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

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 @@ package org.springframework.core.convert;
 
 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 @@ class ClassDescriptor extends AbstractDescriptor {
 	}
 
 	@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