From e0d922d35202fdb9f309f2aeccd8293b09943ebd Mon Sep 17 00:00:00 2001
From: Juergen Hoeller <jhoeller@vmware.com>
Date: Tue, 6 Dec 2011 21:17:25 +0000
Subject: [PATCH] ConversionService is able to work with
 "Collections.emptyList()" as target type (again; SPR-7293)

---
 .../support/CollectionToCollectionConverter.java       |  3 +++
 .../core/convert/support/MapToMapConverter.java        |  3 +++
 .../support/CollectionToCollectionConverterTests.java  | 10 ++++++++++
 3 files changed, 16 insertions(+)

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
index 74eb7603795..42ad1e8c398 100644
--- 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 @@ final class CollectionToCollectionConverter implements ConditionalGenericConvert
 		}
 		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
index 6652fc84333..e8923e3ec6e 100644
--- 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 @@ final class MapToMapConverter implements ConditionalGenericConverter {
 		}
 		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
index a69f19f0bca..20e6a5f9d7a 100644
--- 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.net.URL;
 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;
@@ -289,6 +290,15 @@ public class CollectionToCollectionConverterTests {
 		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(