Rethrowing exceptions in Java without losing the stack trace

catch (WhateverException e) {
    throw e;
}

will simply rethrow the exception you've caught (obviously the surrounding method has to permit this via its signature etc.). The exception will maintain the original stack trace.

You can also wrap the exception in another one AND keep the original stack trace by passing in the Exception as a Throwable as the cause parameter:

try
{
   ...
}
catch (Exception e)
{
     throw new YourOwnException(e);
}