JeroMQ: trying to get a client/server sample working

[olze oli]

I tried to get JeroMQ working for my little project. It is a UI and a backend server which handles the logic. But i can not get a JeroMQ Server/Client communication working.

package com.gitlab.jsfdl.jsfdl.jeromq;


import org.zeromq.ZContext;
import org.zeromq.ZMQ;

public class Server {

    ZContext context = new ZContext(1);
    ZMQ.Socket socket = context.createSocket(ZMQ.PAIR);

    public static void main(String args[]) {
        Server server = new Server();
        server.start();

    }

    public void start() {

        // Socket to talk to clients
        socket.bind("tcp://*:10101");
        byte[] recv = socket.recv();
        System.out.println("Received " + new String(recv));
    }

    public void stop() {
        socket.close();
        context.close();
    }
}

package com.gitlab.jsfdl.jsfdl.jeromq;

import org.zeromq.ZContext;
import org.zeromq.ZMQ;

public class Client {

    ZContext context = new ZContext(1);
    ZMQ.Socket socket = context.createSocket(ZMQ.PAIR);

    public void sendMessage() {
        socket.connect("tcp://127.0.0.1:10101");
//        byte[] recv = socket.recv();
//        if (recv != null) {
//            System.out.println("received: " + new String(recv));
//        }
        boolean b =  socket.send("hi");
        System.out.println("Sent with return: " + b);
    }

    public static void main(String args[]) {
        Client client = new Client();
        client.sendMessage();
    }

}

I can connect to the server in the client and also send() returns true, but on the server side i never get to "Received ..."
Can someone tell me what is wrong?

[Norm Radder]

Is there a forum for JeroMQ questions?  Have you tried there?

[olze oli]

no, there is no forum. if there would be such, i would not have posted here.

[Norm Radder]

Can you post the API doc for the classes and packages you are using.

[olze oli]

There is no API doc - jeromq implements zeromq (http://zeromq.org/intro:read-the-manual)
The only documentation is the bible (link above) and the junit samples https://github.com/zeromq/jeromq/tree/master/src/test/java/guide

[Norm Radder]

Ok, maybe there will be some one that is interested to read that.

Otherwise I'd suggest that you write the code using standard java SE classes.

[olze oli]

I do not want to force others (if they want to implement their own UI) to use java. Unfortunately, REST is not really useful for that scenario. Therefore i prefer some kind of bytestream protocol which can be used in other languages too (zeromq is available for many languages, no brokerserver required etc.)

[olze oli]

I found the solution. The client got closed too fast. When send() is called, it returns true meaning: "the message got queued", but that does not mean it got sent. Therefore, implementing autocloseable on the client and closing the ZContext made it.

[Eric Do]

Hi Olze, can you show the code on how to fix it? I'm having the same problem. Thanks