Binary Star client in Java

import org.zeromq.ZContext;
import org.zeromq.ZMQ;
import org.zeromq.ZMQ.PollItem;
import org.zeromq.ZMQ.Socket;

// Binary Star client proof-of-concept implementation. This client does no
// real work; it just demonstrates the Binary Star failover model.

public class bstarcli
{
private static final long REQUEST_TIMEOUT = 1000; // msecs
private static final long SETTLE_DELAY = 2000; // Before failing over

public static void main(String[] argv) throws Exception
{
ZContext ctx = new ZContext();

String[] server = { "tcp://localhost:5001", "tcp://localhost:5002" };
int serverNbr = 0;

System.out.printf ("I: connecting to server at %s…\n", server [serverNbr]);
Socket client = ctx.createSocket(ZMQ.REQ);
client.connect(server[serverNbr]);

int sequence = 0;
while (!Thread.currentThread().isInterrupted()) {
// We send a request, then we work to get a reply
String request = String.format("%d", ++sequence);
client.send(request);

boolean expectReply = true;
while (expectReply) {
// Poll socket for a reply, with timeout
PollItem items [] = { new PollItem(client, ZMQ.Poller.POLLIN) };
int rc = ZMQ.poll(items, 1, REQUEST_TIMEOUT);
if (rc == -1)
break; // Interrupted

// We use a Lazy Pirate strategy in the client. If there's no
// reply within our timeout, we close the socket and try again.
// In Binary Star, it's the client vote that decides which
// server is primary; the client must therefore try to connect
// to each server in turn:

if (items[0].isReadable()) {
// We got a reply from the server, must match sequence
String reply = client.recvStr();
if (Integer.parseInt(reply) == sequence) {
System.out.printf ("I: server replied OK (%s)\n", reply);
expectReply = false;
Thread.sleep(1000); // One request per second
}
else
System.out.printf ("E: bad reply from server: %s\n", reply);
}
else {
System.out.printf ("W: no response from server, failing over\n");

// Old socket is confused; close it and open a new one
ctx.destroySocket(client);
serverNbr = (serverNbr + 1) % 2;
Thread.sleep(SETTLE_DELAY);
System.out.printf("I: connecting to server at %s…\n",
server[serverNbr]);
client = ctx.createSocket(ZMQ.REQ);
client.connect(server[serverNbr]);

// Send request again, on new socket
client.send(request);
}
}
}
ctx.destroy();

}
}