RabbitMQ （四）路由选择 (Routing) -摘自网络

本篇博客我们准备给日志系统添加新的特性，让日志接收者能够订阅部分消息。例如，我们可以仅仅将致命的错误写入日志文件，然而仍然在控制面板上打印出所有的其他类型的日志消息。

1、绑定（Bindings）

在上一篇博客中我们已经使用过绑定。类似下面的代码： channel.queueBind(queueName, EXCHANGE_NAME, ""); 绑定表示转发器与队列之间的关系。我们也可以简单的认为：队列对该转发器上的消息感兴趣。绑定可以附带一个额外的参数routingKey。为了与避免basicPublish方法（发布消息的方法）的参数混淆，我们准备把它称作绑定键（binding key）。下面展示如何使用绑定键（binding key）来创建一个绑定： channel.queueBind(queueName, EXCHANGE_NAME, "black"); 绑定键的意义依赖于转发器的类型。对于fanout类型，忽略此参数。

2、直接转发（Direct exchange）

上一篇的日志系统广播所有的消息给所有的消费者。我们希望可以对其扩展，来允许根据日志的严重性进行过滤日志。例如：我们可能希望把致命类型的错误写入硬盘，而不把硬盘空间浪费在警告或者消息类型的日志上。之前我们使用fanout类型的转发器，但是并没有给我们带来更多的灵活性：仅仅可以愚蠢的转发。我们将会使用direct类型的转发器进行替代。direct类型的转发器背后的路由转发算法很简单：消息会被推送至绑定键（binding key）和消息发布附带的选择键（routing key）完全匹配的队列。图解：

上图，我们可以看到direct类型的转发器与两个队列绑定。第一个队列与绑定键orange绑定，第二个队列与转发器间有两个绑定，一个与绑定键black绑定，另一个与green绑定键绑定。这样的话，当一个消息附带一个选择键（routing key） orange发布至转发器将会被导向到队列Q1。消息附带一个选择键（routing key）black或者green将会被导向到Q2.所有的其他的消息将会被丢弃。

3、多重绑定（multiple bindings）

使用一个绑定键（binding key）绑定多个队列是完全合法的。如上图，一个附带选择键（routing key）的消息将会被转发到Q1和Q2。

4、发送日志（Emittinglogs）

我们准备将这种模式用于我们的日志系统。我们将消息发送到direct类型的转发器而不是fanout类型。我们将把日志的严重性作为选择键（routing key）。这样的话，接收程序可以根据严重性来选择接收。我们首先关注发送日志的代码：

像以前一样，我们需要先创建一个转发器：

channel.exchangeDeclare(EXCHANGE_NAME,"direct");

然后我们准备发送一条消息：

channel.basicPublish(EXCHANGE_NAME,severity, null, message.getBytes());

为了简化代码，我们假定‘severity’是‘info’，‘warning’，‘error’中的一个。

5、订阅

接收消息的代码和前面的博客的中类似，只有一点不同：我们给我们所感兴趣的严重性类型的日志创建一个绑定。

StringqueueName = channel.queueDeclare().getQueue();

for(Stringseverity : argv)

{

channel.queueBind(queueName, EXCHANGE_NAME, severity);

}

6、完整的实例

发送端：EmitLogDirect.java

package com.zhy.rabbit._04_binding_key;
import java.util.Random;
import java.util.UUID;
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;
public class EmitLogDirect
{
private static final String EXCHANGE_NAME = "ex_logs_direct";
private static final String[] SEVERITIES = { "info", "warning", "error" };
public static void main(String[] argv) throws java.io.IOException
{
// 创建连接和频道
ConnectionFactory factory = new ConnectionFactory();
factory.setHost("localhost");
Connection connection = factory.newConnection();
Channel channel = connection.createChannel();
// 声明转发器的类型
channel.exchangeDeclare(EXCHANGE_NAME, "direct");
//发送6条消息
for (int i = 0; i < 6; i++)
{
String severity = getSeverity();
String message = severity + "_log :" + UUID.randomUUID().toString();
// 发布消息至转发器，指定routingkey
channel.basicPublish(EXCHANGE_NAME, severity, null, message
.getBytes());
System.out.println(" [x] Sent '" + message + "'");
}
channel.close();
connection.close();
}
/**
* 随机产生一种日志类型
*
* @return
*/
private static String getSeverity()
{
Random random = new Random();
int ranVal = random.nextInt(3);
return SEVERITIES[ranVal];
}
}

package com.zhy.rabbit._04_binding_key;

import java.util.Random;

import java.util.UUID;

import com.rabbitmq.client.Channel;

import com.rabbitmq.client.Connection;

import com.rabbitmq.client.ConnectionFactory;

public class EmitLogDirect

{

	private static final String EXCHANGE_NAME = "ex_logs_direct";

	private static final String[] SEVERITIES = { "info", "warning", "error" };

	public static void main(String[] argv) throws java.io.IOException

	{

		// 创建连接和频道

		ConnectionFactory factory = new ConnectionFactory();

		factory.setHost("localhost");

		Connection connection = factory.newConnection();

		Channel channel = connection.createChannel();

		// 声明转发器的类型

		channel.exchangeDeclare(EXCHANGE_NAME, "direct");

		//发送6条消息

		for (int i = 0; i < 6; i++)

		{

			String severity = getSeverity();

			String message = severity + "_log :" + UUID.randomUUID().toString();

			// 发布消息至转发器，指定routingkey

			channel.basicPublish(EXCHANGE_NAME, severity, null, message

					.getBytes());

			System.out.println(" [x] Sent '" + message + "'");

		}

		channel.close();

		connection.close();

	}

	/**

	 * 随机产生一种日志类型

	 *

	 * @return

	 */

	private static String getSeverity()

	{

		Random random = new Random();

		int ranVal = random.nextInt(3);

		return SEVERITIES[ranVal];

	}

}

随机发送6条随机类型（routing key）的日志给转发器~~

接收端：ReceiveLogsDirect.java

package com.zhy.rabbit._04_binding_key;
import java.util.Random;
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;
import com.rabbitmq.client.QueueingConsumer;
public class ReceiveLogsDirect
{
private static final String EXCHANGE_NAME = "ex_logs_direct";
private static final String[] SEVERITIES = { "info", "warning", "error" };
public static void main(String[] argv) throws java.io.IOException,
java.lang.InterruptedException
{
// 创建连接和频道
ConnectionFactory factory = new ConnectionFactory();
factory.setHost("localhost");
Connection connection = factory.newConnection();
Channel channel = connection.createChannel();
// 声明direct类型转发器
channel.exchangeDeclare(EXCHANGE_NAME, "direct");
String queueName = channel.queueDeclare().getQueue();
String severity = getSeverity();
// 指定binding_key
channel.queueBind(queueName, EXCHANGE_NAME, severity);
System.out.println(" [*] Waiting for "+severity+" logs. To exit press CTRL+C");
QueueingConsumer consumer = new QueueingConsumer(channel);
channel.basicConsume(queueName, true, consumer);
while (true)
{
QueueingConsumer.Delivery delivery = consumer.nextDelivery();
String message = new String(delivery.getBody());
System.out.println(" [x] Received '" + message + "'");
}
}
/**
* 随机产生一种日志类型
*
* @return
*/
private static String getSeverity()
{
Random random = new Random();
int ranVal = random.nextInt(3);
return SEVERITIES[ranVal];
}
}

package com.zhy.rabbit._04_binding_key;

import java.util.Random;

import com.rabbitmq.client.Channel;

import com.rabbitmq.client.Connection;

import com.rabbitmq.client.ConnectionFactory;

import com.rabbitmq.client.QueueingConsumer;

public class ReceiveLogsDirect

{

	private static final String EXCHANGE_NAME = "ex_logs_direct";

	private static final String[] SEVERITIES = { "info", "warning", "error" };

	public static void main(String[] argv) throws java.io.IOException,

			java.lang.InterruptedException

	{

		// 创建连接和频道

		ConnectionFactory factory = new ConnectionFactory();

		factory.setHost("localhost");

		Connection connection = factory.newConnection();

		Channel channel = connection.createChannel();

		// 声明direct类型转发器

		channel.exchangeDeclare(EXCHANGE_NAME, "direct");

		String queueName = channel.queueDeclare().getQueue();

		String severity = getSeverity();

		// 指定binding_key

		channel.queueBind(queueName, EXCHANGE_NAME, severity);

		System.out.println(" [*] Waiting for "+severity+" logs. To exit press CTRL+C");

		QueueingConsumer consumer = new QueueingConsumer(channel);

		channel.basicConsume(queueName, true, consumer);

		while (true)

		{

			QueueingConsumer.Delivery delivery = consumer.nextDelivery();

			String message = new String(delivery.getBody());

			System.out.println(" [x] Received '" + message + "'");

		}

	}

	/**

	 * 随机产生一种日志类型

	 *

	 * @return

	 */

	private static String getSeverity()

	{

		Random random = new Random();

		int ranVal = random.nextInt(3);

		return SEVERITIES[ranVal];

	}

}

接收端随机设置一个日志严重级别（binding_key）。。。

我开启了3个接收端程序，两个准备接收error类型日志，一个接收info类型日志，然后运行发送端程序

运行结果：

[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 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'

可以看到我们实现了博文开头所描述的特性，接收者可以自定义自己感兴趣类型的日志。

其实文章这么长就在说：发送消息时可以设置routing_key，接收队列与转发器间可以设置binding_key，接收者接收与binding_key与routing_key相同的消息。