title: How to respond based on arguments in java constructor
body: <p>I have a MVC type architecture for new user registration to my app.
  The user submits the registration form to the controller servlet. This servlet extracts the user parameters and passes them to a class constructor, which represents (and returns) a template(or dummy) user with all the fields initialized based on the arguments.</p>
  
  <p>I remember people insisting on argument validation in methods or constructors before using them.
  Now I try to check the arguments for their validity(for example they are not null).
  So when I find any argument having invalid value, How do I notify the servlet that this particular argument is invalid, because I cannot return a value from the constructor.</p>
  
  <p>Please help me.</p>