CollectionConverter.java :  » Google-tech » objectify-appengine » com » googlecode » objectify » impl » conv » Java Open Source

package com.googlecode.objectify.impl.conv;

import java.util.ArrayList;
import java.util.Collection;

import com.googlecode.objectify.impl.TypeUtils;


/**
 * Knows how to convert java Collections.  Note that each individual element must be
 * converted. 
 */
public class CollectionConverter implements Converter
{
  /** Need this to convert members */
  Conversions conversions;
  
  /** */
  public CollectionConverter(Conversions conv)
  {
    this.conversions = conv;
  }
  
  @Override
  public Object forDatastore(Object value, ConverterSaveContext ctx)
  {
    if (value instanceof Collection<?>)
    {
      if (ctx.inEmbeddedCollection())
        throw new IllegalStateException("You cannot have collections inside @Embedded arrays or collections");
      
      // All collections get turned into a List that preserves the order.  We must
      // also be sure to convert anything contained in the collection
      ArrayList<Object> list = new ArrayList<Object>(((Collection<?>)value).size());

      for (Object obj: (Collection<?>)value)
        list.add(this.conversions.forDatastore(obj, ctx));
      
      return list;
    }
    else
      return null;
  }

  @Override
  public Object forPojo(Object value, Class<?> fieldType, ConverterLoadContext ctx, Object onPojo)
  {
    if (Collection.class.isAssignableFrom(fieldType) && value instanceof Collection<?>)
    {
      Class<?> componentType = TypeUtils.getComponentType(fieldType, ctx.getField().getGenericType());

      Collection<?> datastoreCollection = (Collection<?>)value;
      Collection<Object> target = TypeUtils.prepareCollection(onPojo, ctx.getField(), datastoreCollection.size());

      for (Object datastoreValue: datastoreCollection)
        target.add(this.conversions.forPojo(datastoreValue, componentType, ctx, onPojo));
      
      return target;
    }
    else
      return null;
  }
}