/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.apache.commons.lang3.reflect;
import java.lang.reflect.Array;
import java.lang.reflect.GenericArrayType;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.lang.reflect.TypeVariable;
import java.lang.reflect.WildcardType;
import java.util.Arrays;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import org.apache.commons.lang3.ClassUtils;
/**
* <p> Utility methods focusing on type inspection, particularly with regard to
* generics. </p>
*
* @since 3.0
* @version $Id: TypeUtils.java 1144929 2011-07-10 18:26:16Z ggregory $
*/
public class TypeUtils {
/**
* <p> TypeUtils instances should NOT be constructed in standard
* programming. Instead, the class should be used as
* <code>TypeUtils.isAssignable(cls, toClass)</code>. </p> <p> This
* constructor is public to permit tools that require a JavaBean instance to
* operate. </p>
*/
public TypeUtils() {
super();
}
/**
* <p> Checks if the subject type may be implicitly cast to the target type
* following the Java generics rules. If both types are {@link Class}
* objects, the method returns the result of
* {@link ClassUtils#isAssignable(Class, Class)}. </p>
*
* @param type the subject type to be assigned to the target type
* @param toType the target type
* @return <code>true</code> if <code>type</code> is assignable to <code>toType</code>.
*/
public static boolean isAssignable(Type type, Type toType) {
return isAssignable(type, toType, null);
}
/**
* <p> Checks if the subject type may be implicitly cast to the target type
* following the Java generics rules. </p>
*
* @param type the subject type to be assigned to the target type
* @param toType the target type
* @param typeVarAssigns optional map of type variable assignments
* @return <code>true</code> if <code>type</code> is assignable to <code>toType</code>.
*/
private static boolean isAssignable(Type type, Type toType,
Map<TypeVariable<?>, Type> typeVarAssigns) {
if (toType == null || toType instanceof Class<?>) {
return isAssignable(type, (Class<?>) toType);
}
if (toType instanceof ParameterizedType) {
return isAssignable(type, (ParameterizedType) toType, typeVarAssigns);
}
if (toType instanceof GenericArrayType) {
return isAssignable(type, (GenericArrayType) toType, typeVarAssigns);
}
if (toType instanceof WildcardType) {
return isAssignable(type, (WildcardType) toType, typeVarAssigns);
}
// *
if (toType instanceof TypeVariable<?>) {
return isAssignable(type, (TypeVariable<?>) toType, typeVarAssigns);
}
// */
throw new IllegalStateException("found an unhandled type: " + toType);
}
/**
* <p> Checks if the subject type may be implicitly cast to the target class
* following the Java generics rules. </p>
*
* @param type the subject type to be assigned to the target type
* @param toClass the target class
* @return true if <code>type</code> is assignable to <code>toClass</code>.
*/
private static boolean isAssignable(Type type, Class<?> toClass) {
if (type == null) {
// consistency with ClassUtils.isAssignable() behavior
return toClass == null || !toClass.isPrimitive();
}
// only a null type can be assigned to null type which
// would have cause the previous to return true
if (toClass == null) {
return false;
}
// all types are assignable to themselves
if (toClass.equals(type)) {
return true;
}
if (type instanceof Class<?>) {
// just comparing two classes
return ClassUtils.isAssignable((Class<?>) type, toClass);
}
if (type instanceof ParameterizedType) {
// only have to compare the raw type to the class
return isAssignable(getRawType((ParameterizedType) type), toClass);
}
// *
if (type instanceof TypeVariable<?>) {
// if any of the bounds are assignable to the class, then the
// type is assignable to the class.
for (Type bound : ((TypeVariable<?>) type).getBounds()) {
if (isAssignable(bound, toClass)) {
return true;
}
}
return false;
}
// the only classes to which a generic array type can be assigned
// are class Object and array classes
if (type instanceof GenericArrayType) {
return toClass.equals(Object.class)
|| toClass.isArray()
&& isAssignable(((GenericArrayType) type).getGenericComponentType(), toClass
.getComponentType());
}
// wildcard types are not assignable to a class (though one would think
// "? super Object" would be assignable to Object)
if (type instanceof WildcardType) {
return false;
}
throw new IllegalStateException("found an unhandled type: " + type);
}
/**
* <p> Checks if the subject type may be implicitly cast to the target
* parameterized type following the Java generics rules. </p>
*
* @param type the subject type to be assigned to the target type
* @param toParameterizedType the target parameterized type
* @param typeVarAssigns a map with type variables
* @return true if <code>type</code> is assignable to <code>toType</code>.
*/
private static boolean isAssignable(Type type, ParameterizedType toParameterizedType,
Map<TypeVariable<?>, Type> typeVarAssigns) {
if (type == null) {
return true;
}
// only a null type can be assigned to null type which
// would have cause the previous to return true
if (toParameterizedType == null) {
return false;
}
// all types are assignable to themselves
if (toParameterizedType.equals(type)) {
return true;
}
// get the target type's raw type
Class<?> toClass = getRawType(toParameterizedType);
// get the subject type's type arguments including owner type arguments
// and supertype arguments up to and including the target class.
Map<TypeVariable<?>, Type> fromTypeVarAssigns = getTypeArguments(type, toClass, null);
// null means the two types are not compatible
if (fromTypeVarAssigns == null) {
return false;
}
// compatible types, but there's no type arguments. this is equivalent
// to comparing Map< ?, ? > to Map, and raw types are always assignable
// to parameterized types.
if (fromTypeVarAssigns.isEmpty()) {
return true;
}
// get the target type's type arguments including owner type arguments
Map<TypeVariable<?>, Type> toTypeVarAssigns = getTypeArguments(toParameterizedType,
toClass, typeVarAssigns);
// now to check each type argument
for (Map.Entry<TypeVariable<?>, Type> entry : toTypeVarAssigns.entrySet()) {
Type toTypeArg = entry.getValue();
Type fromTypeArg = fromTypeVarAssigns.get(entry.getKey());
// parameters must either be absent from the subject type, within
// the bounds of the wildcard type, or be an exact match to the
// parameters of the target type.
if (fromTypeArg != null
&& !toTypeArg.equals(fromTypeArg)
&& !(toTypeArg instanceof WildcardType && isAssignable(fromTypeArg, toTypeArg,
typeVarAssigns))) {
return false;
}
}
return true;
}
/**
* <p> Checks if the subject type may be implicitly cast to the target
* generic array type following the Java generics rules. </p>
*
* @param type the subject type to be assigned to the target type
* @param toGenericArrayType the target generic array type
* @param typeVarAssigns a map with type variables
* @return true if <code>type</code> is assignable to
* <code>toGenericArrayType</code>.
*/
private static boolean isAssignable(Type type, GenericArrayType toGenericArrayType,
Map<TypeVariable<?>, Type> typeVarAssigns) {
if (type == null) {
return true;
}
// only a null type can be assigned to null type which
// would have cause the previous to return true
if (toGenericArrayType == null) {
return false;
}
// all types are assignable to themselves
if (toGenericArrayType.equals(type)) {
return true;
}
Type toComponentType = toGenericArrayType.getGenericComponentType();
if (type instanceof Class<?>) {
Class<?> cls = (Class<?>) type;
// compare the component types
return cls.isArray()
&& isAssignable(cls.getComponentType(), toComponentType, typeVarAssigns);
}
if (type instanceof GenericArrayType) {
// compare the component types
return isAssignable(((GenericArrayType) type).getGenericComponentType(),
toComponentType, typeVarAssigns);
}
if (type instanceof WildcardType) {
// so long as one of the upper bounds is assignable, it's good
for (Type bound : getImplicitUpperBounds((WildcardType) type)) {
if (isAssignable(bound, toGenericArrayType)) {
return true;
}
}
return false;
}
if (type instanceof TypeVariable<?>) {
// probably should remove the following logic and just return false.
// type variables cannot specify arrays as bounds.
for (Type bound : getImplicitBounds((TypeVariable<?>) type)) {
if (isAssignable(bound, toGenericArrayType)) {
return true;
}
}
return false;
}
if (type instanceof ParameterizedType) {
// the raw type of a parameterized type is never an array or
// generic array, otherwise the declaration would look like this:
// Collection[]< ? extends String > collection;
return false;
}
throw new IllegalStateException("found an unhandled type: " + type);
}
/**
* <p> Checks if the subject type may be implicitly cast to the target
* wildcard type following the Java generics rules. </p>
*
* @param type the subject type to be assigned to the target type
* @param toWildcardType the target wildcard type
* @param typeVarAssigns a map with type variables
* @return true if <code>type</code> is assignable to
* <code>toWildcardType</code>.
*/
private static boolean isAssignable(Type type, WildcardType toWildcardType,
Map<TypeVariable<?>, Type> typeVarAssigns) {
if (type == null) {
return true;
}
// only a null type can be assigned to null type which
// would have cause the previous to return true
if (toWildcardType == null) {
return false;
}
// all types are assignable to themselves
if (toWildcardType.equals(type)) {
return true;
}
Type[] toUpperBounds = getImplicitUpperBounds(toWildcardType);
Type[] toLowerBounds = getImplicitLowerBounds(toWildcardType);
if (type instanceof WildcardType) {
WildcardType wildcardType = (WildcardType) type;
Type[] upperBounds = getImplicitUpperBounds(wildcardType);
Type[] lowerBounds = getImplicitLowerBounds(wildcardType);
for (Type toBound : toUpperBounds) {
// if there are assignments for unresolved type variables,
// now's the time to substitute them.
toBound = substituteTypeVariables(toBound, typeVarAssigns);
// each upper bound of the subject type has to be assignable to
// each
// upper bound of the target type
for (Type bound : upperBounds) {
if (!isAssignable(bound, toBound, typeVarAssigns)) {
return false;
}
}
}
for (Type toBound : toLowerBounds) {
// if there are assignments for unresolved type variables,
// now's the time to substitute them.
toBound = substituteTypeVariables(toBound, typeVarAssigns);
// each lower bound of the target type has to be assignable to
// each
// lower bound of the subject type
for (Type bound : lowerBounds) {
if (!isAssignable(toBound, bound, typeVarAssigns)) {
return false;
}
}
}
return true;
}
for (Type toBound : toUpperBounds) {
// if there are assignments for unresolved type variables,
// now's the time to substitute them.
if (!isAssignable(type, substituteTypeVariables(toBound, typeVarAssigns),
typeVarAssigns)) {
return false;
}
}
for (Type toBound : toLowerBounds) {
// if there are assignments for unresolved type variables,
// now's the time to substitute them.
if (!isAssignable(substituteTypeVariables(toBound, typeVarAssigns), type,
typeVarAssigns)) {
return false;
}
}
return true;
}
/**
* <p> Checks if the subject type may be implicitly cast to the target type
* variable following the Java generics rules. </p>
*
* @param type the subject type to be assigned to the target type
* @param toTypeVariable the target type variable
* @param typeVarAssigns a map with type variables
* @return true if <code>type</code> is assignable to
* <code>toTypeVariable</code>.
*/
private static boolean isAssignable(Type type, TypeVariable<?> toTypeVariable,
Map<TypeVariable<?>, Type> typeVarAssigns) {
if (type == null) {
return true;
}
// only a null type can be assigned to null type which
// would have cause the previous to return true
if (toTypeVariable == null) {
return false;
}
// all types are assignable to themselves
if (toTypeVariable.equals(type)) {
return true;
}
if (type instanceof TypeVariable<?>) {
// a type variable is assignable to another type variable, if
// and only if the former is the latter, extends the latter, or
// is otherwise a descendant of the latter.
Type[] bounds = getImplicitBounds((TypeVariable<?>) type);
for (Type bound : bounds) {
if (isAssignable(bound, toTypeVariable, typeVarAssigns)) {
return true;
}
}
}
if (type instanceof Class<?> || type instanceof ParameterizedType
|| type instanceof GenericArrayType || type instanceof WildcardType) {
return false;
}
throw new IllegalStateException("found an unhandled type: " + type);
}
/**
* <p> </p>
*
* @param type the type to be replaced
* @param typeVarAssigns the map with type variables
* @return the replaced type
* @throws IllegalArgumentException if the type cannot be substituted
*/
private static Type substituteTypeVariables(Type type, Map<TypeVariable<?>, Type> typeVarAssigns) {
if (type instanceof TypeVariable<?> && typeVarAssigns != null) {
Type replacementType = typeVarAssigns.get(type);
if (replacementType == null) {
throw new IllegalArgumentException("missing assignment type for type variable "
+ type);
}
return replacementType;
}
return type;
}
/**
* <p> Retrieves all the type arguments for this parameterized type
* including owner hierarchy arguments such as <code>
* Outer<K,V>.Inner<T>.DeepInner<E></code> . The arguments are returned in a
* {@link Map} specifying the argument type for each {@link TypeVariable}.
* </p>
*
* @param type specifies the subject parameterized type from which to
* harvest the parameters.
* @return a map of the type arguments to their respective type variables.
*/
public static Map<TypeVariable<?>, Type> getTypeArguments(ParameterizedType type) {
return getTypeArguments(type, getRawType(type), null);
}
/**
* <p> Gets the type arguments of a class/interface based on a subtype. For
* instance, this method will determine that both of the parameters for the
* interface {@link Map} are {@link Object} for the subtype
* {@link java.util.Properties Properties} even though the subtype does not
* directly implement the <code>Map</code> interface. <p> </p> This method
* returns <code>null</code> if <code>type</code> is not assignable to
* <code>toClass</code>. It returns an empty map if none of the classes or
* interfaces in its inheritance hierarchy specify any type arguments. </p>
* <p> A side-effect of this method is that it also retrieves the type
* arguments for the classes and interfaces that are part of the hierarchy
* between <code>type</code> and <code>toClass</code>. So with the above
* example, this method will also determine that the type arguments for
* {@link java.util.Hashtable Hashtable} are also both <code>Object</code>.
* In cases where the interface specified by <code>toClass</code> is
* (indirectly) implemented more than once (e.g. where <code>toClass</code>
* specifies the interface {@link java.lang.Iterable Iterable} and
* <code>type</code> specifies a parameterized type that implements both
* {@link java.util.Set Set} and {@link java.util.Collection Collection}),
* this method will look at the inheritance hierarchy of only one of the
* implementations/subclasses; the first interface encountered that isn't a
* subinterface to one of the others in the <code>type</code> to
* <code>toClass</code> hierarchy. </p>
*
* @param type the type from which to determine the type parameters of
* <code>toClass</code>
* @param toClass the class whose type parameters are to be determined based
* on the subtype <code>type</code>
* @return a map of the type assignments for the type variables in each type
* in the inheritance hierarchy from <code>type</code> to
* <code>toClass</code> inclusive.
*/
public static Map<TypeVariable<?>, Type> getTypeArguments(Type type, Class<?> toClass) {
return getTypeArguments(type, toClass, null);
}
/**
* <p> Return a map of the type arguments of <code>type</code> in the context of <code>toClass</code>. </p>
*
* @param type the type in question
* @param toClass the class
* @param subtypeVarAssigns a map with type variables
* @return the map with type arguments
*/
private static Map<TypeVariable<?>, Type> getTypeArguments(Type type, Class<?> toClass,
Map<TypeVariable<?>, Type> subtypeVarAssigns) {
if (type instanceof Class<?>) {
return getTypeArguments((Class<?>) type, toClass, subtypeVarAssigns);
}
if (type instanceof ParameterizedType) {
return getTypeArguments((ParameterizedType) type, toClass, subtypeVarAssigns);
}
if (type instanceof GenericArrayType) {
return getTypeArguments(((GenericArrayType) type).getGenericComponentType(), toClass
.isArray() ? toClass.getComponentType() : toClass, subtypeVarAssigns);
}
// since wildcard types are not assignable to classes, should this just
// return null?
if (type instanceof WildcardType) {
for (Type bound : getImplicitUpperBounds((WildcardType) type)) {
// find the first bound that is assignable to the target class
if (isAssignable(bound, toClass)) {
return getTypeArguments(bound, toClass, subtypeVarAssigns);
}
}
return null;
}
// *
if (type instanceof TypeVariable<?>) {
for (Type bound : getImplicitBounds((TypeVariable<?>) type)) {
// find the first bound that is assignable to the target class
if (isAssignable(bound, toClass)) {
return getTypeArguments(bound, toClass, subtypeVarAssigns);
}
}
return null;
}
// */
throw new IllegalStateException("found an unhandled type: " + type);
}
/**
* <p> Return a map of the type arguments of a parameterized type in the context of <code>toClass</code>. </p>
*
* @param parameterizedType the parameterized type
* @param toClass the class
* @param subtypeVarAssigns a map with type variables
* @return the map with type arguments
*/
private static Map<TypeVariable<?>, Type> getTypeArguments(
ParameterizedType parameterizedType, Class<?> toClass,
Map<TypeVariable<?>, Type> subtypeVarAssigns) {
Class<?> cls = getRawType(parameterizedType);
// make sure they're assignable
if (!isAssignable(cls, toClass)) {
return null;
}
Type ownerType = parameterizedType.getOwnerType();
Map<TypeVariable<?>, Type> typeVarAssigns;
if (ownerType instanceof ParameterizedType) {
// get the owner type arguments first
ParameterizedType parameterizedOwnerType = (ParameterizedType) ownerType;
typeVarAssigns = getTypeArguments(parameterizedOwnerType,
getRawType(parameterizedOwnerType), subtypeVarAssigns);
} else {
// no owner, prep the type variable assignments map
typeVarAssigns = subtypeVarAssigns == null ? new HashMap<TypeVariable<?>, Type>()
: new HashMap<TypeVariable<?>, Type>(subtypeVarAssigns);
}
// get the subject parameterized type's arguments
Type[] typeArgs = parameterizedType.getActualTypeArguments();
// and get the corresponding type variables from the raw class
TypeVariable<?>[] typeParams = cls.getTypeParameters();
// map the arguments to their respective type variables
for (int i = 0; i < typeParams.length; i++) {
Type typeArg = typeArgs[i];
typeVarAssigns.put(typeParams[i], typeVarAssigns.containsKey(typeArg) ? typeVarAssigns
.get(typeArg) : typeArg);
}
if (toClass.equals(cls)) {
// target class has been reached. Done.
return typeVarAssigns;
}
// walk the inheritance hierarchy until the target class is reached
return getTypeArguments(getClosestParentType(cls, toClass), toClass, typeVarAssigns);
}
/**
* <p> Return a map of the type arguments of a class in the context of <code>toClass</code>. </p>
*
* @param cls the class in question
* @param toClass the context class
* @param subtypeVarAssigns a map with type variables
* @return the map with type arguments
*/
private static Map<TypeVariable<?>, Type> getTypeArguments(Class<?> cls, Class<?> toClass,
Map<TypeVariable<?>, Type> subtypeVarAssigns) {
// make sure they're assignable
if (!isAssignable(cls, toClass)) {
return null;
}
// can't work with primitives
if (cls.isPrimitive()) {
// both classes are primitives?
if (toClass.isPrimitive()) {
// dealing with widening here. No type arguments to be
// harvested with these two types.
return new HashMap<TypeVariable<?>, Type>();
}
// work with wrapper the wrapper class instead of the primitive
cls = ClassUtils.primitiveToWrapper(cls);
}
// create a copy of the incoming map, or an empty one if it's null
HashMap<TypeVariable<?>, Type> typeVarAssigns = subtypeVarAssigns == null ? new HashMap<TypeVariable<?>, Type>()
: new HashMap<TypeVariable<?>, Type>(subtypeVarAssigns);
// no arguments for the parameters, or target class has been reached
if (cls.getTypeParameters().length > 0 || toClass.equals(cls)) {
return typeVarAssigns;
}
// walk the inheritance hierarchy until the target class is reached
return getTypeArguments(getClosestParentType(cls, toClass), toClass, typeVarAssigns);
}
/**
* <p> Tries to determine the type arguments of a class/interface based on a
* super parameterized type's type arguments. This method is the inverse of
* {@link #getTypeArguments(Type, Class)} which gets a class/interface's
* type arguments based on a subtype. It is far more limited in determining
* the type arguments for the subject class's type variables in that it can
* only determine those parameters that map from the subject {@link Class}
* object to the supertype. </p> <p> Example: {@link java.util.TreeSet
* TreeSet} sets its parameter as the parameter for
* {@link java.util.NavigableSet NavigableSet}, which in turn sets the
* parameter of {@link java.util.SortedSet}, which in turn sets the
* parameter of {@link Set}, which in turn sets the parameter of
* {@link java.util.Collection}, which in turn sets the parameter of
* {@link java.lang.Iterable}. Since <code>TreeSet</code>'s parameter maps
* (indirectly) to <code>Iterable</code>'s parameter, it will be able to
* determine that based on the super type <code>Iterable<? extends
* Map<Integer,? extends Collection<?>>></code>, the parameter of
* <code>TreeSet</code> is <code>? extends Map<Integer,? extends
* Collection<?>></code>. </p>
*
* @param cls the class whose type parameters are to be determined
* @param superType the super type from which <code>cls</code>'s type
* arguments are to be determined
* @return a map of the type assignments that could be determined for the
* type variables in each type in the inheritance hierarchy from
* <code>type</code> to <code>toClass</code> inclusive.
*/
public static Map<TypeVariable<?>, Type> determineTypeArguments(Class<?> cls,
ParameterizedType superType) {
Class<?> superClass = getRawType(superType);
// compatibility check
if (!isAssignable(cls, superClass)) {
return null;
}
if (cls.equals(superClass)) {
return getTypeArguments(superType, superClass, null);
}
// get the next class in the inheritance hierarchy
Type midType = getClosestParentType(cls, superClass);
// can only be a class or a parameterized type
if (midType instanceof Class<?>) {
return determineTypeArguments((Class<?>) midType, superType);
}
ParameterizedType midParameterizedType = (ParameterizedType) midType;
Class<?> midClass = getRawType(midParameterizedType);
// get the type variables of the mid class that map to the type
// arguments of the super class
Map<TypeVariable<?>, Type> typeVarAssigns = determineTypeArguments(midClass, superType);
// map the arguments of the mid type to the class type variables
mapTypeVariablesToArguments(cls, midParameterizedType, typeVarAssigns);
return typeVarAssigns;
}
/**
* <p>Performs a mapping of type variables.</p>
*
* @param <T> the generic type of the class in question
* @param cls the class in question
* @param parameterizedType the parameterized type
* @param typeVarAssigns the map to be filled
*/
private static <T> void mapTypeVariablesToArguments(Class<T> cls,
ParameterizedType parameterizedType, Map<TypeVariable<?>, Type> typeVarAssigns) {
// capture the type variables from the owner type that have assignments
Type ownerType = parameterizedType.getOwnerType();
if (ownerType instanceof ParameterizedType) {
// recursion to make sure the owner's owner type gets processed
mapTypeVariablesToArguments(cls, (ParameterizedType) ownerType, typeVarAssigns);
}
// parameterizedType is a generic interface/class (or it's in the owner
// hierarchy of said interface/class) implemented/extended by the class
// cls. Find out which type variables of cls are type arguments of
// parameterizedType:
Type[] typeArgs = parameterizedType.getActualTypeArguments();
// of the cls's type variables that are arguments of parameterizedType,
// find out which ones can be determined from the super type's arguments
TypeVariable<?>[] typeVars = getRawType(parameterizedType).getTypeParameters();
// use List view of type parameters of cls so the contains() method can be used:
List<TypeVariable<Class<T>>> typeVarList = Arrays.asList(cls
.getTypeParameters());
for (int i = 0; i < typeArgs.length; i++) {
TypeVariable<?> typeVar = typeVars[i];
Type typeArg = typeArgs[i];
// argument of parameterizedType is a type variable of cls
if (typeVarList.contains(typeArg)
// type variable of parameterizedType has an assignment in
// the super type.
&& typeVarAssigns.containsKey(typeVar)) {
// map the assignment to the cls's type variable
typeVarAssigns.put((TypeVariable<?>) typeArg, typeVarAssigns.get(typeVar));
}
}
}
/**
* <p> Closest parent type? Closest to what? The closest parent type to the
* super class specified by <code>superClass</code>. </p>
*
* @param cls the class in question
* @param superClass the super class
* @return the closes parent type
*/
private static Type getClosestParentType(Class<?> cls, Class<?> superClass) {
// only look at the interfaces if the super class is also an interface
if (superClass.isInterface()) {
// get the generic interfaces of the subject class
Type[] interfaceTypes = cls.getGenericInterfaces();
// will hold the best generic interface match found
Type genericInterface = null;
// find the interface closest to the super class
for (Type midType : interfaceTypes) {
Class<?> midClass = null;
if (midType instanceof ParameterizedType) {
midClass = getRawType((ParameterizedType) midType);
} else if (midType instanceof Class<?>) {
midClass = (Class<?>) midType;
} else {
throw new IllegalStateException("Unexpected generic"
+ " interface type found: " + midType);
}
// check if this interface is further up the inheritance chain
// than the previously found match
if (isAssignable(midClass, superClass)
&& isAssignable(genericInterface, (Type) midClass)) {
genericInterface = midType;
}
}
// found a match?
if (genericInterface != null) {
return genericInterface;
}
}
// none of the interfaces were descendants of the target class, so the
// super class has to be one, instead
return cls.getGenericSuperclass();
}
/**
* <p> Checks if the given value can be assigned to the target type
* following the Java generics rules. </p>
*
* @param value the value to be checked
* @param type the target type
* @return true of <code>value</code> is an instance of <code>type</code>.
*/
public static boolean isInstance(Object value, Type type) {
if (type == null) {
return false;
}
return value == null ? !(type instanceof Class<?>) || !((Class<?>) type).isPrimitive()
: isAssignable(value.getClass(), type, null);
}
/**
* <p> This method strips out the redundant upper bound types in type
* variable types and wildcard types (or it would with wildcard types if
* multiple upper bounds were allowed). </p> <p> Example: with the variable
* type declaration:
*
* <pre> <K extends java.util.Collection<String> &
* java.util.List<String>> </pre>
*
* since <code>List</code> is a subinterface of <code>Collection</code>,
* this method will return the bounds as if the declaration had been:
*
* <pre> <K extends java.util.List<String>> </pre>
*
* </p>
*
* @param bounds an array of types representing the upper bounds of either
* <code>WildcardType</code> or <code>TypeVariable</code>.
* @return an array containing the values from <code>bounds</code> minus the
* redundant types.
*/
public static Type[] normalizeUpperBounds(Type[] bounds) {
// don't bother if there's only one (or none) type
if (bounds.length < 2) {
return bounds;
}
Set<Type> types = new HashSet<Type>(bounds.length);
for (Type type1 : bounds) {
boolean subtypeFound = false;
for (Type type2 : bounds) {
if (type1 != type2 && isAssignable(type2, type1, null)) {
subtypeFound = true;
break;
}
}
if (!subtypeFound) {
types.add(type1);
}
}
return types.toArray(new Type[types.size()]);
}
/**
* <p> Returns an array containing the sole type of {@link Object} if
* {@link TypeVariable#getBounds()} returns an empty array. Otherwise, it
* returns the result of <code>TypeVariable.getBounds()</code> passed into
* {@link #normalizeUpperBounds}. </p>
*
* @param typeVariable the subject type variable
* @return a non-empty array containing the bounds of the type variable.
*/
public static Type[] getImplicitBounds(TypeVariable<?> typeVariable) {
Type[] bounds = typeVariable.getBounds();
return bounds.length == 0 ? new Type[] { Object.class } : normalizeUpperBounds(bounds);
}
/**
* <p> Returns an array containing the sole value of {@link Object} if
* {@link WildcardType#getUpperBounds()} returns an empty array. Otherwise,
* it returns the result of <code>WildcardType.getUpperBounds()</code>
* passed into {@link #normalizeUpperBounds}. </p>
*
* @param wildcardType the subject wildcard type
* @return a non-empty array containing the upper bounds of the wildcard
* type.
*/
public static Type[] getImplicitUpperBounds(WildcardType wildcardType) {
Type[] bounds = wildcardType.getUpperBounds();
return bounds.length == 0 ? new Type[] { Object.class } : normalizeUpperBounds(bounds);
}
/**
* <p> Returns an array containing a single value of <code>null</code> if
* {@link WildcardType#getLowerBounds()} returns an empty array. Otherwise,
* it returns the result of <code>WildcardType.getLowerBounds()</code>. </p>
*
* @param wildcardType the subject wildcard type
* @return a non-empty array containing the lower bounds of the wildcard
* type.
*/
public static Type[] getImplicitLowerBounds(WildcardType wildcardType) {
Type[] bounds = wildcardType.getLowerBounds();
return bounds.length == 0 ? new Type[] { null } : bounds;
}
/**
* <p> Determines whether or not specified types satisfy the bounds of their
* mapped type variables. When a type parameter extends another (such as
* <code><T, S extends T></code>), uses another as a type parameter (such as
* <code><T, S extends Comparable<T></code>), or otherwise depends on
* another type variable to be specified, the dependencies must be included
* in <code>typeVarAssigns</code>. </p>
*
* @param typeVarAssigns specifies the potential types to be assigned to the
* type variables.
* @return whether or not the types can be assigned to their respective type
* variables.
*/
public static boolean typesSatisfyVariables(Map<TypeVariable<?>, Type> typeVarAssigns) {
// all types must be assignable to all the bounds of the their mapped
// type variable.
for (Map.Entry<TypeVariable<?>, Type> entry : typeVarAssigns.entrySet()) {
TypeVariable<?> typeVar = entry.getKey();
Type type = entry.getValue();
for (Type bound : getImplicitBounds(typeVar)) {
if (!isAssignable(type, substituteTypeVariables(bound, typeVarAssigns),
typeVarAssigns)) {
return false;
}
}
}
return true;
}
/**
* <p> Transforms the passed in type to a {@code Class} object. Type-checking method of convenience. </p>
*
* @param parameterizedType the type to be converted
* @return the corresponding {@code Class} object
* @throws IllegalStateException if the conversion fails
*/
private static Class<?> getRawType(ParameterizedType parameterizedType) {
Type rawType = parameterizedType.getRawType();
// check if raw type is a Class object
// not currently necessary, but since the return type is Type instead of
// Class, there's enough reason to believe that future versions of Java
// may return other Type implementations. And type-safety checking is
// rarely a bad idea.
if (!(rawType instanceof Class<?>)) {
throw new IllegalStateException("Wait... What!? Type of rawType: " + rawType);
}
return (Class<?>) rawType;
}
/**
* <p> Get the raw type of a Java type, given its context. Primarily for use
* with {@link TypeVariable}s and {@link GenericArrayType}s, or when you do
* not know the runtime type of <code>type</code>: if you know you have a
* {@link Class} instance, it is already raw; if you know you have a
* {@link ParameterizedType}, its raw type is only a method call away. </p>
*
* @param type to resolve
* @param assigningType type to be resolved against
* @return the resolved <code>Class</code> object or <code>null</code> if
* the type could not be resolved
*/
public static Class<?> getRawType(Type type, Type assigningType) {
if (type instanceof Class<?>) {
// it is raw, no problem
return (Class<?>) type;
}
if (type instanceof ParameterizedType) {
// simple enough to get the raw type of a ParameterizedType
return getRawType((ParameterizedType) type);
}
if (type instanceof TypeVariable<?>) {
if (assigningType == null) {
return null;
}
// get the entity declaring this type variable
Object genericDeclaration = ((TypeVariable<?>) type).getGenericDeclaration();
// can't get the raw type of a method- or constructor-declared type
// variable
if (!(genericDeclaration instanceof Class<?>)) {
return null;
}
// get the type arguments for the declaring class/interface based
// on the enclosing type
Map<TypeVariable<?>, Type> typeVarAssigns = getTypeArguments(assigningType,
(Class<?>) genericDeclaration);
// enclosingType has to be a subclass (or subinterface) of the
// declaring type
if (typeVarAssigns == null) {
return null;
}
// get the argument assigned to this type variable
Type typeArgument = typeVarAssigns.get(type);
if (typeArgument == null) {
return null;
}
// get the argument for this type variable
return getRawType(typeArgument, assigningType);
}
if (type instanceof GenericArrayType) {
// get raw component type
Class<?> rawComponentType = getRawType(((GenericArrayType) type)
.getGenericComponentType(), assigningType);
// create array type from raw component type and return its class
return Array.newInstance(rawComponentType, 0).getClass();
}
// (hand-waving) this is not the method you're looking for
if (type instanceof WildcardType) {
return null;
}
throw new IllegalArgumentException("unknown type: " + type);
}
/**
* Learn whether the specified type denotes an array type.
* @param type the type to be checked
* @return <code>true</code> if <code>type</code> is an array class or a {@link GenericArrayType}.
*/
public static boolean isArrayType(Type type) {
return type instanceof GenericArrayType || type instanceof Class<?> && ((Class<?>) type).isArray();
}
/**
* Get the array component type of <code>type</code>.
* @param type the type to be checked
* @return component type or null if type is not an array type
*/
public static Type getArrayComponentType(Type type) {
if (type instanceof Class<?>) {
Class<?> clazz = (Class<?>) type;
return clazz.isArray() ? clazz.getComponentType() : null;
}
if (type instanceof GenericArrayType) {
return ((GenericArrayType) type).getGenericComponentType();
}
return null;
}
}