系列： http://zxb1985.iteye.com/category/267524
在前面的已经提到了一对一的情况;现在一个生产者与多个消费者的情况（Work Queues）。
Work Queues的示意图如下：
对于上图的模型中对于c端的worker来说。RabbitMQ服务器可能一直发送多个消息给一个worker，而另一个可能几乎不做任何事情。这样就会导致一个worker很忙，而另一个却很空闲。这种情况可能都不想出现。如何解决这个问题呢。当然最理想的情况是均匀分配消息给每个worker。我们可能通过channel.basicQos(1)方法（prefetchCount=1）来设置同一时间每次发给一个消息给一个worker。示意图如下：
P端的程序如下：
packagecom.abin.rabbitmq;
importcom.rabbitmq.client.Channel;
importcom.rabbitmq.client.Connection;
importcom.rabbitmq.client.ConnectionFactory;
importcom.rabbitmq.client.MessageProperties;
publicclassNewTask {
privatestaticfinalString TASK_QUEUE_NAME ="task_queue";
publicstaticvoidmain(String[] argv)throwsException {
ConnectionFactory factory =newConnectionFactory();
factory.setHost("localhost");
Connection connection = factory.newConnection();
Channel channel = connection.createChannel();
//声明此队列并且持久化
channel.queueDeclare(TASK_QUEUE_NAME,true,false,false,null);
String message = getMessage(argv);
channel.basicPublish("", TASK_QUEUE_NAME,
MessageProperties.PERSISTENT_TEXT_PLAIN, message.getBytes());//持久化消息
System.out.println(" [x] Sent '"+ message +"'");
channel.close();
connection.close();
}
privatestaticString getMessage(String[] strings) {
if(strings.length <1)
return"Hello World!";
returnjoinStrings(strings," ");
}
privatestaticString joinStrings(String[] strings, String delimiter) {
intlength = strings.length;
if(length ==0)
return"";
StringBuilder words =newStringBuilder(strings[0]);
for(inti =1; i < length; i++) {
words.append(delimiter).append(strings[i]);
}
returnwords.toString();
}
}
多次运行此程序并传入的参数分别为“First message”，“Secondmessage”，“Thirdmessage”，“Fourth message”，“Fifth message”
C端的程序如下：
Java代
packagecom.abin.rabbitmq;
importcom.rabbitmq.client.Channel;
importcom.rabbitmq.client.Connection;
importcom.rabbitmq.client.ConnectionFactory;
importcom.rabbitmq.client.QueueingConsumer;
publicclassWorker {
privatestaticfinalString TASK_QUEUE_NAME ="task_queue";
publicstaticvoidmain(String[] argv)throwsException {
ConnectionFactory factory =newConnectionFactory();
factory.setHost("localhost");
Connection connection = factory.newConnection();
Channel channel = connection.createChannel();
//声明此队列并且持久化
channel.queueDeclare(TASK_QUEUE_NAME,true,false,false,null);
System.out.println(" [*] Waiting for messages. To exit press CTRL+C");
channel.basicQos(1);//告诉RabbitMQ同一时间给一个消息给消费者
/* We're about to tell the server to deliver us the messages from the queue.
* Since it will push us messages asynchronously,
* we provide a callback in the form of an object that will buffer the messages
* until we're ready to use them. That is what QueueingConsumer does.*/
QueueingConsumer consumer =newQueueingConsumer(channel);
/*
把名字为TASK_QUEUE_NAME的Channel的值回调给QueueingConsumer,即使一个worker在处理消息的过程中停止了，这个消息也不会失效
*/
channel.basicConsume(TASK_QUEUE_NAME,false, consumer);
while(true) {
QueueingConsumer.Delivery delivery = consumer.nextDelivery();//得到消息传输信息
String message =newString(delivery.getBody());
System.out.println(" [x] Received '"+ message +"'");
doWork(message);
System.out.println(" [x] Done");
channel.basicAck(delivery.getEnvelope().getDeliveryTag(),false);//下一个消息
}
}
privatestaticvoiddoWork(String task)throwsInterruptedException {
for(charch : task.toCharArray()) {
if(ch =='.')
Thread.sleep(1000);//这里是假装我们很忙
}
}
}
开启两个worker分别运行。运行结果如：
c1的结果：
Java代码
[*] Waitingformessages. To exit press CTRL+C
[x] Received'First message'
[x] Received'Third message'
[x] Received'Fifth message'
c2的结果
[*] Waitingformessages. To exit press CTRL+C
[x] Received'Second message'
[x] Received'Fourth message'
在前面的Work Queue中的消息是均匀分配消息给消费者；如果我想把消息分发给所有的消费者呢？那应当怎么操作呢？这就是要下面提到的Publish/Subscribe（分布/订阅）。让我们开始Publish/Subscribe之旅吧!
Publish/Subscribe的工作示意图如下：
在上图中的X表示Exchange(交换区);Exchange的类型有：direct,topic,headers和fanout
Publish/Subscribe的Exchang的类型为fanout;声明Publish/Subscribe的Exchang代码如下：
channel.exchangeDeclare("logs","fanout");
对于Work Queue中提到的发布消息的代码如下：
Java代码
channel.basicPublish("", queueName,null, message.getBytes());
但对于Publish/Subscribe中发布消息中的Queue的使用的是默认的；代码如下：
Java代码
channel.basicPublish("logs","",null, message.getBytes());
Exchange和各Queue之间是如何通信的呢？主要是通过把Exchange和各Queue绑定（binding）；示意代码如下:
Java代码
channel.queueBind(queueName, exchangeName,"");
Publish/Subscribe加入绑定的工作示意图如下：
那我们就开始程序代码吧：P端的代码如下：
Java代码
packagecom.abin.rabbitmq;
importcom.rabbitmq.client.Channel;
importcom.rabbitmq.client.Connection;
importcom.rabbitmq.client.ConnectionFactory;
publicclassEmitLog {
privatestaticfinalString EXCHANGE_NAME ="logs";
publicstaticvoidmain(String[] argv)throwsException {
ConnectionFactory factory =newConnectionFactory();
factory.setHost("localhost");
Connection connection = factory.newConnection();
Channel channel = connection.createChannel();
channel.exchangeDeclare(EXCHANGE_NAME,"fanout");//声明Exchange
for(inti =0; i <=2; i++) {
String message ="hello word!"+ i;
channel.basicPublish(EXCHANGE_NAME,"",null, message.getBytes());
System.out.println(" [x] Sent '"+ message +"'");
}
channel.close();
connection.close();
}
}
运行结果如下：
[x] Sent'hello word!0'
[x] Sent'hello word!1'
[x] Sent'hello word!2'
C端的代码如下：
Java代码
packagecom.abin.rabbitmq;
importcom.rabbitmq.client.Channel;
importcom.rabbitmq.client.Connection;
importcom.rabbitmq.client.ConnectionFactory;
importcom.rabbitmq.client.QueueingConsumer;
publicclassReceiveLogsOne {
privatestaticfinalString EXCHANGE_NAME ="logs";
publicstaticvoidmain(String[] argv)throwsException {
ConnectionFactory factory =newConnectionFactory();
factory.setHost("localhost");
Connection connection = factory.newConnection();
Channel channel = connection.createChannel();
channel.exchangeDeclare(EXCHANGE_NAME,"fanout");
String queueName ="log-fb1";
channel.queueDeclare(queueName,false,false,false,null);
channel.queueBind(queueName, EXCHANGE_NAME,"");//把Queue、Exchange绑定
QueueingConsumer consumer =newQueueingConsumer(channel);
channel.basicConsume(queueName,true, consumer);
while(true) {
QueueingConsumer.Delivery delivery = consumer.nextDelivery();
String message =newString(delivery.getBody());
System.out.println(" [x] Received '"+ message +"'");
}
}
}
对于C端的代码我写了二个差不多的程序，只需要修改一下queueName。这样就形成了二个Queue;运行结果相同；
运行结果可能如下：
Java代
[x] Received'hello word!0'
[x] Received'hello word!1'
[x] Received'hello word!2'
