===
信息发布与订阅
Rabbit的核心组件包含Queue(消息队列)和Exchanges两部分，Exchange的主要部分就是对信息进行路由，通过将消息队列绑定到Exchange上，则可以实现订阅形式的消息发布及Publish/Subscribe在这种模式下消息发布者只需要将信息发布到相应的Exchange中，而Exchange则自动将信息分发到不同的Queue当中。
这种模式下Exchange充当的角色
在命令行中可以使用
sudo rabbitmqctl list_exchanges
sudo rabbitmqctl list_bindings
分别查看当前系统种存在的Exchange和Exchange上绑定的Queue信息。
消息发布者EmitLog.java
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;
public class EmitLog {
private static final String EXCHANGE_NAME="logs";
public static void main(String[] args) throws java.io.IOException{
//创建链接工厂
ConnectionFactory factory = new ConnectionFactory();
factory.setHost("localhost");
//创建链接
Connection connection = factory.newConnection();
//创建信息管道
Channel channel = connection.createChannel();
//生命Exchange 非持久化
channel.exchangeDeclare(EXCHANGE_NAME, "fanout");
String message = "Message "+Math.random();
//第一个参数是对应的Exchange名称,如果为空则使用默认Exchange
channel.basicPublish(EXCHANGE_NAME, "", null, message.getBytes());
System.out.println("[x] Sent '"+message+"'");
//关闭链接
channel.close();
connection.close();
}
}
消息消费者ReceiveLogs.java
import java.io.IOException;
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;
import com.rabbitmq.client.ConsumerCancelledException;
import com.rabbitmq.client.QueueingConsumer;
import com.rabbitmq.client.ShutdownSignalException;
public class ReceiveLogs {
private static final String EXCHANGE_NAME = "logs";
public static void main(String[] args) throws IOException, ShutdownSignalException, ConsumerCancelledException, InterruptedException {
//创建链接工厂
ConnectionFactory factory = new ConnectionFactory();
factory.setHost("localhost");
//创建链接
Connection connection = factory.newConnection();
//创建消息管道
Channel channel = connection.createChannel();
//声明Exchange
channel.exchangeDeclare(EXCHANGE_NAME, "fanout");
//利用系统自动声明一个非持久化的消息队列，并返回唯一的队列名称
String queueName = channel.queueDeclare().getQueue();
//将消息队列绑定到Exchange
channel.queueBind(queueName, EXCHANGE_NAME, "");
System.out.println(" [*] Waiting for messages. To exit press CTRL+C");
//声明一个消费者
QueueingConsumer consumer = new QueueingConsumer(channel);
channel.basicConsume(queueName, true, consumer);
while (true) {
//循环获取信息
QueueingConsumer.Delivery delivery = consumer.nextDelivery();
String message = new String(delivery.getBody());
System.out.println(" [x] Received '" + message + "'");
}
}
}
运行时启动一个EmitLog.java多个ReceiveLogs.java则可以看到发布者每次发布信息，只要绑定到了相应Exchange的消费者都可以获取到信息。
RabbitMQ信息持久化技术
上面的例子中我们实现了Publisher/Subscribe的消息分发方式，但是其中存在一些问题。比如当我们运行一个ReceiveLog都对应了一个特定的消息队列，可以利用list_queues进行查看，同时这些消息队列是帮到到名为logs的Exchange中，这是发布消息每个消费者都可以接收到，可以当关闭ReceiveLog程序后这些消息队列就都会自动销毁，因为他们是非持久化的。同样对于EmitLog程序也一样，每次关闭后之前生命的Exchange也将自动销毁。
这就产生了一些问题。如果当ReceiveLog为运行时，此时就并没有一个消息队列是绑定到Exchange上的，在发布消息后再启动ReceiveLog程序是无法接受到之前发布的信息。这就是为什么要进行消息的持久化。
通过持久化技术，我们可以生命一个持久化的Exchange，以及持久化的Queue这样，在把Queue绑定到Exchange后，即使没有消费者程序运行，信息依然能保存在Queue当中，当下次启动消费者程序时依然能获取到发布的所有信息。就好比当一个消费者程序在执行消息序列中的任务时，如果突然出现了异常那么重新启动后，依然能从上一次发生错误的位置继续运行，对于某些需要一个有序性和连续性的操作，这点显的尤为重要。
下面还是给出一个例子，在持久化过程中，可以借助list_exchanges,list_bindings,list_queues来查看服务器中相关信息来帮组分析过程。
Publisher.java
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;
import com.rabbitmq.client.MessageProperties;
public class Publisher {
private static final String EXCHANGE_NAME="persi";//定义Exchange名称
private static final boolean durable = true;//消息队列持久化
public static void main(String[] args) throws java.io.IOException {
ConnectionFactory factory = new ConnectionFactory();//创建链接工厂
factory.setHost("localhost");
Connection connection = factory.newConnection();//创建链接
Channel channel = connection.createChannel();//创建信息通道
channel.exchangeDeclare(EXCHANGE_NAME, "fanout", durable);//创建交换机并生命持久化
String message = "Hello Wrold "+Math.random();
//消息的持久化
channel.basicPublish(EXCHANGE_NAME, "", MessageProperties.PERSISTENT_TEXT_PLAIN, message.getBytes());
System.out.println("[x] Sent '" + message + "'");
channel.close();
connection.close();
}
}
Subscriber.java
public class Subscriber {
//private static final String[] QUEUE_NAMES= {"que_001","que_002","que_003","que_004","que_005"};
private static final String[] QUEUE_NAMES= {"que_006","que_007","que_008","que_009","que_0010"};
public static void main(String[] args){
for(int i=0;i<QUEUE_NAMES.length;i++){
SubscriberThead sub = new SubscriberThead(QUEUE_NAMES[i]);
Thread t = new Thread(sub);
t.start();
}
}
}
SubscriberThead.java
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;
import com.rabbitmq.client.QueueingConsumer;
import com.rabbitmq.client.AMQP.Queue.DeclareOk;
public class SubscriberThead implements Runnable {
private String queue_name = null;
private static final String EXCHANGE_NAME = "persi";// 定义交换机名称
private static final boolean durable = true;//消息队列持久化
public SubscriberThead(String queue_name) {
this.queue_name = queue_name;
}
@Override
public void run() {
try{
ConnectionFactory factory = new ConnectionFactory();
factory.setHost("localhost");
Connection connection = factory.newConnection();
Channel channel = connection.createChannel();
channel.exchangeDeclare(EXCHANGE_NAME, "fanout", durable);
DeclareOk ok = channel.queueDeclare(queue_name, durable, false,
false, null);
String queueName = ok.getQueue();
channel.queueBind(queueName, EXCHANGE_NAME, "");
System.out.println(" ["+queue_name+"] Waiting for messages. To exit press CTRL+C");
channel.basicQos(1);//消息分发处理
QueueingConsumer consumer = new QueueingConsumer(channel);
channel.basicConsume(queueName, false, consumer);
while (true) {
Thread.sleep(2000);
QueueingConsumer.Delivery delivery = consumer.nextDelivery();
String message = new String(delivery.getBody());
System.out.println(" ["+queue_name+"] Received '" + message + "'");
channel.basicAck(delivery.getEnvelope().getDeliveryTag(), false);
}
}catch(Exception e){
e.printStackTrace();
}
}
}
通过持久化处理后rabbitMQ将保存Exchange信息以及Queue信息，甚至在rabbitMQ服务器关闭后信息依然能保存，这样就提供了消息传递的可靠性
