SPR-8714 Do not create copy in map-to-map and collection-to-collection conversion if not necessary

Author: rstoyanchev

org.springframework.core/src/main/java/org/springframework/core/convert/support/CollectionToCollectionConverter.java

@@ -57,6 +57,7 @@ public Object convert(Object source, TypeDescriptor sourceType, TypeDescriptor t
 		if (source == null) {
 			return null;
 		}
+		boolean isCopyRequired = !targetType.getType().isInstance(source);
 		Collection<?> sourceCollection = (Collection<?>) source;
 		Collection<Object> target = CollectionFactory.createCollection(targetType.getType(), sourceCollection.size());
 		if (targetType.getElementTypeDescriptor() == null) {
@@ -68,9 +69,12 @@ public Object convert(Object source, TypeDescriptor sourceType, TypeDescriptor t
 			for (Object sourceElement : sourceCollection) {
 				Object targetElement = this.conversionService.convert(sourceElement, sourceType.elementTypeDescriptor(sourceElement), targetType.getElementTypeDescriptor());
 				target.add(targetElement);
+				if (sourceElement != targetElement) {
+					isCopyRequired = true;
+				}
 			}
 		}
-		return target;
+		return isCopyRequired ? target : source;
 	}
 
 }

org.springframework.core/src/main/java/org/springframework/core/convert/support/MapToMapConverter.java

@@ -57,6 +57,7 @@ public Object convert(Object source, TypeDescriptor sourceType, TypeDescriptor t
 		if (source == null) {
 			return null;
 		}
+		boolean isCopyRequired = !targetType.getType().isInstance(source);
 		Map<Object, Object> sourceMap = (Map<Object, Object>) source;
 		Map<Object, Object> targetMap = CollectionFactory.createMap(targetType.getType(), sourceMap.size());
 		for (Map.Entry<Object, Object> entry : sourceMap.entrySet()) {
@@ -65,8 +66,11 @@ public Object convert(Object source, TypeDescriptor sourceType, TypeDescriptor t
 			Object targetKey = convertKey(sourceKey, sourceType, targetType.getMapKeyTypeDescriptor());
 			Object targetValue = convertValue(sourceValue, sourceType, targetType.getMapValueTypeDescriptor());
 			targetMap.put(targetKey, targetValue);
+			if (sourceKey != targetKey || sourceValue != targetValue) {
+				isCopyRequired = true;
+			}
 		}
-		return targetMap;
+		return isCopyRequired ? targetMap : sourceMap;
 	}
 
 	// internal helpers

org.springframework.core/src/test/java/org/springframework/core/convert/support/CollectionToCollectionConverterTests.java

@@ -112,7 +112,7 @@ public void collectionToObjectInteraction() throws Exception {
 		list.add(Arrays.asList("37", "23"));
 		conversionService.addConverter(new CollectionToObjectConverter(conversionService));
 		assertTrue(conversionService.canConvert(List.class, List.class));
-		assertEquals(list, conversionService.convert(list, List.class));
+		assertSame(list, conversionService.convert(list, List.class));
 	}
 
 	@Test
@@ -175,7 +175,7 @@ public void differentImpls() throws Exception {
 		resources.add(new FileSystemResource("test"));
 		resources.add(new TestResource());
 		TypeDescriptor sourceType = TypeDescriptor.forObject(resources);
-		assertEquals(resources, conversionService.convert(resources, sourceType, new TypeDescriptor(getClass().getField("resources"))));
+		assertSame(resources, conversionService.convert(resources, sourceType, new TypeDescriptor(getClass().getField("resources"))));
 	}
 
 	@Test
@@ -186,7 +186,7 @@ public void mixedInNulls() throws Exception {
 		resources.add(new FileSystemResource("test"));
 		resources.add(new TestResource());
 		TypeDescriptor sourceType = TypeDescriptor.forObject(resources);
-		assertEquals(resources, conversionService.convert(resources, sourceType, new TypeDescriptor(getClass().getField("resources"))));
+		assertSame(resources, conversionService.convert(resources, sourceType, new TypeDescriptor(getClass().getField("resources"))));
 	}
 
 	@Test
@@ -195,7 +195,7 @@ public void allNulls() throws Exception {
 		resources.add(null);
 		resources.add(null);
 		TypeDescriptor sourceType = TypeDescriptor.forObject(resources);
-		assertEquals(resources, conversionService.convert(resources, sourceType, new TypeDescriptor(getClass().getField("resources"))));
+		assertSame(resources, conversionService.convert(resources, sourceType, new TypeDescriptor(getClass().getField("resources"))));
 	}
 
 	@Test(expected=ConverterNotFoundException.class)

org.springframework.core/src/test/java/org/springframework/core/convert/support/MapToMapConverterTests.java

@@ -2,6 +2,7 @@
 
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertSame;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
 
@@ -56,7 +57,7 @@ public void scalarMapNotGenericTarget() throws Exception {
 		map.put("1", "9");
 		map.put("2", "37");
 		assertTrue(conversionService.canConvert(Map.class, Map.class));
-		assertEquals(map, conversionService.convert(map, Map.class));
+		assertSame(map, conversionService.convert(map, Map.class));
 	}
 
 	@Test
@@ -140,7 +141,7 @@ public void collectionMapNotGenericTarget() throws Exception {
 		map.put("1", Arrays.asList("9", "12"));
 		map.put("2", Arrays.asList("37", "23"));
 		assertTrue(conversionService.canConvert(Map.class, Map.class));
-		assertEquals(map, conversionService.convert(map, Map.class));
+		assertSame(map, conversionService.convert(map, Map.class));
 	}
 
 	@Test
@@ -151,7 +152,7 @@ public void collectionMapNotGenericTargetCollectionToObjectInteraction() throws
 		conversionService.addConverter(new CollectionToCollectionConverter(conversionService));
 		conversionService.addConverter(new CollectionToObjectConverter(conversionService));
 		assertTrue(conversionService.canConvert(Map.class, Map.class));
-		assertEquals(map, conversionService.convert(map, Map.class));
+		assertSame(map, conversionService.convert(map, Map.class));
 	}
 
 	@Test
@@ -160,7 +161,7 @@ public void emptyMap() throws Exception {
 		TypeDescriptor sourceType = TypeDescriptor.forObject(map);
 		TypeDescriptor targetType = new TypeDescriptor(getClass().getField("emptyMapTarget"));
 		assertTrue(conversionService.canConvert(sourceType, targetType));
-		assertEquals(map, conversionService.convert(map, sourceType, targetType));
+		assertSame(map, conversionService.convert(map, sourceType, targetType));
 	}
 
 	public Map<String, String> emptyMapTarget;
@@ -169,7 +170,7 @@ public void emptyMap() throws Exception {
 	public void emptyMapNoTargetGenericInfo() throws Exception {
 		Map<String, String> map = new HashMap<String, String>();
 		assertTrue(conversionService.canConvert(Map.class, Map.class));
-		assertEquals(map, conversionService.convert(map, Map.class));
+		assertSame(map, conversionService.convert(map, Map.class));
 	}
 
 	@Test
@@ -185,5 +186,5 @@ public void emptyMapDifferentTargetImplType() throws Exception {
 	}
 
 	public LinkedHashMap<String, String> emptyMapDifferentTarget;
-	
+
 }