ZeroMQ之PUB/SUB模式

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   

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