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Pure Java implementation of libzmq
There is a newer version: 0.6.0
package zmq;

public class Dealer extends SocketBase
{
    public static class DealerSession extends SessionBase
    {
        public DealerSession(IOThread ioThread, boolean connect,
            SocketBase socket, final Options options,
            final Address addr)
        {
            super(ioThread, connect, socket, options, addr);
        }
    }

    //  Messages are fair-queued from inbound pipes. And load-balanced to
    //  the outbound pipes.
    private final FQ fq;
    private final LB lb;

    //  Have we prefetched a message.
    private boolean prefetched;

    private Msg prefetchedMsg;

    //  Holds the prefetched message.
    public Dealer(Ctx parent, int tid, int sid)
    {
        super(parent, tid, sid);

        prefetched = false;
        options.type = ZMQ.ZMQ_DEALER;

        fq = new FQ();
        lb = new LB();
        //  TODO: Uncomment the following line when DEALER will become true DEALER
        //  rather than generic dealer socket.
        //  If the socket is closing we can drop all the outbound requests. There'll
        //  be noone to receive the replies anyway.
        //  options.delayOnClose = false;

        options.recvIdentity = true;
    }

    @Override
    protected void xattachPipe(Pipe pipe, boolean icanhasall)
    {
        assert (pipe != null);
        fq.attach(pipe);
        lb.attach(pipe);
    }

    @Override
    protected boolean xsend(Msg msg)
    {
        return lb.send(msg, errno);
    }

    @Override
    protected Msg xrecv()
    {
        return xxrecv();
    }

    private Msg xxrecv()
    {
        Msg msg = null;
        //  If there is a prefetched message, return it.
        if (prefetched) {
            msg = prefetchedMsg;
            prefetched = false;
            prefetchedMsg = null;
            return msg;
        }

        //  DEALER socket doesn't use identities. We can safely drop it and
        while (true) {
            msg = fq.recv(errno);
            if (msg == null) {
                return null;
            }
            if ((msg.flags() & Msg.IDENTITY) == 0) {
                break;
            }
        }
        return msg;
    }

    @Override
    protected boolean xhasIn()
    {
        //  We may already have a message pre-fetched.
        if (prefetched) {
            return true;
        }

        //  Try to read the next message to the pre-fetch buffer.
        prefetchedMsg = xxrecv();
        if (prefetchedMsg == null) {
            return false;
        }
        prefetched = true;
        return true;
    }

    @Override
    protected boolean xhasOut()
    {
        return lb.hasOut();
    }

    @Override
    protected void xreadActivated(Pipe pipe)
    {
        fq.activated(pipe);
    }

    @Override
    protected void xwriteActivated(Pipe pipe)
    {
        lb.activated(pipe);
    }

    @Override
    protected void xpipeTerminated(Pipe pipe)
    {
        fq.terminated(pipe);
        lb.terminated(pipe);
    }
}