Proper n tiered exception handling

[Brian McGovern]

I'm looking to get a handle on best exception handling practices in my app.  
Kinda beginner question i guess, sorry.

Im catching the various sql and naming exceptions in the data classes and 
logging and throwing a custom exception called ApplicationException which is 
blank and provided below.  I've read up but an still a little confused on how 
exactly to build this exception class to extend the available struts exception 
classes that would gracefully map to an error display jsp where i could display 
the error to the user.  Right now I just get the HTTP status 500 strack trace 
on the screen.  

Controller snippet that catches the data obj's thrown ApplicationException:
------------------------------------------------------------------------
try {
        zRepBeanBn = 
MyData.getRepByID(StringUtils.convertToInt(request.getParameter("RepID")));
}catch (ApplicationException zAppEx){
        throw zAppEx;
}
------------------------------------------------------------------------

ApplicationException that needs work:  How do I extend this?
------------------------------------------------------------------------
public class ApplicationException extends Exception {
    public ApplicationException(String message) {  }
}
------------------------------------------------------------------------

Thanks