Re: Detecting server on lan

Michal Kleczek <>
Fri, 03 Jul 2009 17:17:53 +0200
Ken T. wrote:

On Fri, 03 Jul 2009 15:13:42 +0200, Michal Kleczek wrote:

Tom Anderson wrote:


zeroconf *is* a better way. AppleTalk did something almost identical
twenty years ago, which made it far and away the easiest networking
system to use. When Sun invented RPC, they tried to at least get rid of
fixed ports by using a port mapper. SRV records and all the kinds of
directory service are also attempts to move away from the fixed-address
concept. There is a long, long history of serious efforts to do the
exact opposite of what you suggest.

And Sun did invent something better as well - technology called Jini.
For some reason it is not as widely used as it deserves.

To answer OP's question:
0. Read 1. Implement you
server as a Jini service 2. Implement your client as a Jini client 3.
Run a lookup service on your network 4. You're done :)

This is all getting far too complex for the problem I'm trying to solve.
I'll look into multi-cast udp and see if that solves the problem.

It may look like it's complex but look at the code below. It achieves
everything you need without doing any low level network programming (and it
is not an easy thing to do actually).
The only thing needed is a lookup service running somewhere on the network.
Implementation of a lookup service is part of Jini Starter Kit (it's called
Reggie). The simplest thing to do is to run it on the same machine as your

public interface MyServiceInterface extends Remote {
  public void myMethod() throws RemoteException;

public class TestServer implements MyServiceInterface {

  private final MyServiceInterface myProxy;
  private final JoinManager joinManager;

  public TestServer() throws ExportException, IOException {
    final Exporter exporter = new BasicJeriExporter(
      TcpServerEndpoint.getInstance(0), new BasicILFactory());
    myProxy = (MyServiceInterface) exporter.export(this);
    joinManager =
      new JoinManager(myProxy, null, (ServiceID)null,
        new LookupDiscovery(LookupDiscovery.ALL_GROUPS),
          new LeaseRenewalManager());

  public void myMethod() {

  private synchronized void justStayAlive() throws InterruptedException {

  public static void main(String[] args) throws Exception {
    new TestServer().justStayAlive();


public class TestClient {
  public static void main(String args[]) throws Exception {

    final ServiceDiscoveryManager sdm =
      new ServiceDiscoveryManager(
        new LookupDiscovery(
          LookupDiscovery.ALL_GROUPS), new LeaseRenewalManager());

    //wait forever for a server
    final ServiceItem item = sdm.lookup(
      new ServiceTemplate(
        null, new Class[] {MyServiceInterface.class}, null),
        null, Long.MAX_VALUE);

    if (item != null) {
      MyServiceInterface myService = (MyServiceInterface) item.service;




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