introspect element type in case of incoming Collection/Map in order to not accidentally say canConvert=true (SPR-6564)

org.springframework.core/src/main/java/org/springframework/core/convert/TypeDescriptor.java

@@ -47,6 +47,8 @@ public class TypeDescriptor {
 	public static final TypeDescriptor STRING = TypeDescriptor.valueOf(String.class);
 
 
+	private Object value;
+
 	private Class<?> type;
 
 	private TypeDescriptor elementType;
@@ -58,10 +60,22 @@ public class TypeDescriptor {
 	private Annotation[] cachedFieldAnnotations;
 
 
+	/**
+	 * Create a new descriptor for the type of the given value.
+	 * <p>Use this constructor when a conversion point comes from a source such as a Map or
+	 * Collection, where no additional context is available but elements can be introspected.
+	 * @param type the actual type to wrap
+	 */
+	public TypeDescriptor(Object value) {
+		Assert.notNull(value, "Value must not be null");
+		this.value = value;
+		this.type = value.getClass();
+	}
+
 	/**
 	 * Create a new descriptor for the given type.
-	 * <p>Use this constructor when a conversion point comes from a source such as a Map
-	 * or Collection, where no additional context is available.
+	 * <p>Use this constructor when a conversion point comes from a plain source type,
+	 * where no additional context is available.
 	 * @param type the actual type to wrap
 	 */
 	public TypeDescriptor(Class<?> type) {
@@ -242,6 +256,7 @@ public class TypeDescriptor {
 	 * Determine the generic key type of the wrapped Map parameter/field, if any.
 	 * @return the generic type, or <code>null</code> if none
 	 */
+	@SuppressWarnings("unchecked")
 	public Class<?> getMapKeyType() {
 		if (this.field != null) {
 			return GenericCollectionTypeResolver.getMapKeyFieldType(field);
@@ -249,6 +264,18 @@ public class TypeDescriptor {
 		else if (this.methodParameter != null) {
 			return GenericCollectionTypeResolver.getMapKeyParameterType(this.methodParameter);
 		}
+		else if (this.value instanceof Map) {
+			Map map = (Map) this.value;
+			if (!map.isEmpty()) {
+				Object key = map.keySet().iterator().next();
+				if (key != null) {
+					return key.getClass();
+				}
+			}
+		}
+		if (this.type != null) {
+			return GenericCollectionTypeResolver.getMapKeyType((Class<? extends Map>) this.type);
+		}
 		else {
 			return null;
 		}
@@ -258,6 +285,7 @@ public class TypeDescriptor {
 	 * Determine the generic value type of the wrapped Map parameter/field, if any.
 	 * @return the generic type, or <code>null</code> if none
 	 */
+	@SuppressWarnings("unchecked")
 	public Class<?> getMapValueType() {
 		if (this.field != null) {
 			return GenericCollectionTypeResolver.getMapValueFieldType(this.field);
@@ -265,6 +293,18 @@ public class TypeDescriptor {
 		else if (this.methodParameter != null) {
 			return GenericCollectionTypeResolver.getMapValueParameterType(this.methodParameter);
 		}
+		else if (this.value instanceof Map) {
+			Map map = (Map) this.value;
+			if (!map.isEmpty()) {
+				Object val = map.values().iterator().next();
+				if (val != null) {
+					return val.getClass();
+				}
+			}
+		}
+		if (this.type != null) {
+			return GenericCollectionTypeResolver.getMapValueType((Class<? extends Map>) this.type);
+		}
 		else {
 			return null;
 		}
@@ -349,14 +389,26 @@ public class TypeDescriptor {
 
 	@SuppressWarnings("unchecked")
 	private Class<?> getCollectionElementType() {
+		if (this.field != null) {
+			return GenericCollectionTypeResolver.getCollectionFieldType(this.field);
+		}
+		else if (this.methodParameter != null) {
+			return GenericCollectionTypeResolver.getCollectionParameterType(this.methodParameter);
+		}
+		else if (this.value instanceof Collection) {
+			Collection coll = (Collection) this.value;
+			if (!coll.isEmpty()) {
+				Object elem = coll.iterator().next();
+				if (elem != null) {
+					return elem.getClass();
+				}
+			}
+		}
 		if (this.type != null) {
 			return GenericCollectionTypeResolver.getCollectionType((Class<? extends Collection>) this.type);
 		}
-		else if (this.field != null) {
-			return GenericCollectionTypeResolver.getCollectionFieldType(this.field);
-		}
 		else {
-			return GenericCollectionTypeResolver.getCollectionParameterType(this.methodParameter);
+			return null;
 		}
 	}
 

org.springframework.core/src/test/java/org/springframework/core/io/support/ResourceArrayPropertyEditorTests.java

@@ -1,15 +1,33 @@
+/*
+ * Copyright 2002-2006 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
 package org.springframework.core.io.support;
 
 import static org.junit.Assert.*;
-
 import org.junit.Test;
+
 import org.springframework.core.io.Resource;
 
-
+/**
+ * @author Dave Syer
+ */
 public class ResourceArrayPropertyEditorTests {
-	
+
 	private ResourceArrayPropertyEditor editor = new ResourceArrayPropertyEditor();
-	
+
 	@Test
 	public void testVanillaResource() throws Exception {
 		editor.setAsText("classpath:org/springframework/core/io/support/ResourceArrayPropertyEditor.class");