Resolve Collection element types during conversion

TypeDescriptor.valueOf now uses GenericCollectionTypeResolver to resolve
Collection and Map element types whereas previously this information was
simply not supported, i.e. null.

Issue: SPR-9257

Author: philwebb

spring-core/src/main/java/org/springframework/core/convert/ClassDescriptor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2011 the original author or authors.
+ * Copyright 2002-2012 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.
@@ -18,8 +18,11 @@
 
 import java.lang.annotation.Annotation;
 
+import org.springframework.core.GenericCollectionTypeResolver;
+
 /**
  * @author Keith Donald
+ * @author Phillip Webb
  * @since 3.1
  */
 class ClassDescriptor extends AbstractDescriptor {
@@ -34,18 +37,21 @@ public Annotation[] getAnnotations() {
 	}
 
 	@Override
+	@SuppressWarnings({ "unchecked", "rawtypes" })
 	protected Class<?> resolveCollectionElementType() {
-		return null;
+		return GenericCollectionTypeResolver.getCollectionType((Class) getType());
 	}
 
 	@Override
+	@SuppressWarnings({ "unchecked", "rawtypes" })
 	protected Class<?> resolveMapKeyType() {
-		return null;
+		return GenericCollectionTypeResolver.getMapKeyType((Class) getType());
 	}
 
 	@Override
+	@SuppressWarnings({ "unchecked", "rawtypes" })
 	protected Class<?> resolveMapValueType() {
-		return null;
+		return GenericCollectionTypeResolver.getMapValueType((Class) getType());
 	}
 
 	@Override

spring-core/src/test/java/org/springframework/core/convert/TypeDescriptorTests.java

@@ -24,6 +24,7 @@
 import java.util.Collection;
 import java.util.Date;
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 
@@ -818,4 +819,26 @@ public void testUpCastNotSuper() throws Exception {
 		}
 	}
 
+	@Test
+	public void elementTypeForCollectionSubclass() throws Exception {
+		@SuppressWarnings("serial")
+		class CustomSet extends HashSet<String> {
+		}
+
+		assertEquals(TypeDescriptor.valueOf(CustomSet.class).getElementTypeDescriptor(), TypeDescriptor.valueOf(String.class));
+		assertEquals(TypeDescriptor.forObject(new CustomSet()).getElementTypeDescriptor(), TypeDescriptor.valueOf(String.class));
+	}
+
+	@Test
+	public void elementTypeForMapSubclass() throws Exception {
+		@SuppressWarnings("serial")
+		class CustomMap extends HashMap<String, Integer> {
+		}
+
+		assertEquals(TypeDescriptor.valueOf(CustomMap.class).getMapKeyTypeDescriptor(), TypeDescriptor.valueOf(String.class));
+		assertEquals(TypeDescriptor.valueOf(CustomMap.class).getMapValueTypeDescriptor(), TypeDescriptor.valueOf(Integer.class));
+		assertEquals(TypeDescriptor.forObject(new CustomMap()).getMapKeyTypeDescriptor(), TypeDescriptor.valueOf(String.class));
+		assertEquals(TypeDescriptor.forObject(new CustomMap()).getMapValueTypeDescriptor(), TypeDescriptor.valueOf(Integer.class));
+	}
+
 }