文章出處: http://blog.csdn.net/lmj623565791/article/details/37669573 致敬作者
上一篇博客我們建立了一個簡單的日誌系統,我們能夠廣播日誌消息給所有你的接收者,如果你不瞭解,請查看:RabbitMQ
(三) 發佈/訂閱。本篇博客我們準備給日誌系統添加新的特性,讓日誌接收者能夠訂閱部分消息。例如,我們可以僅僅將致命的錯誤寫入日誌文件,然而仍然在控制面板上打印出所有的其他類型的日誌消息。
1、綁定(Bindings)
在上一篇博客中我們已經使用過綁定。類似下面的代碼:channel.queueBind(queueName, EXCHANGE_NAME, "");綁定表示轉發器與隊列之間的關係。我們也可以簡單的認爲:隊列對該轉發器上的消息感興趣。綁定可以附帶一個額外的參數routingKey。爲了與避免basicPublish方法(發佈消息的方法)的參數混淆,我們準備把它稱作綁定鍵(binding key)。下面展示如何使用綁定鍵(binding key)來創建一個綁定:channel.queueBind(queueName, EXCHANGE_NAME, "black");綁定鍵的意義依賴於轉發器的類型。對於fanout類型,忽略此參數。
2、直接轉發(Direct exchange)
上一篇的日誌系統廣播所有的消息給所有的消費者。我們希望可以對其擴展,來允許根據日誌的嚴重性進行過濾日誌。例如:我們可能希望把致命類型的錯誤寫入硬盤,而不把硬盤空間浪費在警告或者消息類型的日誌上。之前我們使用fanout類型的轉發器,但是並沒有給我們帶來更多的靈活性:僅僅可以愚蠢的轉發。我們將會使用direct類型的轉發器進行替代。direct類型的轉發器背後的路由轉發算法很簡單:消息會被推送至綁定鍵(binding key)和消息發佈附帶的選擇鍵(routing key)完全匹配的隊列。圖解:
上圖,我們可以看到direct類型的轉發器與兩個隊列綁定。第一個隊列與綁定鍵orange綁定,第二個隊列與轉發器間有兩個綁定,一個與綁定鍵black綁定,另一個與green綁定鍵綁定。
這樣的話,當一個消息附帶一個選擇鍵(routing key) orange發佈至轉發器將會被導向到隊列Q1。消息附帶一個選擇鍵(routing key)black或者green將會被導向到Q2.所有的其他的消息將會被丟棄。
3、多重綁定(multiple bindings)
使用一個綁定鍵(binding key)綁定多個隊列是完全合法的。如上圖,一個附帶選擇鍵(routing key)的消息將會被轉發到Q1和Q2。
4、發送日誌(Emittinglogs)
我們準備將這種模式用於我們的日誌系統。我們將消息發送到direct類型的轉發器而不是fanout類型。我們將把日誌的嚴重性作爲選擇鍵(routing key)。這樣的話,接收程序可以根據嚴重性來選擇接收。我們首先關注發送日誌的代碼:
像以前一樣,我們需要先創建一個轉發器:
channel.exchangeDeclare(EXCHANGE_NAME,"direct");
然後我們準備發送一條消息:
channel.basicPublish(EXCHANGE_NAME,severity, null, message.getBytes());
爲了簡化代碼,我們假定‘severity’是‘info’,‘warning’,‘error’中的一個。
5、訂閱
接收消息的代碼和前面的博客的中類似,只有一點不同:我們給我們所感興趣的嚴重性類型的日誌創建一個綁定。
StringqueueName = channel.queueDeclare().getQueue();
for(Stringseverity : argv)
{
channel.queueBind(queueName, EXCHANGE_NAME, severity);
}
6、完整的實例
發送端:EmitLogDirect.java
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package com.zhy.rabbit._04_binding_key;
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import java.util.Random;
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import java.util.UUID;
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import com.rabbitmq.client.Channel;
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import com.rabbitmq.client.Connection;
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import com.rabbitmq.client.ConnectionFactory;
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public class EmitLogDirect
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{
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private static final String EXCHANGE_NAME = "ex_logs_direct";
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private static final String[] SEVERITIES = { "info", "warning", "error" };
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public static void main(String[] argv) throws java.io.IOException
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{
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ConnectionFactory factory = new ConnectionFactory();
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factory.setHost("localhost");
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Connection connection = factory.newConnection();
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Channel channel = connection.createChannel();
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channel.exchangeDeclare(EXCHANGE_NAME, "direct");
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for (int i = 0; i < 6; i++)
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{
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String severity = getSeverity();
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String message = severity + "_log :" + UUID.randomUUID().toString();
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channel.basicPublish(EXCHANGE_NAME, severity, null, message
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.getBytes());
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System.out.println(" [x] Sent '" + message + "'");
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}
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channel.close();
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connection.close();
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}
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private static String getSeverity()
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{
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Random random = new Random();
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int ranVal = random.nextInt(3);
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return SEVERITIES[ranVal];
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}
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}
隨機發送6條隨機類型(routing key)的日誌給轉發器~~
接收端:ReceiveLogsDirect.java
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package com.zhy.rabbit._04_binding_key;
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import java.util.Random;
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import com.rabbitmq.client.Channel;
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import com.rabbitmq.client.Connection;
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import com.rabbitmq.client.ConnectionFactory;
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import com.rabbitmq.client.QueueingConsumer;
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public class ReceiveLogsDirect
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{
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private static final String EXCHANGE_NAME = "ex_logs_direct";
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private static final String[] SEVERITIES = { "info", "warning", "error" };
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public static void main(String[] argv) throws java.io.IOException,
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java.lang.InterruptedException
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{
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ConnectionFactory factory = new ConnectionFactory();
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factory.setHost("localhost");
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Connection connection = factory.newConnection();
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Channel channel = connection.createChannel();
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channel.exchangeDeclare(EXCHANGE_NAME, "direct");
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String queueName = channel.queueDeclare().getQueue();
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String severity = getSeverity();
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channel.queueBind(queueName, EXCHANGE_NAME, severity);
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System.out.println(" [*] Waiting for "+severity+" logs. To exit press CTRL+C");
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QueueingConsumer consumer = new QueueingConsumer(channel);
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channel.basicConsume(queueName, true, consumer);
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while (true)
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{
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QueueingConsumer.Delivery delivery = consumer.nextDelivery();
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String message = new String(delivery.getBody());
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System.out.println(" [x] Received '" + message + "'");
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}
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}
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private static String getSeverity()
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{
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Random random = new Random();
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int ranVal = random.nextInt(3);
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return SEVERITIES[ranVal];
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}
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}
接收端隨機設置一個日誌嚴重級別(binding_key)。。。
我開啓了3個接收端程序,兩個準備接收error類型日誌,一個接收info類型日誌,然後運行發送端程序
運行結果:
[x] Sent 'error_log :d142b096-46c0-4380-a1d2-d8b2ac136a9c'
[x] Sent 'error_log :55ee1fc4-c87c-4e5e-81ba-49433890b9ce'
[x] Sent 'error_log :d01877d6-87c7-4e0a-a109-697d122bc4c9'
[x] Sent 'error_log :b42471b1-875c-43f1-b1ea-0dd5b49863f3'
[x] Sent 'info_log :a6c1bc87-efb0-43eb-8314-8a74c345ed05'
[x] Sent 'info_log :b6a84b6a-353e-4e88-8c23-c791d93b44be'
------------------------------------------------------------------------------------
[*] Waiting for error logs. To exit press CTRL+C
[x] Received 'error_log :d142b096-46c0-4380-a1d2-d8b2ac136a9c'
[x] Received 'error_log :55ee1fc4-c87c-4e5e-81ba-49433890b9ce'
[x] Received 'error_log :d01877d6-87c7-4e0a-a109-697d122bc4c9'
[x] Received 'error_log :b42471b1-875c-43f1-b1ea-0dd5b49863f3'
------------------------------------------------------------------------------------
[*] Waiting for error logs. To exit press CTRL+C
[x] Received 'error_log :d142b096-46c0-4380-a1d2-d8b2ac136a9c'
[x] Received 'error_log :55ee1fc4-c87c-4e5e-81ba-49433890b9ce'
[x] Received 'error_log :d01877d6-87c7-4e0a-a109-697d122bc4c9'
[x] Received 'error_log :b42471b1-875c-43f1-b1ea-0dd5b49863f3'
------------------------------------------------------------------------------------
[*] Waiting for info logs. To exit press CTRL+C
[x] Received 'info_log :a6c1bc87-efb0-43eb-8314-8a74c345ed05'
[x] Received 'info_log :b6a84b6a-353e-4e88-8c23-c791d93b44be'
可以看到我們實現了博文開頭所描述的特性,接收者可以自定義自己感興趣類型的日誌。
其實文章這麼長就在說:發送消息時可以設置routing_key,接收隊列與轉發器間可以設置binding_key,接收者接收與binding_key與routing_key相同的消息。