java - How to find duplicates in an ArrayList which is in the form of JSON object? -

i having option in website user i.e: "settings" in given 3 options(textboxes) enter details: 1.e-mail, 2.sms, 3.mms.. in user can enter mail id: optional thing but, if enter both or same neccesary e-mail , optional or same then, have tell "given e-mail" alredy exist.

i sending data arraylist coverted json object.

what best way find duplicate , notify user

help me in

thanks in advance

either parse java collections json framework of choice, check duplicates or use javascript directly work on json.

if have arraylist anyway, why don't iterate on that?