前面的例子中，盡管我們使用了direct路由代替fanout路由解決了盲目廣播的問題，但direct路由也有它的缺陷，他不能基于多個(gè)標(biāo)準(zhǔn)做路由轉(zhuǎn)發(fā)。

　　在上面的日志系統(tǒng)中，如果不僅想基于日志等級(jí)做訂閱，也想根據(jù)日志的發(fā)生源做訂閱該怎么處理呢？這時(shí)候你可能想到了unix系統(tǒng)工具中的syslog服務(wù)，它不僅基于日志等級(jí)（info/warn/crit...）進(jìn)行路由轉(zhuǎn)發(fā)，也會(huì)根據(jù)操作（auth/cron/kern...）做路由轉(zhuǎn)發(fā)。

　　如果是那樣的話，日志系統(tǒng)就靈活多了，它不僅能夠監(jiān)聽來自‘cron’的關(guān)鍵錯(cuò)誤，也能監(jiān)聽來自'kern'的所有日志。其實(shí)主題交換機(jī)（topic exchange）就能解決這種問題。

　　主題交換機(jī)（Topic exchange）

　　主題交換機(jī)的路由代碼不能是任意寫的，必須是小樹點(diǎn)分隔開的一組單詞列表。這些單詞可以隨便寫，但通常是與連接消息特征有關(guān)的單詞。有效地路由代碼應(yīng)該是這樣的“stock.usd.nyse”，“nyse.vmw”，“quick.orange.rabbit”。路由代碼可以隨便寫，但是長度限制在255字節(jié)。

　　注意，綁定代碼也必須在同一個(gè)表單中。topic交換機(jī)與direct交換機(jī)類似-具有特定路由代碼的消息會(huì)傳送給所有匹配綁定代碼的隊(duì)列，但有兩個(gè)特殊的綁定代碼：

　　* ：它能替代一個(gè)單詞　

　　#：它能替代0或多個(gè)單詞

　　該例子中，我們給所有的動(dòng)物發(fā)送消息，符合由三個(gè)單詞（第一個(gè)單詞描述速度；第二個(gè)單詞描述顏色；第三個(gè)單詞描述物種）組成的路由代碼將會(huì)發(fā)送消息:“<speed>.<colour>.<species>”。

? ?

　　我們創(chuàng)建了三個(gè)綁定：Q1使用“*.orange.*”綁定，Q2使用“*.*.rabbit”和“l(fā)azy.#”綁定。這些綁定的意義如下：

??

　　Q1描述了所有顏色為橙色的動(dòng)物。

??

　　Q2描述了是兔子的動(dòng)物和懶惰的動(dòng)物。

??

　　這樣，“quick.orange.rabbit”消息通過路由轉(zhuǎn)發(fā)給Q1、Q2兩個(gè)隊(duì)列。"lazy.orange.elephant"消息也會(huì)轉(zhuǎn)發(fā)給Q1、Q2兩個(gè)隊(duì)列。“quick.orange.fox”消息只會(huì)轉(zhuǎn)發(fā)給Q1隊(duì)列，"lazy.brown.fox"也只會(huì)轉(zhuǎn)發(fā)給Q2隊(duì)列。"lazy.pink.rabbit"會(huì)轉(zhuǎn)發(fā)給Q2隊(duì)列一次，盡管它匹配兩個(gè)綁定。"quick.brown.fox"并不匹配任何一個(gè)隊(duì)列就會(huì)被廢棄。

??

　　如果我們打破規(guī)則，每次只發(fā)一個(gè)或四個(gè)單詞的話，如“orange”或”quick.orange.male.rabbit“，這些消息不匹配任何綁定，就會(huì)被廢棄。但如果發(fā)送”lazy.orange.male.rabbit“這樣的消息的話，由于它匹配最后的綁定仍會(huì)被轉(zhuǎn)發(fā)到Q2隊(duì)列中。

? ??

　　主題交換機(jī)是一種非常強(qiáng)大的交換機(jī)，當(dāng)它只綁定”#“時(shí)，它會(huì)接收所有的消息，與fanout交換機(jī)類似。當(dāng)沒有使用”*“和”#“符號(hào)時(shí)，主題交換機(jī)的作用等同與direct交換機(jī)。

　　源代碼

EmitLogTopic.java

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package?com.favccxx.favrabbit; import?com.rabbitmq.client.Channel; import?com.rabbitmq.client.Connection; import?com.rabbitmq.client.ConnectionFactory; public?class?EmitLogTopic?{ ????private?static?final?String?EXCHANGE_NAME?=?"topic_logs"; ????public?static?void?main(String[]?argv)?{ ????????Connection?connection?=?null; ????????Channel?channel?=?null; ????????try?{ ????????????ConnectionFactory?factory?=?new?ConnectionFactory(); ????????????factory.setHost("localhost"); ????????????connection?=?factory.newConnection(); ????????????channel?=?connection.createChannel(); ????????????channel.exchangeDeclare(EXCHANGE_NAME,?"topic"); ????????????String[]?routingKeys?=?{?"fast.orange.duck",?"slow.orange.fish",?"grey.rabbit",?"fast.black.rabbit", ????????????????????"quick.white.rabbit",?"lazy.dog",?"lazy.black.pig"?}; ????????????String[]?messages?=?{?"Hello",?"Guys",?"Girls",?"Babies"?}; ????????????for?(int?i?=?0;?i?<?routingKeys.length;?i++)?{ ????????????????for?(int?j?=?0;?j?<?messages.length;?j++)?{ ????????????????????channel.basicPublish(EXCHANGE_NAME,?routingKeys[i],?null,?messages[j].getBytes("UTF-8")); ????????????????????System.out.println("?[x]?Sent?'"?+?routingKeys[i]?+?"':'"?+?messages[j]?+?"'"); ????????????????} ????????????} ????????}?catch?(Exception?e)?{ ????????????e.printStackTrace(); ????????}?finally?{ ????????????if?(connection?!=?null)?{ ????????????????try?{ ????????????????????connection.close(); ????????????????}?catch?(Exception?ignore)?{ ????????????????} ????????????} ????????} ????} }

ReceiveLogsTopic.java

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package?com.favccxx.favrabbit; import?java.io.IOException; import?com.rabbitmq.client.AMQP; import?com.rabbitmq.client.Channel; import?com.rabbitmq.client.Connection; import?com.rabbitmq.client.ConnectionFactory; import?com.rabbitmq.client.Consumer; import?com.rabbitmq.client.DefaultConsumer; import?com.rabbitmq.client.Envelope; public?class?ReceiveLogsTopic?{ ????private?static?final?String?EXCHANGE_NAME?=?"topic_logs"; ????public?static?void?main(String[]?argv)?throws?Exception?{ ????????ConnectionFactory?factory?=?new?ConnectionFactory(); ????????factory.setHost("localhost"); ????????Connection?connection?=?factory.newConnection(); ????????Channel?channel?=?connection.createChannel(); ????????channel.exchangeDeclare(EXCHANGE_NAME,?"topic"); ????????String?queueName?=?channel.queueDeclare().getQueue(); ????????String[]?bindingKeys?=?{?"*.orange.*",?"*.*.rabbit",?"lazy.#"?}; ????????for?(final?String?bindingKey?:?bindingKeys)?{ ????????????channel.queueBind(queueName,?EXCHANGE_NAME,?bindingKey); ????????????Consumer?consumer?=?new?DefaultConsumer(channel)?{ ????????????????@Override ????????????????public?void?handleDelivery(String?consumerTag,?Envelope?envelope,?AMQP.BasicProperties?properties, ????????????????????????byte[]?body)?throws?IOException?{ ????????????????????String?message?=?new?String(body,?"UTF-8"); ????????????????????System.out.println("["?+?bindingKey?+?"]?Received?message?:'"?+?message?+?"'?from?routingKey?:?"?+?envelope.getRoutingKey()); ????????????????} ????????????}; ????????????channel.basicConsume(queueName,?true,?consumer); ????????} ????} }

運(yùn)行消息發(fā)送器，在消息接收平臺(tái)輸出內(nèi)容如下

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[*.orange.*]?Received?message?:'Hello'?from?routingKey?:?fast.orange.duck [*.*.rabbit]?Received?message?:'Guys'?from?routingKey?:?fast.orange.duck [lazy.#]?Received?message?:'Girls'?from?routingKey?:?fast.orange.duck [*.orange.*]?Received?message?:'Babies'?from?routingKey?:?fast.orange.duck [*.*.rabbit]?Received?message?:'Hello'?from?routingKey?:?slow.orange.fish [lazy.#]?Received?message?:'Guys'?from?routingKey?:?slow.orange.fish [*.orange.*]?Received?message?:'Girls'?from?routingKey?:?slow.orange.fish [*.*.rabbit]?Received?message?:'Babies'?from?routingKey?:?slow.orange.fish [lazy.#]?Received?message?:'Hello'?from?routingKey?:?fast.black.rabbit [*.orange.*]?Received?message?:'Guys'?from?routingKey?:?fast.black.rabbit [*.*.rabbit]?Received?message?:'Girls'?from?routingKey?:?fast.black.rabbit [lazy.#]?Received?message?:'Babies'?from?routingKey?:?fast.black.rabbit [*.orange.*]?Received?message?:'Hello'?from?routingKey?:?quick.white.rabbit [*.*.rabbit]?Received?message?:'Guys'?from?routingKey?:?quick.white.rabbit [lazy.#]?Received?message?:'Girls'?from?routingKey?:?quick.white.rabbit [*.orange.*]?Received?message?:'Babies'?from?routingKey?:?quick.white.rabbit [*.*.rabbit]?Received?message?:'Hello'?from?routingKey?:?lazy.dog [lazy.#]?Received?message?:'Guys'?from?routingKey?:?lazy.dog [*.orange.*]?Received?message?:'Girls'?from?routingKey?:?lazy.dog [*.*.rabbit]?Received?message?:'Babies'?from?routingKey?:?lazy.dog [lazy.#]?Received?message?:'Hello'?from?routingKey?:?lazy.black.pig [*.orange.*]?Received?message?:'Guys'?from?routingKey?:?lazy.black.pig [*.*.rabbit]?Received?message?:'Girls'?from?routingKey?:?lazy.black.pig [lazy.#]?Received?message?:'Babies'?from?routingKey?:?lazy.black.pig

本文轉(zhuǎn)自 genuinecx 51CTO博客，原文鏈接：http://blog.51cto.com/favccxx/1703031，如需轉(zhuǎn)載請自行聯(lián)系原作者

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