在上一篇文章中，我們知道了RabbitMQ的訊息流程如下：

但在具體的使用中，我們還需知道exchange的型別，因為不同的型別對應不同的佇列和路由規則。

在rabbitmq中，exchange有4個型別：direct，topic，fanout，header。

direct exchange

此型別的exchange路由規則很簡單：

exchange在和queue進行binding時會設定routingkey

channel.QueueBind(queue: "create_pdf_queue",
                    exchange: "pdf_events",
                    routingKey: "pdf_create",
                    arguments: null);

 然後我們在將訊息傳送到exchange時會設定對應的routingkey：

channel.BasicPublish(exchange: "pdf_events",
                        routingKey: "pdf_create",
                        basicProperties: properties,
                        body: body);

 在direct型別的exchange中，只有這兩個routingkey完全相同，exchange才會選擇對應的binging進行訊息路由。

具體的流程如下：

通過程式碼可以會理解好一點：

var factory = new ConnectionFactory() { HostName = "localhost" };
using (var connection = factory.CreateConnection())
using (var channel = connection.CreateModel())
{
    // Direct型別的exchange, 名稱 pdf_events
    channel.ExchangeDeclare(exchange: "pdf_events",
                            type: ExchangeType.Direct,
                            durable: true,
                            autoDelete: false,
                            arguments: null);

    // 建立create_pdf_queue佇列
    channel.QueueDeclare(queue: "create_pdf_queue",
                            durable: true,
                            exclusive: false,
                            autoDelete: false,
                            arguments: null);

    //建立 pdf_log_queue佇列
    channel.QueueDeclare(queue: "pdf_log_queue",
                            durable: true,
                            exclusive: false,
                            autoDelete: false,
                            arguments: null);

    //繫結 pdf_events --> create_pdf_queue 使用routingkey:pdf_create
    channel.QueueBind(queue: "create_pdf_queue",
                        exchange: "pdf_events",
                        routingKey: "pdf_create",
                        arguments: null);

    //繫結 pdf_events --> pdf_log_queue 使用routingkey:pdf_log
    channel.QueueBind(queue: "pdf_log_queue",
                        exchange: "pdf_events",
                        routingKey: "pdf_log",
                        arguments: null);


    var message = "Demo some pdf creating...";
    var body = Encoding.UTF8.GetBytes(message);
    var properties = channel.CreateBasicProperties();
    properties.Persistent = true;

    //傳送訊息到exchange :pdf_events ,使用routingkey: pdf_create
    //通過binding routinekey的比較，次訊息會路由到佇列 create_pdf_queue
    channel.BasicPublish(exchange: "pdf_events",
                routingKey: "pdf_create",
                basicProperties: properties,
                body: body);

    message = "pdf loging ...";
    body = Encoding.UTF8.GetBytes(message);
    properties = channel.CreateBasicProperties();
    properties.Persistent = true;

    //傳送訊息到exchange :pdf_events ,使用routingkey: pdf_log
    //通過binding routinekey的比較，次訊息會路由到佇列 pdf_log_queue
    channel.BasicPublish(exchange: "pdf_events",
            routingKey: "pdf_log",
            basicProperties: properties,
            body: body);

    
}

 topic exchange

此型別exchange和上面的direct型別差不多，但direct型別要求routingkey完全相等，這裡的routingkey可以有萬用字元：'*','#'.

其中'*'表示匹配一個單詞， '#'則表示匹配沒有或者多個單詞

如上圖第一個binding：

• exchange: agreements
• queue A:  berlin_agreements
• binding routingkey: agreements.eu.berlin.#

第二個binding: 

• exchange: agreements
• queue B: all_agreements
• binding routingkey: agreements.#

第三個binding：

• exchange: agreements
• queue c: headstore_agreements
• binding routingkey: agreements.eu.*.headstore

所以如果我們訊息的routingkey為agreements.eu.berlin那麼符合第一和第二個binding，但最後一個不符合，具體的程式碼如下：

var factory = new ConnectionFactory() { HostName = "localhost" };
using (var connection = factory.CreateConnection())
using (var channel = connection.CreateModel())
{
    // Topic型別的exchange, 名稱 agreements
    channel.ExchangeDeclare(exchange: "agreements",
                            type: ExchangeType.Topic,
                            durable: true,
                            autoDelete: false,
                            arguments: null);

    // 建立berlin_agreements佇列
    channel.QueueDeclare(queue: "berlin_agreements",
                            durable: true,
                            exclusive: false,
                            autoDelete: false,
                            arguments: null);

    //建立 all_agreements 佇列
    channel.QueueDeclare(queue: "all_agreements",
                            durable: true,
                            exclusive: false,
                            autoDelete: false,
                            arguments: null);

    //建立 headstore_agreements 佇列
    channel.QueueDeclare(queue: "headstore_agreements",
                            durable: true,
                            exclusive: false,
                            autoDelete: false,
                            arguments: null);

    //繫結 agreements --> berlin_agreements 使用routingkey:agreements.eu.berlin.#
    channel.QueueBind(queue: "berlin_agreements",
                        exchange: "agreements",
                        routingKey: "agreements.eu.berlin.#",
                        arguments: null);

    //繫結 agreements --> all_agreements 使用routingkey:agreements.#
    channel.QueueBind(queue: "all_agreements",
                        exchange: "agreements",
                        routingKey: "agreements.#",
                        arguments: null);

    //繫結 agreements --> headstore_agreements 使用routingkey:agreements.eu.*.headstore
    channel.QueueBind(queue: "headstore_agreements",
                        exchange: "agreements",
                        routingKey: "agreements.eu.*.headstore",
                        arguments: null);


    var message = "hello world";
    var body = Encoding.UTF8.GetBytes(message);
    var properties = channel.CreateBasicProperties();
    properties.Persistent = true;

    //傳送訊息到exchange :agreements ,使用routingkey: agreements.eu.berlin
    //agreements.eu.berlin 匹配  agreements.eu.berlin.# 和agreements.#
    //agreements.eu.berlin 不匹配  agreements.eu.*.headstore
    //最終次訊息會路由到隊裡：berlin_agreements（agreements.eu.berlin.#） 和 all_agreements（agreements.#）
    channel.BasicPublish(exchange: "agreements",
                            routingKey: "agreements.eu.berlin",
                            basicProperties: properties,
                            body: body);

               
}

 fanout exchange

此exchange的路由規則很簡單直接將訊息路由到所有繫結的佇列中，無須對訊息的routingkey進行匹配操作。

header exchange

 此型別的exchange和以上三個都不一樣，其路由的規則是根據header來判斷，其中的header就是以下方法的arguments引數：

Dictionary<string, object> aHeader = new Dictionary<string, object>();
aHeader.Add("format", "pdf");
aHeader.Add("type", "report");
aHeader.Add("x-match", "all");
channel.QueueBind(queue: "queue.A",
                    exchange: "agreements",
                    routingKey: string.Empty,
                    arguments: aHeader);

其中的x-match為特殊的header，可以為all則表示要匹配所有的header，如果為any則表示只要匹配其中的一個header即可。

在釋出訊息的時候就需要傳入header值：

var properties = channel.CreateBasicProperties();
properties.Persistent = true;
Dictionary<string, object> mHeader1 = new Dictionary<string, object>();
mHeader1.Add("format", "pdf");
mHeader1.Add("type", "report");
properties.Headers = mHeader1;

 具體的規則可以看以下程式碼：

var factory = new ConnectionFactory() { HostName = "localhost" };
using (var connection = factory.CreateConnection())
using (var channel = connection.CreateModel())
{
    // Headers型別的exchange, 名稱 agreements
    channel.ExchangeDeclare(exchange: "agreements",
                            type: ExchangeType.Headers,
                            durable: true,
                            autoDelete: false,
                            arguments: null);

    // 建立queue.A佇列
    channel.QueueDeclare(queue: "queue.A", durable: true, exclusive: false, autoDelete: false, arguments: null);

    //建立 queue.B 佇列
    channel.QueueDeclare(queue: "queue.B", durable: true, exclusive: false, autoDelete: false, arguments: null);

    //建立 queue.C 佇列
    channel.QueueDeclare(queue: "queue.C", durable: true, exclusive: false, autoDelete: false, arguments: null);

    //繫結 agreements --> queue.A 使用arguments (format=pdf, type=report, x-match=all)
    Dictionary<string, object> aHeader = new Dictionary<string, object>();
    aHeader.Add("format", "pdf");
    aHeader.Add("type", "report");
    aHeader.Add("x-match", "all");
    channel.QueueBind(queue: "queue.A",
                        exchange: "agreements",
                        routingKey: string.Empty,
                        arguments: aHeader);

    //繫結 agreements --> queue.B 使用arguments (format=pdf, type=log, x-match=any)
    Dictionary<string, object> bHeader = new Dictionary<string, object>();
    bHeader.Add("format", "pdf");
    bHeader.Add("type", "log");
    bHeader.Add("x-match", "any");
    channel.QueueBind(queue: "queue.B",
                        exchange: "agreements",
                        routingKey: string.Empty,
                        arguments: bHeader);

    //繫結 agreements --> queue.C 使用arguments (format=zip, type=report, x-match=all)
    Dictionary<string, object> cHeader = new Dictionary<string, object>();
    cHeader.Add("format", "zip");
    cHeader.Add("type", "report");
    cHeader.Add("x-match", "all");
    channel.QueueBind(queue: "queue.C",
                        exchange: "agreements",
                        routingKey: string.Empty,
                        arguments: cHeader);


    string message1 = "hello world";
    var body = Encoding.UTF8.GetBytes(message1);
    var properties = channel.CreateBasicProperties();
    properties.Persistent = true;
    Dictionary<string, object> mHeader1 = new Dictionary<string, object>();
    mHeader1.Add("format", "pdf");
    mHeader1.Add("type", "report");
    properties.Headers = mHeader1;
    //此訊息路由到 queue.A 和 queue.B
    //queue.A 的binding (format=pdf, type=report, x-match=all)
    //queue.B 的binding (format = pdf, type = log, x - match = any)
    channel.BasicPublish(exchange: "agreements",
                            routingKey: string.Empty,
                            basicProperties: properties,
                            body: body);


    string message2 = "hello world";
    body = Encoding.UTF8.GetBytes(message2);
    properties = channel.CreateBasicProperties();
    properties.Persistent = true;
    Dictionary<string, object> mHeader2 = new Dictionary<string, object>();
    mHeader2.Add("type", "log");
    properties.Headers = mHeader2;
    //x-match 配置queue.B 
    //queue.B 的binding (format = pdf, type = log, x-match = any)
    channel.BasicPublish(exchange: "agreements",
                    routingKey: string.Empty,
                    basicProperties: properties,
                    body: body);

    string message3= "hello world";
    body = Encoding.UTF8.GetBytes(message3);
    properties = channel.CreateBasicProperties();
    properties.Persistent = true;
    Dictionary<string, object> mHeader3 = new Dictionary<string, object>();
    mHeader3.Add("format", "zip");
    properties.Headers = mHeader3;
    //配置失敗，不會被路由
    channel.BasicPublish(exchange: "agreements",
                    routingKey: string.Empty,
                    basicProperties: properties,
                    body: body);


}

 總計

以上就是exchange 型別的總結，一般來說direct和topic用來具體的路由訊息，如果要用廣播的訊息一般用fanout的exchange。

header型別用的比較少，但還是知道一點好。