柯南君：看大数据时代下的IT架构（8）消息队列之RabbitMQ--案例（topic起航）

二、Topic(主题) (using the Java client)

上一篇文章中，我们进步改良了我们的日志系统。我们使用direct类型转发器，使得接收者有能力进行选择性的接收日志,，而非fanout那样，只能够无脑的转发。

为了在我们的系统中实现上述的需求，我们需要学习稍微复杂的主题类型的转发器（topic exchange）。

三、Topic exchange（主题转换）

主题类型的转发器的消息不能随意的设置选择键（routing_key），必须是由点隔开的一系列的标识符组成。

标识符可以是任何东西，但是一般都与消息的某些特性相关。一些合法的选择键的例子：

"stock.usd.nyse", "nyse.vmw","quick.orange.rabbit".你可以定义任何数量的标识符，上限为255个字节。

绑定键和选择键的形式一样。主题类型的转发器背后的逻辑和直接类型的转发器很类似：一个附带特殊的选择键将会被转发到绑定键与之匹配的队列中。需要注意的是：关于绑定键有两种特殊的情况。

* 可以匹配一个标识符。
# 可以匹配0个或多个标识符。

下面一个简单的图片实例：

我们准备发送关于动物的消息。消息会附加一个选择键包含3个标识符（两个点隔开）。

第一个标识符描述动物的速度，

第二个标识符描述动物的颜色，

第三个标识符描述动物的物种：<speed>.<color>.<species>。

我们创建3个绑定键：Q1与*.orange.*绑定Q2与*.*.rabbit和lazy.#绑定。:

另一方面，lazy.orange.male.rabbit，虽然是四个标识符，也可以与lazy.#匹配，从而转发至Q2。

注：主题类型的转发器非常强大，可以实现其他类型的转发器。

当一个队列与绑定键#绑定，将会收到所有的消息，类似fanout类型转发器。当绑定键中不包含任何#与*时，类似direct类型转发器

四、Putting it all together（全部代码）

我们要在我们的日志系统，用一个主题转换。我们先假设工作日志的路由键将两个词：<facility>.<severity>。

发送 EmitLogTopic.java:

public class EmitLogTopic {
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 routingKey = getRouting(argv);
String message = getMessage(argv);
channel.basicPublish(EXCHANGE_NAME, routingKey, null, message.getBytes());
System.out.println(" [x] Sent '" + routingKey + "':'" + message + "'");
connection.close();
}
//...
}

接收端：ReceiveLogsTopic.java:

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();
if (argv.length < 1){
System.err.println("Usage: ReceiveLogsTopic [binding_key]...");
System.exit(1);
}
for(String bindingKey : argv){
channel.queueBind(queueName, EXCHANGE_NAME, bindingKey);
}
System.out.println(" [*] Waiting for messages. 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());
String routingKey = delivery.getEnvelope().getRoutingKey();
System.out.println(" [x] Received '" + routingKey + "':'" + message + "'");
}
}
}

Run the following examples, including the classpath as in Tutorial 1 - on Windows, use %CP%.

To receive all the logs:

$ java -cp $CP ReceiveLogsTopic "#"

To receive all logs from the facility "kern":

$ java -cp $CP ReceiveLogsTopic "kern.*"

Or if you want to hear only about "critical" logs:

$ java -cp $CP ReceiveLogsTopic "*.critical"

You can create multiple bindings:

$ java -cp $CP ReceiveLogsTopic "kern.*" "*.critical"

And to emit a log with a routing key "kern.critical" type:

$ java -cp $CP EmitLogTopic "kern.critical" "A critical kernel error"

Have fun playing with these programs. Note that the code doesn't make any assumption about the routing or binding keys, you may want to play with more than two routing key parameters.

Some teasers:

Will "*" binding catch a message sent with an empty routing key?
Will "#.*" catch a message with a string ".." as a key? Will it catch a message with a single word key?
How different is "a.*.#" from "a.#"?

五、注释版的程序实例（全部代码）

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) throws Exception {
ConnectionFactory factory = new ConnectionFactory();
factory.setHost("localhost");
Connection connection = factory.newConnection();
Channel channel = connection.createChannel();
channel.exchangeDeclare(EXCHANGE_NAME, "topic");//声明topic类型的Exchange
String routingKeyOne = "logs.error.one";// 定义一个路由名为“error”
for (int i = 0; i <= 1; i++) {
String messageOne = "this is one error logs:" + i;
channel.basicPublish(EXCHANGE_NAME, routingKeyOne, null, messageOne
.getBytes());
System.out.println(" [x] Sent '" + routingKeyOne + "':'"
+ messageOne + "'");
}
System.out.println("################################");
String routingKeyTwo = "logs.error.two";
for (int i = 0; i <= 2; i++) {
String messageTwo = "this is two error logs:" + i;
channel.basicPublish(EXCHANGE_NAME, routingKeyTwo, null, messageTwo
.getBytes());
System.out.println(" [x] Sent '" + routingKeyTwo + "':'"
+ messageTwo + "'");
}
System.out.println("################################");
String routingKeyThree = "logs.info.one";
for (int i = 0; i <= 3; i++) {
String messageThree = "this is one info logs:" + i;
channel.basicPublish(EXCHANGE_NAME, routingKeyThree, null,
messageThree.getBytes());
System.out.println(" [x] Sent '" + routingKeyThree + "':'"
+ messageThree + "'");
}
channel.close();
connection.close();
}
}

运行结果可能如下：'logs.error.one':'this is one error logs:0'

[x] Sent 'logs.error.one':'this is one error logs:1'
################################
[x] Sent 'logs.error.two':'this is two error logs:0'
[x] Sent 'logs.error.two':'this is two error logs:1'
[x] Sent 'logs.error.two':'this is two error logs:2'
################################
[x] Sent 'logs.info.one':'this is one info logs:0'
[x] Sent 'logs.info.one':'this is one info logs:1'
[x] Sent 'logs.info.one':'this is one info logs:2'
[x] Sent 'logs.info.one':'this is one info logs:3'

第一个C端的代码如下：

package com.abin.rabbitmq;

import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;
import com.rabbitmq.client.QueueingConsumer;

public class ReceiveLogsTopic {
    private static final String EXCHANGE_NAME = "topic_logs";// 定义Exchange名称

    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");// 声明topic类型的Exchange

        String queueName = "queue_topic_logs1";// 定义队列名为“queue_topic_logs1”的Queue
        channel.queueDeclare(queueName, false, false, false, null);
//      String routingKeyOne = "*.error.two";// "error"路由规则
//      channel.queueBind(queueName, EXCHANGE_NAME, routingKeyOne);// 把Queue、Exchange及路由绑定
        String routingKeyTwo = "logs.*.one";//通配所有logs下第三词（最后一个）词为one的消息
        channel.queueBind(queueName, EXCHANGE_NAME, routingKeyTwo);

        System.out.println(" [*] Waiting for messages.");

        QueueingConsumer consumer = new QueueingConsumer(channel);
        channel.basicConsume(queueName, true, consumer);

        while (true) {
            QueueingConsumer.Delivery delivery = consumer.nextDelivery();
            String message = new String(delivery.getBody());
            String routingKey = delivery.getEnvelope().getRoutingKey();

            System.out.println(" [x] Received '" + routingKey + "':'" + message
                    + "'");
        }
    }
}
第二个C端的运行结果如下：
[*] Waiting for messages.
[x] Received 'logs.error.one':'this is one error logs:0'
[x] Received 'logs.error.one':'this is one error logs:1'
[x] Received 'logs.error.two':'this is two error logs:0'
[x] Received 'logs.error.two':'this is two error logs:1'
[x] Received 'logs.error.two':'this is two error logs:2'
[x] Received 'logs.info.one':'this is one info logs:0'
[x] Received 'logs.info.one':'this is one info logs:1'
[x] Received 'logs.info.one':'this is one info logs:2'
[x] Received 'logs.info.one':'this is one info logs:3'