Example 8.14 Value Object Factory Strategy - Factory Class

import java.util.HashMap;
import java.lang.*;

/**
* The factory class that creates a value object for a
* given EJB.
*/
public class ValueObjectFactory {

/**
* Use a HashMap to cache class information for
* value object classes
*/
private static HashMap classDataInfo = new HashMap();

/**
* Create a value object for the given object. The
* given object must be an EJB Implementation and have
* a superclass that acts as the class for the entityÕs
* value object. Only the fields defined in this
* superclass are copied in to the value object.
*/
public static java.io.Serializable
  createValueObject(Object ejb, 
    String whichVOType,
    String completeVOType) {
      try {
      // Get the class data for the complete 
      // value object type 
      ClassData cData = getClassData (completeVOType); 

      // Get class data for the requested VO type
      ClassData voCData = getClassData (whichVOType);

      // Create the value object of the requested 
      // value object type...
      java.lang.Object whichVO =       
          Class.forName(whichVOType).newInstance();

      // get the VO fields for the requested VO
      // from the ClassData for the requested VO
      java.lang.reflect.Field[] voFields = 
                  voCData.arrFields;

      // get all fields for the complete VO
      // from the ClassData for complete VO
      java.lang.reflect.Field[] beanFields = 
                  cData.arrFields;

      // copy the common fields from the complete VO 
      // to the fields of the requested VO
      for (int i = 0; i < voFields.length; i++) {
        try {
          String voFieldName = voFields[i].getName();
          for (int j=0; j < beanFields.length; j++) {
            // if the field names are same, copy value
            if ( voFieldName.equals( 
                  beanFields[j].getName())) {
              // Copy value from matching field
              // from the bean instance into the new
              // value object created earlier
              voFields[i].set(whichVO, 
                    beanFields[j].get(ejb));
              break;
            }
          }
        } catch (Exception e) {
          // handle exceptions that may be thrown
          // by the reflection methods...
        }
      }
    // return the requested value object
    return (java.io.Serializable)whichVO;
  } catch (Exception ex) { 
    // Handle all exceptions here...
  }
  return null;
}

/**
* Return a ClassData object that contains the 
* information needed to create
* a value object for the given class. This information
* is only obtained from the
* class using reflection once, after that it will be 
* obtained from the classDataInfo HashMap.
*/
private static ClassData getClassData(String 
  className){

  ClassData cData = 
    (ClassData)classDataInfo.get(className);

  try {
    if (cData == null) {
      // Get the class of the given object and the 
      // value object to be created
      java.lang.reflect.Field[] arrFields ;
      java.lang.Class ejbVOClass = 
          Class.forName(className);

      // Determine the fields that must be copied
      arrFields = ejbVOClass.getDeclaredFields();

      cData = new ClassData(ejbVOClass, arrFields);
      classDataInfo.put(className, cData);
    }
  } catch (Exception e) {
    // handle exceptions here...
  }
  return cData;
  }
}

/**
* Inner Class that contains class data for the
* value object classes
*/
class ClassData {
  // value object Class
  public Class    clsValueObject;

  // value object fields
  public java.lang.reflect.Field[] arrFields;

  // Constructor
  public ClassData(Class cls, 
      java.lang.reflect.Field[] fields) {
    clsValueObject = cls;
    arrFields = fields;
  }
}