hirondelle.web4j.model
Class ModelCtorException

Object
  Throwable
      Exception
          hirondelle.web4j.model.AppException
              hirondelle.web4j.model.ModelCtorException

All Implemented Interfaces:

MessageList, Serializable

public final class ModelCtorException
extends AppException

Thrown when a Model Object (MO) cannot be constructed because of invalid constructor arguments.

Arguments to a MO constructor have two sources: the end user and the the database. In both cases, errors in the values of these arguments are outside the immediate control of the application. Hence, MO constructors should throw a checked exception - (ModelCtorException).

Using a checked exception has the advantage that it cannot be ignored by the caller. Example use case:

  //a Model Object constructor 
  Blah(String aText, int aID) throws ModelCtorException {
    //check validity of all params.
    //if one or more params is invalid, throw a ModelCtorException.
    //for each invalid param, add a corresponding error message to 
    //ModelCtorException. 
  }

  //call the Model Object constructor 
  try {
    Blah blah = new Blah(text, id);
  }
  catch(ModelCtorException ex){
    //place the exception in scope, for subsequent 
    //display to the user in a JSP
  }

In the case of an error, the problem arises of how to redisplay the original, erroneous user input. The Populate tag accomplishes this in an elegant manner, simply by recycling the original request parameters.

See Also:

Serialized Form

Constructor Summary

ModelCtorException()

Method Summary

Methods inherited from class hirondelle.web4j.model.AppException

add, add, add, getMessages, isEmpty, isNotEmpty, toString

Methods inherited from class Throwable

fillInStackTrace, getCause, getLocalizedMessage, getMessage, getStackTrace, initCause, printStackTrace, printStackTrace, printStackTrace, setStackTrace

Methods inherited from class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

ModelCtorException

public ModelCtorException()