org.springframework.core.GenericTypeResolver Maven / Gradle / Ivy
/*
* Copyright 2002-2010 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.ref.Reference;
import java.lang.ref.WeakReference;
import java.lang.reflect.Array;
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.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.
*
* Mainly intended for usage within the framework, resolving method
* parameter types even when they are declared generically.
*
* @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 single type argument of the given generic interface against
* the given target class which is assumed to implement the generic interface
* and possibly declare a concrete type for its type variable.
* @param clazz the target class to check against
* @param genericIfc the generic interface or superclass to resolve the type argument from
* @return the resolved type of the argument, or null if not resolvable
*/
public static Class resolveTypeArgument(Class clazz, Class genericIfc) {
Class[] typeArgs = resolveTypeArguments(clazz, genericIfc);
if (typeArgs == null) {
return null;
}
if (typeArgs.length != 1) {
throw new IllegalArgumentException("Expected 1 type argument on generic interface [" +
genericIfc.getName() + "] but found " + typeArgs.length);
}
return typeArgs[0];
}
/**
* Resolve the type arguments of the given generic interface against the given
* target class which is assumed to implement the generic interface and possibly
* declare concrete types for its type variables.
* @param clazz the target class to check against
* @param genericIfc the generic interface or superclass to resolve the type argument from
* @return the resolved type of each argument, with the array size matching the
* number of actual type arguments, or null if not resolvable
*/
public static Class[] resolveTypeArguments(Class clazz, Class genericIfc) {
return doResolveTypeArguments(clazz, clazz, genericIfc);
}
private static Class[] doResolveTypeArguments(Class ownerClass, Class classToIntrospect, Class genericIfc) {
while (classToIntrospect != null) {
if (genericIfc.isInterface()) {
Type[] ifcs = classToIntrospect.getGenericInterfaces();
for (Type ifc : ifcs) {
Class[] result = doResolveTypeArguments(ownerClass, ifc, genericIfc);
if (result != null) {
return result;
}
}
}
else {
Class[] result = doResolveTypeArguments(
ownerClass, classToIntrospect.getGenericSuperclass(), genericIfc);
if (result != null) {
return result;
}
}
classToIntrospect = classToIntrospect.getSuperclass();
}
return null;
}
private static Class[] doResolveTypeArguments(Class ownerClass, Type ifc, Class genericIfc) {
if (ifc instanceof ParameterizedType) {
ParameterizedType paramIfc = (ParameterizedType) ifc;
Type rawType = paramIfc.getRawType();
if (genericIfc.equals(rawType)) {
Type[] typeArgs = paramIfc.getActualTypeArguments();
Class[] result = new Class[typeArgs.length];
for (int i = 0; i < typeArgs.length; i++) {
Type arg = typeArgs[i];
result[i] = extractClass(ownerClass, arg);
}
return result;
}
else if (genericIfc.isAssignableFrom((Class) rawType)) {
return doResolveTypeArguments(ownerClass, (Class) rawType, genericIfc);
}
}
else if (genericIfc.isAssignableFrom((Class) ifc)) {
return doResolveTypeArguments(ownerClass, (Class) ifc, genericIfc);
}
return null;
}
/**
* Extract a class instance from given Type.
*/
private static Class extractClass(Class ownerClass, Type arg) {
if (arg instanceof ParameterizedType) {
return extractClass(ownerClass, ((ParameterizedType) arg).getRawType());
}
else if (arg instanceof GenericArrayType) {
GenericArrayType gat = (GenericArrayType) arg;
Type gt = gat.getGenericComponentType();
Class componentClass = extractClass(ownerClass, gt);
return Array.newInstance(componentClass, 0).getClass();
}
else if (arg instanceof TypeVariable) {
TypeVariable tv = (TypeVariable) arg;
arg = getTypeVariableMap(ownerClass).get(tv);
if (arg == null) {
arg = extractBoundForTypeVariable(tv);
}
else {
arg = extractClass(ownerClass, arg);
}
}
return (arg instanceof Class ? (Class) arg : Object.class);
}
/**
* 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 Object.class 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 = 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 = typeVariableCache.get(clazz);
Map typeVariableMap = (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 Type 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 (Type genericInterface : genericInterfaces) {
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}.
* Consider this case:
*
-->