Programming Jakarta Struts

Performing Presentation Validation

This chapter has touched on performing your application’s input validation in the validate( ) method of the ActionForm. You can create whatever presentation validation rules you need in this method. For example, the LoginForm from Example 7-2 validated that the email and password fields were entered and were not empty strings. Although this is a trivial example, you can validate anything you like. A common validation rule is to ensure that a string value that should be a number is in fact a string representation of a valid number. The validate( ) routine for this rule might look like the one in Example 7-5.

Example 7-5. Performing a number validation rule

public ActionErrors validate(ActionMapping mapping, HttpServletRequest request) {
  ActionErrors errors = new ActionErrors(  );

  String orderQtyStr = getQuantity(  );

  if( orderQtyStr == null || orderQtyStr.length(  ) < 1 ){
    errors.add( ActionErrors.GLOBAL_ERROR,
                new ActionError( "order.quantity.required" ));
  }

  // Validate that the qty entered was in fact a number
  try{
    // Integer.parse was not used because it's not really I18N-safe
    java.text.Format format = java.text.NumberFormat.getNumberInstance(  );
    Number orderQty = (Number)format.parseObject( orderQtyStr );
  }catch( Exception ex ){
    // The quantity entered by the user was not a valid qty
    errors.add( ActionErrors.GLOBAL_ERROR,
                new ActionError( "order.quantity.invalid" ));
  }
  return errors;
}

As you can imagine, web applications often need to check for ...