When does the RMI Client socket be created?

Question

Hi, I have created my own RMIClientSocketFactory and RMIServerSocketFactory, it was just a normal socket with some print statements. Example:
============================================================
public class MyRMIClientSocketFactory implements
RMIClientSocketFactory, Serializable {
private int hashCode = "MyRMIClientSocketFactory".hashCode();
public Socket createSocket(String host, int port) throws IOException {
System.out.println("creating socket to host : " + host + " on port " + port);
return new Socket(host, port);
public boolean equals(Object object) {
if (object instanceof MyRMIClientSocketFactory)
return true;
return false;
public int hashCode() {
return hashCode;
public class MyRMIServerSocketFactory implements RMIServerSocketFactory, Serializable {
private int hashCode = "MyRMIServerSocketFactory".hashCode();
public ServerSocket createServerSocket(int port) throws IOException {
System.out.println("creating ServerSocket on port " + port);
return new ServerSocket(port);
public boolean equals(Object object) {
if (object instanceof MyRMIServerSocketFactory)
return true;
return false;
public int hashCode() {
return hashCode;
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I wonder when the message "creating socket on port.." and "creating ServerSocket on port.." will be printed? And I found that the equals() and hashCode() methods are called quite a lot of times when I made one rmi call. When I keep the reference of the remote object for some times, the client socket will be created again. Can somebody tell me how all these work?
Thanks,
Jax

Answer 1

Does it
means that when timeout happened, a new client socket
will be created and make remote calls to renew DGC
leases?Yes.
Again, about exporting remote objects on the same
port, why I got the exceptions:
java.rmi.server.ExportException: Port already in use:
1234;
nested exception is: java.net.BindException: Address
already in use: JVM_BindYou get this if you try to export two servers on the same port but their server socket factories are not equal (or not both null or unspecified), or if the two ojbects are in separate JVMs (port sharing can only work inside a single JVM), or if the port is in use by some other listening process.
Your MyRMIServerSocketFactory.equals() method looks OK to me, but I'd delete the hashCode() method, it's not necessary for RMI and your implementation is flawed. Personally I use the following equals() method:
public boolean equals(Object that) { return that != null && that.getClass() == this.getClass(); }