collection to collection

spring-binding/src/main/java/org/springframework/binding/convert/converters/CollectionToCollection.java

@@ -0,0 +1,79 @@
+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;
+
+public class CollectionToCollection implements Converter {
+
+	private ConversionService conversionService;
+
+	public CollectionToCollection(ConversionService conversionService) {
+		this.conversionService = conversionService;
+	}
+
+	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;
+	}
+
+	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 (JdkVersion.isAtLeastJava15()) {
+			Class elementType = GenericCollectionTypeResolver.getCollectionType(targetClass);
+			if (elementType != null) {
+				Class componentType = source.getClass().getComponentType();
+				return conversionService.getConversionExecutor(componentType, elementType);
+			}
+		}
+		return null;
+	}
+
+}