validator in LookupDispachAction

[jophy john]

Hi
My form contains four submit buttons and I'm using LookupDispatchAction For validation I'm using validation.xml file But the validation needed for each button is different
New+ save the fields should not be empty
For Edit, field shud be empty and then for save field shouldn't be empty
So if I write required validation , then when I click on edit its showing the message which I have given for save since all are submit buttons

So can anybody tel me how I can solve this problem !

Thanx in advance
jophy