RabbitMq中的交換機

      Rabbitmq的核心概念（如下圖所示）：有虛擬主機、交換機、隊列、綁定；

      

     

      交換機可以理解成具有路由表的路由程序，僅此而已。每個消息都有一個稱為路由鍵（routing key）的屬性，就是一個簡單的字符串。

      最新版本的RabbitMQ有四種交換機類型，分別是Direct exchange、Fanout exchange、Topic exchange、Headers exchange。

      Direct Exchange – 處理路由鍵。需要將一個隊列綁定到交換機上，要求該消息與一個特定的路由鍵完全匹配。這是一個完整的匹配。如果一個隊列綁定到該交換機上要求路由鍵 “dog”，則只有被標記為“dog”的消息才被轉發，不會轉發dog.puppy，也不會轉發dog.guard，只會轉發dog。

      

     Fanout Exchange – 不處理路由鍵。你只需要簡單的將隊列綁定到交換機上。一個發送到交換機的消息都會被轉發到與該交換機綁定的所有隊列上。很像子網廣播，每台子網內的主機都獲得了一份復制的消息。Fanout交換機轉發消息是最快的。

      

 

      Topic Exchange – 將路由鍵和某模式進行匹配。此時隊列需要綁定要一個模式上。符號“#”匹配一個或多個詞，符號“*”匹配不多不少一個詞。因此“audit.#”能夠匹配到“audit.irs.corporate”，但是“audit.*” 只會匹配到“audit.irs”。

      

      

      Headers exchange – 還沒有仔細研究過，復制點官方的介紹吧。

      A headers exchange is designed to for routing on multiple attributes that are more easily expressed as message headers than a routing key. Headers exchanges ignore the routing key attribute. Instead, the attributes used for routing are taken from the headers attribute. A message is considered matching if the value of the header equals the value specified upon binding.

      It is possible to bind a queue to a headers exchange using more than one header for matching. In this case, the broker needs one more piece of information from the application developer, namely, should it consider messages with any of the headers matching, or all of them? This is what the "x-match" binding argument is for. When the "x-match" argument is set to "any", just one matching header value is sufficient. Alternatively, setting "x-match" to "all" mandates that all the values must match.

      Headers exchanges can be looked upon as "direct exchanges on steroids". Because they route based on header values, they can be used as direct exchanges where the routing key does not have to be a string; it could be an integer or a hash (dictionary) for example.

      消息始終都是先發送到交換機，由交換級經過路由傳送給隊列，消費者再從隊列中獲取消息的！

 

      參考資料：http://melin.iteye.com/blog/691265