added initial support for handling unknown nested type values when converting collections; now favor factory method for constructing nested type descriptors for clarity (made constructor private); improved javadoc

git-svn-id: https://src.springframework.org/svn/spring-framework/trunk@3867 50f2f4bb-b051-0410-bef5-90022cba6387

org.springframework.beans/src/main/java/org/springframework/beans/BeanWrapperImpl.java

@@ -367,12 +367,11 @@ public class BeanWrapperImpl extends AbstractPropertyAccessor implements BeanWra
 			String actualPropertyName = PropertyAccessorUtils.getPropertyName(propertyName);
 			PropertyDescriptor pd = getPropertyDescriptorInternal(actualPropertyName);
 			if (pd != null) {
-				Class type = getPropertyType(propertyName);
 				if (pd.getReadMethod() != null) {
-					return new PropertyTypeDescriptor(type, new MethodParameter(pd.getReadMethod(), -1), pd);
+					return new PropertyTypeDescriptor(new MethodParameter(pd.getReadMethod(), -1), pd);
 				}
 				else if (pd.getWriteMethod() != null) {
-					return new PropertyTypeDescriptor(type, BeanUtils.getWriteMethodParameter(pd), pd);
+					return new PropertyTypeDescriptor(BeanUtils.getWriteMethodParameter(pd), pd);
 				}
 			}
 		}
@@ -935,10 +934,8 @@ public class BeanWrapperImpl extends AbstractPropertyAccessor implements BeanWra
 					if (isExtractOldValueForEditor()) {
 						oldValue = Array.get(propValue, arrayIndex);
 					}
-					MethodParameter methodParameter = new MethodParameter(pd.getReadMethod(), -1);
-					methodParameter.increaseNestingLevel();					
 					Object convertedValue = convertIfNecessary(propertyName, oldValue, pv.getValue(), requiredType,
-							new PropertyTypeDescriptor(requiredType, methodParameter, pd));
+							PropertyTypeDescriptor.forNestedType(requiredType, new MethodParameter(pd.getReadMethod(), -1), pd));
 					Array.set(propValue, arrayIndex, convertedValue);
 				}
 				catch (IndexOutOfBoundsException ex) {
@@ -956,10 +953,8 @@ public class BeanWrapperImpl extends AbstractPropertyAccessor implements BeanWra
 				if (isExtractOldValueForEditor() && index < list.size()) {
 					oldValue = list.get(index);
 				}
-				MethodParameter methodParameter = new MethodParameter(pd.getReadMethod(), -1);
-				methodParameter.increaseNestingLevel();
 				Object convertedValue = convertIfNecessary(propertyName, oldValue, pv.getValue(), requiredType,
-						new PropertyTypeDescriptor(requiredType, methodParameter, pd));
+						PropertyTypeDescriptor.forNestedType(requiredType, new MethodParameter(pd.getReadMethod(), -1), pd));
 				if (index < list.size()) {
 					list.set(index, convertedValue);
 				}
@@ -995,11 +990,9 @@ public class BeanWrapperImpl extends AbstractPropertyAccessor implements BeanWra
 				}
 				// Pass full property name and old value in here, since we want full
 				// conversion ability for map values.
-				MethodParameter methodParameter = new MethodParameter(pd.getReadMethod(), -1);
-				methodParameter.increaseNestingLevel();
 				Object convertedMapValue = convertIfNecessary(
 						propertyName, oldValue, pv.getValue(), mapValueType,
-						new PropertyTypeDescriptor(mapValueType, methodParameter, pd));
+						PropertyTypeDescriptor.forNestedType(mapValueType, new MethodParameter(pd.getReadMethod(), -1), pd));
 				map.put(convertedMapKey, convertedMapValue);
 			}
 			else {

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

@@ -86,8 +86,7 @@ public class TypeDescriptor {
 
 	/**
 	 * Create a new type descriptor from a method or constructor parameter.
-	 * <p>Use this constructor when a target conversion point originates from a method parameter,
-	 * such as a setter method argument.
+	 * Use this constructor when a target conversion point originates from a method parameter, such as a setter method argument.
 	 * @param methodParameter the MethodParameter to wrap
 	 */
 	public TypeDescriptor(MethodParameter methodParameter) {
@@ -106,24 +105,17 @@ public class TypeDescriptor {
 		this.type = field.getType();
 		this.field = field;
 	}
-
-	/**
-	 * Create a new type descriptor for the given class.
-	 * @param type the class
-	 * @return the type descriptor
-	 */
-	public static TypeDescriptor valueOf(Class<?> type) {
-		if (type == null) {
-			return NULL;
-		}
-		TypeDescriptor desc = typeDescriptorCache.get(type);
-		return (desc != null ? desc : new TypeDescriptor(type));
-	}
 	
 	/**
-	 * Create a new type descriptor for the class of the given object.
-	 * @param object the object
+	 * Create a new type descriptor for object.
+	 * Use this factory method to introspect a source object's type before asking the conversion system to convert it to some another type.
+	 * If the object is null, returns {@link TypeDescriptor#NULL}.
+	 * If the object is not a collection, simply calls {@link #valueOf(Class)}.
+	 * If the object is a collection, this factory method will derive the element type(s) by introspecting the collection.
+	 * @param object the source object
 	 * @return the type descriptor
+	 * @see ConversionService#convert(Object, Class)
+	 * @see CollectionUtils#findCommonElementType(Collection)
 	 */
 	public static TypeDescriptor forObject(Object object) {
 		if (object == null) {
@@ -139,6 +131,32 @@ public class TypeDescriptor {
 			return valueOf(object.getClass());
 		}
 	}
+
+	/**
+	 * Create a new type descriptor for a nested type declared on an array, collection, or map-based method parameter.
+	 * Use this factory method when you've resolved a nested source object such as a collection element or map value and wish to have it converted.
+	 * @param nestedType the nested type
+	 * @param parentMethodParameter the parent method parameter declaring the collection or map
+	 * @return the nested type descriptor
+	 */
+	public static TypeDescriptor forNestedType(Class<?> nestedType, MethodParameter parentMethodParameter) {
+		return new TypeDescriptor(nestedType, parentMethodParameter);
+	}
+	
+	/**
+	 * Create a new type descriptor for the given class.
+	 * Use this to instruct the conversion system to convert to an object to a specific target type, when no type location such as a method parameter or field is available.
+	 * Generally prefer use of {@link #forObject(Object)} for constructing source type descriptors for source objects.
+	 * @param type the class
+	 * @return the type descriptor
+	 */
+	public static TypeDescriptor valueOf(Class<?> type) {
+		if (type == null) {
+			return NULL;
+		}
+		TypeDescriptor desc = typeDescriptorCache.get(type);
+		return (desc != null ? desc : new TypeDescriptor(type));
+	}
 	
 	/**
 	 * Determine the declared (non-generic) type of the wrapped parameter/field.
@@ -309,17 +327,6 @@ public class TypeDescriptor {
 
 	// special case public operations
 
-	/**
-	 * Constructs a new TypeDescriptor for a nested type declared within a method parameter, such as a collection type or map key or value type.
-	 */
-	public TypeDescriptor(Class<?> nestedType, MethodParameter methodParameter) {
-		if (nestedType == null) {
-			nestedType = Object.class;
-		}
-		this.type = nestedType;
-		this.methodParameter = methodParameter;
-	}
-	
 	/**
 	 * Exposes the underlying MethodParameter providing context for this TypeDescriptor.
 	 * Used to support legacy code scenarios where callers are already using the MethodParameter API (BeanWrapper).
@@ -402,6 +409,11 @@ public class TypeDescriptor {
 	}
 
 	// subclassing hooks
+
+	protected TypeDescriptor(Class<?> nestedType, MethodParameter parentMethodParameter) {
+		this.type = handleUnknownNestedType(nestedType);
+		this.methodParameter = createNestedMethodParameter(parentMethodParameter);
+	}
 	
 	protected Annotation[] resolveAnnotations() {
 		if (this.field != null) {
@@ -446,13 +458,9 @@ public class TypeDescriptor {
 	}
 
 	private TypeDescriptor createNestedTypeDescriptor(Class<?> nestedType) {
-		if (nestedType == null) {
-			nestedType = Object.class;
-		}
+		nestedType = handleUnknownNestedType(nestedType);
 		if (this.methodParameter != null) {
-			MethodParameter nested = new MethodParameter(this.methodParameter);
-			nested.increaseNestingLevel();
-			return newNestedTypeDescriptor(nestedType, nested);				
+			return newNestedTypeDescriptor(nestedType, createNestedMethodParameter(this.methodParameter));				
 		}
 		else if (this.field != null) {
 			return new TypeDescriptor(nestedType, this.field, this.fieldNestingLevel + 1);
@@ -461,7 +469,7 @@ public class TypeDescriptor {
 			return TypeDescriptor.valueOf(nestedType);
 		}
 	}
-
+	
 	private Class<?> resolveCollectionElementType() {
 		if (this.methodParameter != null) {
 			return GenericCollectionTypeResolver.getCollectionParameterType(this.methodParameter);
@@ -498,13 +506,17 @@ public class TypeDescriptor {
 		}
 	}
 
-	// internal constructors
+	private Class<?> handleUnknownNestedType(Class<?> nestedType) {
+		return nestedType != null ? nestedType : Object.class;
+	}
 
-	private TypeDescriptor(Class<?> nestedType, Field field, int nestingLevel) {
-		this.type = nestedType;
-		this.field = field;
-		this.fieldNestingLevel = nestingLevel;
+	private MethodParameter createNestedMethodParameter(MethodParameter parentMethodParameter) {
+		MethodParameter methodParameter = new MethodParameter(parentMethodParameter);
+		methodParameter.increaseNestingLevel();
+		return methodParameter;
 	}
+	
+	// internal constructors
 
 	private TypeDescriptor() {
 	}
@@ -534,4 +546,10 @@ public class TypeDescriptor {
 		this.mapValueType = TypeDescriptor.valueOf(valueType);
 	}
 
+	private TypeDescriptor(Class<?> nestedType, Field field, int nestingLevel) {
+		this.type = nestedType;
+		this.field = field;
+		this.fieldNestingLevel = nestingLevel;
+	}
+
 }

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

@@ -49,7 +49,12 @@ final class CollectionToCollectionConverter implements ConditionalGenericConvert
 	}
 
 	public boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType) {
-		return this.conversionService.canConvert(sourceType.getElementTypeDescriptor(), targetType.getElementTypeDescriptor());
+		TypeDescriptor sourceElementType = sourceType.getElementTypeDescriptor();
+		TypeDescriptor targetElementType = targetType.getElementTypeDescriptor();
+		if (Object.class.equals(sourceElementType.getType()) || Object.class.equals(targetElementType.getType())) {
+			return true;
+		}
+		return this.conversionService.canConvert(sourceElementType, targetElementType);
 	}
 	
 	public Object convert(Object source, TypeDescriptor sourceType, TypeDescriptor targetType) {

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

@@ -173,7 +173,7 @@ public class GenericConversionService implements ConversionService, ConverterReg
 		Assert.isTrue(source == null || sourceType.getObjectType().isInstance(source));
 		GenericConverter converter = getConverter(sourceType, targetType);
 		if (converter == null) {
-			if (source == null || targetType.getObjectType().isInstance(source)) {
+			if (source == null || sourceType.isAssignableTo(targetType)) {
 				logger.debug("No converter found - returning assignable source object as-is");
 				return source;
 			}

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

@@ -34,6 +34,7 @@ import org.springframework.util.StringUtils;
  * (getter/setter) and on the underlying field, if found.
  *
  * @author Juergen Hoeller
+ * @author Keith Donald
  * @since 3.0.2
  */
 public class PropertyTypeDescriptor extends TypeDescriptor {
@@ -41,18 +42,24 @@ public class PropertyTypeDescriptor extends TypeDescriptor {
 	private final PropertyDescriptor propertyDescriptor;
 
 	/**
-	 * Create a new BeanTypeDescriptor for the given bean property.
-	 * @param propertyDescriptor the corresponding JavaBean PropertyDescriptor
+	 * Create a new type descriptor for the given bean property.
 	 * @param methodParameter the target method parameter
+	 * @param propertyDescriptor the corresponding JavaBean PropertyDescriptor
 	 */
 	public PropertyTypeDescriptor(MethodParameter methodParameter, PropertyDescriptor propertyDescriptor) {
 		super(methodParameter);
 		this.propertyDescriptor = propertyDescriptor;
 	}
-	
-	public PropertyTypeDescriptor(Class<?> type, MethodParameter methodParameter, PropertyDescriptor propertyDescriptor) {
-		super(type, methodParameter);
-		this.propertyDescriptor = propertyDescriptor;
+
+	/**
+	 * Create a new type descriptor for a nested type declared on an array, collection, or map-based property.
+	 * Use this factory method when you've resolved a nested source object such as a collection element or map value and wish to have it converted.
+	 * @param nestedType the nested type
+	 * @param parentMethodParameter the parent property's method parameter that declares the collection or map
+	 * @return the parent property descriptor
+	 */
+	public static PropertyTypeDescriptor forNestedType(Class<?> nestedType, MethodParameter propertyMethodParameter, PropertyDescriptor propertyDescriptor) {
+		return new PropertyTypeDescriptor(nestedType, propertyMethodParameter, propertyDescriptor);
 	}
 
 	/**
@@ -102,8 +109,15 @@ public class PropertyTypeDescriptor extends TypeDescriptor {
 		return annMap.values().toArray(new Annotation[annMap.size()]);
 	}
 
-	public TypeDescriptor newNestedTypeDescriptor(Class<?> nestedType, MethodParameter nested) {
+	protected TypeDescriptor newNestedTypeDescriptor(Class<?> nestedType, MethodParameter nested) {
 		return new PropertyTypeDescriptor(nestedType, nested, this.propertyDescriptor);
 	}
 
+	// internal constructors
+	
+	private PropertyTypeDescriptor(Class<?> nestedType, MethodParameter methodParameter, PropertyDescriptor propertyDescriptor) {
+		super(nestedType, methodParameter);
+		this.propertyDescriptor = propertyDescriptor;
+	}
+
 }

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

@@ -382,6 +382,19 @@ public class GenericConversionServiceTests {
 	public static Map<String, Integer> map;
 
 
+	@Test
+	public void emptyList() throws Exception {
+		conversionService.addConverter(new CollectionToCollectionConverter(conversionService));
+		conversionService.addConverterFactory(new StringToNumberConverterFactory());
+		List<String> list = new ArrayList<String>();
+		TypeDescriptor sourceType = TypeDescriptor.forObject(list);
+		TypeDescriptor targetType = new TypeDescriptor(getClass().getField("emptyListTarget"));
+		assertTrue(conversionService.canConvert(sourceType, targetType));
+		assertEquals(list, conversionService.convert(list, sourceType, targetType));
+	}
+
+	public List<Integer> emptyListTarget;
+	
 	private interface MyBaseInterface {
 
 	}

org.springframework.expression/src/main/java/org/springframework/expression/spel/support/ReflectionHelper.java

@@ -236,7 +236,7 @@ public class ReflectionHelper {
 			TypeDescriptor targetType;
 			if (varargsPosition != null && argPosition >= varargsPosition) {
 				MethodParameter methodParam = MethodParameter.forMethodOrConstructor(methodOrCtor, varargsPosition);
-				targetType = new TypeDescriptor(methodParam.getParameterType().getComponentType(), methodParam);
+				targetType = TypeDescriptor.forNestedType(methodParam.getParameterType().getComponentType(), methodParam);
 			}
 			else {
 				targetType = new TypeDescriptor(MethodParameter.forMethodOrConstructor(methodOrCtor, argPosition));
@@ -268,7 +268,7 @@ public class ReflectionHelper {
 			TypeDescriptor targetType;
 			if (varargsPosition != null && argPosition >= varargsPosition) {
 				MethodParameter methodParam = new MethodParameter(method, varargsPosition);
-				targetType = new TypeDescriptor(methodParam.getParameterType().getComponentType(), methodParam);
+				targetType = TypeDescriptor.forNestedType(methodParam.getParameterType().getComponentType(), methodParam);
 			}
 			else {
 				targetType = new TypeDescriptor(new MethodParameter(method, argPosition));