/*
* Copyright 2002-2008 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;
import java.lang.reflect.GenericArrayType;
import java.lang.reflect.Method;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.lang.reflect.TypeVariable;
import java.lang.ref.WeakReference;
import java.lang.ref.Reference;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.WeakHashMap;
import org.springframework.util.Assert;
/**
* Helper class for resolving generic types against type variables.
*
* <p>Mainly intended for usage within the framework, resolving method
* parameter types even when they are declared generically.
*
* <p>Only usable on Java 5. Use an appropriate JdkVersion check before
* calling this class, if a fallback for JDK 1.4 is desirable.
*
* @author Juergen Hoeller
* @author Rob Harrop
* @since 2.5.2
* @see GenericCollectionTypeResolver
* @see JdkVersion
*/
public abstract class GenericTypeResolver {
/** Cache from Class to TypeVariable Map */
private static final Map typeVariableCache = Collections.synchronizedMap(new WeakHashMap());
/**
* Determine the target type for the given parameter specification.
* @param methodParam the method parameter specification
* @return the corresponding generic parameter type
*/
public static Type getTargetType(MethodParameter methodParam) {
Assert.notNull(methodParam, "MethodParameter must not be null");
if (methodParam.getConstructor() != null) {
return methodParam.getConstructor().getGenericParameterTypes()[methodParam.getParameterIndex()];
}
else {
if (methodParam.getParameterIndex() >= 0) {
return methodParam.getMethod().getGenericParameterTypes()[methodParam.getParameterIndex()];
}
else {
return methodParam.getMethod().getGenericReturnType();
}
}
}
/**
* Determine the target type for the given generic parameter type.
* @param methodParam the method parameter specification
* @param clazz the class to resolve type variables against
* @return the corresponding generic parameter or return type
*/
public static Class resolveParameterType(MethodParameter methodParam, Class clazz) {
Type genericType = getTargetType(methodParam);
Assert.notNull(clazz, "Class must not be null");
Map typeVariableMap = getTypeVariableMap(clazz);
Type rawType = getRawType(genericType, typeVariableMap);
Class result = (rawType instanceof Class ? (Class) rawType : methodParam.getParameterType());
methodParam.setParameterType(result);
methodParam.typeVariableMap = typeVariableMap;
return result;
}
/**
* Determine the target type for the generic return type of the given method.
* @param method the method to introspect
* @param clazz the class to resolve type variables against
* @return the corresponding generic parameter or return type
*/
public static Class resolveReturnType(Method method, Class clazz) {
Assert.notNull(method, "Method must not be null");
Type genericType = method.getGenericReturnType();
Assert.notNull(clazz, "Class must not be null");
Map typeVariableMap = getTypeVariableMap(clazz);
Type rawType = getRawType(genericType, typeVariableMap);
return (rawType instanceof Class ? (Class) rawType : method.getReturnType());
}
/**
* Resolve the specified generic type against the given TypeVariable map.
* @param genericType the generic type to resolve
* @param typeVariableMap the TypeVariable Map to resolved against
* @return the type if it resolves to a Class, or <code>Object.class</code> otherwise
*/
static Class resolveType(Type genericType, Map typeVariableMap) {
Type rawType = getRawType(genericType, typeVariableMap);
return (rawType instanceof Class ? (Class) rawType : Object.class);
}
/**
* Determine the raw type for the given generic parameter type.
* @param genericType the generic type to resolve
* @param typeVariableMap the TypeVariable Map to resolved against
* @return the resolved raw type
*/
static Type getRawType(Type genericType, Map typeVariableMap) {
Type resolvedType = genericType;
if (genericType instanceof TypeVariable) {
TypeVariable tv = (TypeVariable) genericType;
resolvedType = (Type) typeVariableMap.get(tv);
if (resolvedType == null) {
resolvedType = extractBoundForTypeVariable(tv);
}
}
if (resolvedType instanceof ParameterizedType) {
return ((ParameterizedType) resolvedType).getRawType();
}
else {
return resolvedType;
}
}
/**
* Build a mapping of {@link TypeVariable#getName TypeVariable names} to concrete
* {@link Class} for the specified {@link Class}. Searches all super types,
* enclosing types and interfaces.
*/
static Map getTypeVariableMap(Class clazz) {
Reference ref = (Reference) typeVariableCache.get(clazz);
Map typeVariableMap = (Map) (ref != null ? ref.get() : null);
if (typeVariableMap == null) {
typeVariableMap = new HashMap();
// interfaces
extractTypeVariablesFromGenericInterfaces(clazz.getGenericInterfaces(), typeVariableMap);
// super class
Type genericType = clazz.getGenericSuperclass();
Class type = clazz.getSuperclass();
while (type != null && !Object.class.equals(type)) {
if (genericType instanceof ParameterizedType) {
ParameterizedType pt = (ParameterizedType) genericType;
populateTypeMapFromParameterizedType(pt, typeVariableMap);
}
extractTypeVariablesFromGenericInterfaces(type.getGenericInterfaces(), typeVariableMap);
genericType = type.getGenericSuperclass();
type = type.getSuperclass();
}
// enclosing class
type = clazz;
while (type.isMemberClass()) {
genericType = type.getGenericSuperclass();
if (genericType instanceof ParameterizedType) {
ParameterizedType pt = (ParameterizedType) genericType;
populateTypeMapFromParameterizedType(pt, typeVariableMap);
}
type = type.getEnclosingClass();
}
typeVariableCache.put(clazz, new WeakReference(typeVariableMap));
}
return typeVariableMap;
}
/**
* Extracts the bound <code>Type</code> for a given {@link TypeVariable}.
*/
static Type extractBoundForTypeVariable(TypeVariable typeVariable) {
Type[] bounds = typeVariable.getBounds();
if (bounds.length == 0) {
return Object.class;
}
Type bound = bounds[0];
if (bound instanceof TypeVariable) {
bound = extractBoundForTypeVariable((TypeVariable) bound);
}
return bound;
}
private static void extractTypeVariablesFromGenericInterfaces(Type[] genericInterfaces, Map typeVariableMap) {
for (int i = 0; i < genericInterfaces.length; i++) {
Type genericInterface = genericInterfaces[i];
if (genericInterface instanceof ParameterizedType) {
ParameterizedType pt = (ParameterizedType) genericInterface;
populateTypeMapFromParameterizedType(pt, typeVariableMap);
if (pt.getRawType() instanceof Class) {
extractTypeVariablesFromGenericInterfaces(
((Class) pt.getRawType()).getGenericInterfaces(), typeVariableMap);
}
}
else if (genericInterface instanceof Class) {
extractTypeVariablesFromGenericInterfaces(
((Class) genericInterface).getGenericInterfaces(), typeVariableMap);
}
}
}
/**
* Read the {@link TypeVariable TypeVariables} from the supplied {@link ParameterizedType}
* and add mappings corresponding to the {@link TypeVariable#getName TypeVariable name} ->
* concrete type to the supplied {@link Map}.
* <p>Consider this case:
* <pre class="code>
* public interface Foo<S, T> {
* ..
* }
*
* public class FooImpl implements Foo<String, Integer> {
* ..
* }</pre>
* For '<code>FooImpl</code>' the following mappings would be added to the {@link Map}:
* {S=java.lang.String, T=java.lang.Integer}.
*/
private static void populateTypeMapFromParameterizedType(ParameterizedType type, Map typeVariableMap) {
if (type.getRawType() instanceof Class) {
Type[] actualTypeArguments = type.getActualTypeArguments();
TypeVariable[] typeVariables = ((Class) type.getRawType()).getTypeParameters();
for (int i = 0; i < actualTypeArguments.length; i++) {
Type actualTypeArgument = actualTypeArguments[i];
TypeVariable variable = typeVariables[i];
if (actualTypeArgument instanceof Class) {
typeVariableMap.put(variable, actualTypeArgument);
}
else if (actualTypeArgument instanceof GenericArrayType) {
typeVariableMap.put(variable, actualTypeArgument);
}
else if (actualTypeArgument instanceof ParameterizedType) {
typeVariableMap.put(variable, actualTypeArgument);
}
else if (actualTypeArgument instanceof TypeVariable) {
// We have a type that is parameterized at instantiation time
// the nearest match on the bridge method will be the bounded type.
TypeVariable typeVariableArgument = (TypeVariable) actualTypeArgument;
Type resolvedType = (Type) typeVariableMap.get(typeVariableArgument);
if (resolvedType == null) {
resolvedType = extractBoundForTypeVariable(typeVariableArgument);
}
typeVariableMap.put(variable, resolvedType);
}
}
}
}
}