ConversionService is able to work with "Collections.emptyList()" as target type (again; SPR-7293)

jhoeller · jhoeller · commit 7eeb654eec3a · 2011-12-06T21:18:13.000Z
diff --git a/org.springframework.core/src/main/java/org/springframework/core/convert/support/CollectionToCollectionConverter.java b/org.springframework.core/src/main/java/org/springframework/core/convert/support/CollectionToCollectionConverter.java
@@ -60,6 +60,9 @@ public Object convert(Object source, TypeDescriptor sourceType, TypeDescriptor t
 		}
 		boolean copyRequired = !targetType.getType().isInstance(source);
 		Collection<?> sourceCollection = (Collection<?>) source;
+		if (!copyRequired && sourceCollection.isEmpty()) {
+			return sourceCollection;
+		}
 		Collection<Object> target = CollectionFactory.createCollection(targetType.getType(), sourceCollection.size());
 		if (targetType.getElementTypeDescriptor() == null) {
 			for (Object element : sourceCollection) {
diff --git a/org.springframework.core/src/main/java/org/springframework/core/convert/support/MapToMapConverter.java b/org.springframework.core/src/main/java/org/springframework/core/convert/support/MapToMapConverter.java
@@ -59,6 +59,9 @@ public Object convert(Object source, TypeDescriptor sourceType, TypeDescriptor t
 		}
 		boolean copyRequired = !targetType.getType().isInstance(source);
 		Map<Object, Object> sourceMap = (Map<Object, Object>) source;
+		if (!copyRequired && sourceMap.isEmpty()) {
+			return sourceMap;
+		}
 		Map<Object, Object> targetMap = CollectionFactory.createMap(targetType.getType(), sourceMap.size());
 		for (Map.Entry<Object, Object> entry : sourceMap.entrySet()) {
 			Object sourceKey = entry.getKey();
diff --git a/org.springframework.core/src/test/java/org/springframework/core/convert/support/CollectionToCollectionConverterTests.java b/org.springframework.core/src/test/java/org/springframework/core/convert/support/CollectionToCollectionConverterTests.java
@@ -24,6 +24,7 @@
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
+import java.util.Collections;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Vector;
@@ -284,6 +285,15 @@ public void convertNonEmptyVector_shouldReturnNonEmptyArrayList() {
 		testCollectionConversionToArrayList(vector);
 	}
 
+	@Test
+	public void testCollectionsEmptyList() throws Exception {
+		CollectionToCollectionConverter converter = new CollectionToCollectionConverter(new GenericConversionService());
+		TypeDescriptor type = new TypeDescriptor(getClass().getField("list"));
+		converter.convert(list, type, TypeDescriptor.valueOf(Class.forName("java.util.Collections$EmptyList")));
+	}
+
+	public List list = Collections.emptyList();
+
 	@SuppressWarnings("rawtypes")
 	private void testCollectionConversionToArrayList(Collection<String> aSource) {
 		Object myConverted = (new CollectionToCollectionConverter(new GenericConversionService())).convert(
