1 package hirondelle.web4j.model;

     2 

     3 /**

     4  Thrown when a Model Object (MO) cannot be constructed because of invalid 

     5  constructor arguments.

     6 

     7  <P>Arguments to a MO constructor have two sources: the end user and the 

     8  the database. In both cases, errors in the values of these arguments 

     9  are outside the immediate control of the application. Hence, MO constructors 

    10  should throw a checked exception - (<tt>ModelCtorException</tt>).

    11 

    12  <P>Using a checked exception has the advantage that

    13  it cannot be ignored by the caller.

    14 

    15  Example use case:<br>

    16 <PRE>

    17   //a Model Object constructor 

    18   Blah(String aText, int aID) throws ModelCtorException {

    19     //check validity of all params.

    20     //if one or more params is invalid, throw a ModelCtorException.

    21     //for each invalid param, add a corresponding error message to 

    22     //ModelCtorException. 

    23   }

    24 

    25   //call the Model Object constructor 

    26   try {

    27     Blah blah = new Blah(text, id);

    28   }

    29   catch(ModelCtorException ex){

    30     //place the exception in scope, for subsequent 

    31     //display to the user in a JSP

    32   }

    33 </PRE>

    34 

    35  <P>In the case of an error, the problem arises of how to redisplay the original, 

    36  erroneous user input. The {@link hirondelle.web4j.ui.tag.Populate} tag 

    37  accomplishes this in an elegant manner, simply by recycling the original 

    38  request parameters.

    39 */

    40 public final class ModelCtorException extends AppException {

    41   //empty

    42 }

    43