ZeroMQ之PUB/SUB模式

参考: http://zguide.zeromq.org/page:all

PUB/SUB模式: 发布/订阅模式。该模式是单向的，发布者send msg, 订阅者receive msg. 一旦有消息发出，pub会发送给所有的sub。.

模式如下图：

可以看出发布者绑定绑定一个端口，订阅者通过连接发布者接受订阅的消息。

官网描述这种模式要注意以下几点：

1. pub/sub模式下，sub事实上可以连接多个pub，每次只连接一个connect，所以接收到的消息可以是叫错的，以至于不会单个pub掩盖了其他pub

2. 如果存在某个pub没有被任何sub连接，则该pub会丢弃所有的消息

3. 如果你采用tcp的连接方式，sub很慢，消息将会堆积在pub，后期会对该问题有个较好的解决

4. 目前的而版本，过滤发生在sub端，而不是pub端，意思就是说一个pub会发送所有的消息到所有的sub, 由sub决定是要drop这个msg.

以下代码显示一个pub 两个sub， Publisher发送两种主题的消息A和B， Sub1接受B主题的消息， Sub2接受A主题的消息。

package pubsub;

import org.zeromq.ZMQ;
import org.zeromq.ZMQ.Context;
import org.zeromq.ZMQ.Socket;

public class Publisher {

    /**
     * @param args
     * @throws InterruptedException 
     */
    public static void main(String[] args) throws InterruptedException {
	// TODO Auto-generated method stub
	Context context = ZMQ.context(1);
	Socket publisher = context.socket(ZMQ.PUB);
	publisher.bind("tcp://*:5557");
	int i = 0;
	while (true) {
	    Thread.currentThread().sleep(1000);
	    publisher.send("A".getBytes(), ZMQ.SNDMORE);
	    publisher.send("This is A".getBytes(), 0);
	    publisher.send("B".getBytes(), ZMQ.SNDMORE);
	    publisher.send("This is B".getBytes(), 0);
	}
    }

}

package pubsub;

import org.zeromq.ZMQ;
import org.zeromq.ZMQ.Context;
import org.zeromq.ZMQ.Socket;

public class Sub1 {

    /**
     * @param args
     */
    public static void main(String[] args) {
	// TODO Auto-generated method stub
	Context context = ZMQ.context(1);
	Socket subscribe = context.socket(ZMQ.SUB);
	subscribe.connect("tcp://127.0.0.1:5557");
	subscribe.subscribe("B".getBytes());
	while (true) {
	    System.out.println(new String(subscribe.recv(0)));
	    System.out.println(new String(subscribe.recv(0)));
	}
    }

}

package pubsub;

import org.zeromq.ZMQ;
import org.zeromq.ZMQ.Context;
import org.zeromq.ZMQ.Socket;

public class Sub2 {
    public static void main(String[] args) {
	// TODO Auto-generated method stub
	Context context = ZMQ.context(1);
	Socket subscribe = context.socket(ZMQ.SUB);
	subscribe.connect("tcp://127.0.0.1:5557");
	//subscribe.subscribe("topic".getBytes());
	subscribe.subscribe("A".getBytes());
	while (true) {
	    System.out.println(new String(subscribe.recv(0)));
	    System.out.println(new String(subscribe.recv(0)));
	}
    }
}

结果显示

Sub1:
B
This is B
B
This is B
B
This is B
B
This is B
...

Sub2:
A
This is A
A
This is A
A
This is A
A
This is A