problems with readObject and EOF Exception

Hi,
I'm a Java-beginner and I'm writing a small client/server software and
I'm in troubles looping on
readObject:
-- I have a client that connects to the server and read an object (an
HashMap)
from the server; after that it have to loop on the readObject waiting
for another
HashMap that the server will (or will not) send.
-- The server when the client connect, sends the HashMap, and in case
other clients connect
it will update the HashMap and re-send it to the clients.

I need that the client, after it receive the first object, waits for
another incoming object:
but after reading the first object, readObject throws an EOF
Exception.
How can I handle thi Exception to continue looping on the
readObject(), waiting for a possible
update from the server?

Sorry for my english, and thanks to anyone who will help me coming out
this situation!

Regards
G.

(an extract of code follows)

[CLIENT]
.....
try{
  while(true){
                 fileHashMap = is_obj.readObject();
                 .......
                // Working on the HashMap
                .......
                }
    } catch (ClassNotFoundException e) {
                e.printStackTrace();
       } catch (IOException e) {
                  e.printStackTrace();
       }
[SERVER]
......
//I'm in a function that I call every time that the map is updated

c.os_obj.writeObject(Mappa);
c.os_obj.flush();
c.os_obj.reset();
//END