

参考网址：

https://www.rabbitmq.com/tutorials/tutorial-five-dotnet.html