CollectionToCollection.java :  » J2EE » spring-ide_2.3.0 » org » springframework » binding » convert » converters » Java Open Source

package org.springframework.binding.convert.converters;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Set;
import java.util.SortedSet;
import java.util.TreeSet;

import org.springframework.binding.convert.ConversionExecutor;
import org.springframework.binding.convert.ConversionService;
import org.springframework.core.GenericCollectionTypeResolver;
import org.springframework.core.JdkVersion;

/**
 * A converter that can convert from one collection type to another.
 * 
 * @author Keith Donald
 */
public class CollectionToCollection implements Converter {

  private ConversionService conversionService;

  private ConversionExecutor elementConverter;

  /**
   * Creates a new collection-to-collection converter
   * @param conversionService the conversion service to use to convert collection elements to add to the target
   * collection
   */
  public CollectionToCollection(ConversionService conversionService) {
    this.conversionService = conversionService;
  }

  /**
   * Creates a new collection-to-collection converter
   * @param elementConverter a specific converter to use to convert collection elements added to the target collection
   */
  public CollectionToCollection(ConversionExecutor elementConverter) {
    this.elementConverter = elementConverter;
  }

  public Class getSourceClass() {
    return Collection.class;
  }

  public Class getTargetClass() {
    return Collection.class;
  }

  public Object convertSourceToTargetClass(Object source, Class targetClass) throws Exception {
    if (source == null) {
      return null;
    }
    Class targetCollectionImpl = getCollectionImplClass(targetClass);
    Collection targetCollection = (Collection) targetCollectionImpl.getConstructor(null).newInstance(null);
    ConversionExecutor elementConverter = getElementConverter(source, targetClass);
    Collection sourceCollection = (Collection) source;
    Iterator it = sourceCollection.iterator();
    while (it.hasNext()) {
      Object value = it.next();
      if (elementConverter != null) {
        value = elementConverter.execute(value);
      }
      targetCollection.add(value);
    }
    return targetCollection;
  }

  // this code is duplicated in ArrayToCollection.java and ObjectToCollection too
  private Class getCollectionImplClass(Class targetClass) {
    if (targetClass.isInterface()) {
      if (List.class.equals(targetClass)) {
        return ArrayList.class;
      } else if (Set.class.equals(targetClass)) {
        return LinkedHashSet.class;
      } else if (SortedSet.class.equals(targetClass)) {
        return TreeSet.class;
      } else {
        throw new IllegalArgumentException("Unsupported collection interface [" + targetClass.getName() + "]");
      }
    } else {
      return targetClass;
    }
  }

  private ConversionExecutor getElementConverter(Object source, Class targetClass) {
    if (elementConverter != null) {
      return elementConverter;
    } else {
      if (JdkVersion.isAtLeastJava15()) {
        Class elementType = GenericCollectionTypeResolver.getCollectionType(targetClass);
        if (elementType != null) {
          Class componentType = source.getClass().getComponentType();
          return conversionService.getConversionExecutor(componentType, elementType);
        }
      }
      return null;
    }
  }

}