/*
* Copyright (C) 2008 Google Inc.
*
* 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 com.google.gson.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.util.HashMap;
import java.util.Map;
/**
* Represents a generic type {@code T}.
*
* You can use this class to get the generic type for a class. For example,
* to get the generic type for <code>Collection<Foo></code>, you can use:
* <p>
* <code>Type typeOfCollectionOfFoo = new TypeToken<Collection<Foo>>(){}.getType()
* </code>
*
* <p>Assumes {@code Type} implements {@code equals()} and {@code hashCode()}
* as a value (as opposed to identity) comparison.
*
* Also implements {@link #isAssignableFrom(Type)} to check type-safe
* assignability.
*
* @author Bob Lee
* @author Sven Mawson
*/
public abstract class TypeToken<T> {
final Class<? super T> rawType;
final Type type;
/**
* Constructs a new type token. Derives represented class from type
* parameter.
*
* <p>Clients create an empty anonymous subclass. Doing so embeds the type
* parameter in the anonymous class's type hierarchy so we can reconstitute
* it at runtime despite erasure.
*
* <p>For example:
* <code>
* {@literal TypeToken<List<String>> t = new TypeToken<List<String>>}(){}
* </code>
*/
@SuppressWarnings("unchecked")
protected TypeToken() {
this.type = getSuperclassTypeParameter(getClass());
this.rawType = (Class<? super T>) getRawType(type);
}
/**
* Unsafe. Constructs a type token manually.
*/
@SuppressWarnings({"unchecked"})
private TypeToken(Type type) {
this.rawType = (Class<? super T>) getRawType(nonNull(type, "type"));
this.type = type;
}
private static <T> T nonNull(T o, String message) {
if (o == null) {
throw new NullPointerException(message);
}
return o;
}
/**
* Gets type from super class's type parameter.
*/
static Type getSuperclassTypeParameter(Class<?> subclass) {
Type superclass = subclass.getGenericSuperclass();
if (superclass instanceof Class<?>) {
throw new RuntimeException("Missing type parameter.");
}
return ((ParameterizedType) superclass).getActualTypeArguments()[0];
}
/**
* Gets type token from super class's type parameter.
*/
static TypeToken<?> fromSuperclassTypeParameter(Class<?> subclass) {
return new SimpleTypeToken<Object>(subclass);
}
private static Class<?> getRawType(Type type) {
if (type instanceof Class<?>) {
// type is a normal class.
return (Class<?>) type;
} else if (type instanceof ParameterizedType) {
ParameterizedType parameterizedType = (ParameterizedType) type;
// I'm not exactly sure why getRawType() returns Type instead of Class.
// Neal isn't either but suspects some pathological case related
// to nested classes exists.
Type rawType = parameterizedType.getRawType();
if (rawType instanceof Class<?>) {
return (Class<?>) rawType;
}
throw buildUnexpectedTypeError(rawType, Class.class);
} else if (type instanceof GenericArrayType) {
GenericArrayType genericArrayType = (GenericArrayType) type;
// TODO(jleitch): This is not the most efficient way to handle generic
// arrays, but is there another way to extract the array class in a
// non-hacky way (i.e. using String value class names- "[L...")?
Object rawArrayType = Array.newInstance(
getRawType(genericArrayType.getGenericComponentType()), 0);
return rawArrayType.getClass();
} else {
throw buildUnexpectedTypeError(
type, ParameterizedType.class, GenericArrayType.class);
}
}
/**
* Gets the raw type.
*/
public Class<? super T> getRawType() {
return rawType;
}
/**
* Gets underlying {@code Type} instance.
*/
public Type getType() {
return type;
}
/**
* Check if this type is assignable from the given class object.
*/
public boolean isAssignableFrom(Class<?> cls) {
return isAssignableFrom((Type) cls);
}
/**
* Check if this type is assignable from the given Type.
*/
public boolean isAssignableFrom(Type from) {
if (from == null) {
return false;
}
if (type.equals(from)) {
return true;
}
if (type instanceof Class<?>) {
return rawType.isAssignableFrom(getRawType(from));
} else if (type instanceof ParameterizedType) {
return isAssignableFrom(from, (ParameterizedType) type,
new HashMap<String, Type>());
} else if (type instanceof GenericArrayType) {
return rawType.isAssignableFrom(getRawType(from))
&& isAssignableFrom(from, (GenericArrayType) type);
} else {
throw buildUnexpectedTypeError(
type, Class.class, ParameterizedType.class, GenericArrayType.class);
}
}
/**
* Check if this type is assignable from the given type token.
*/
public boolean isAssignableFrom(TypeToken<?> token) {
return isAssignableFrom(token.getType());
}
/**
* Private helper function that performs some assignability checks for
* the provided GenericArrayType.
*/
private static boolean isAssignableFrom(Type from, GenericArrayType to) {
Type toGenericComponentType = to.getGenericComponentType();
if (toGenericComponentType instanceof ParameterizedType) {
Type t = from;
if (from instanceof GenericArrayType) {
t = ((GenericArrayType) from).getGenericComponentType();
} else if (from instanceof Class<?>) {
Class<?> classType = (Class<?>) from;
while (classType.isArray()) {
classType = classType.getComponentType();
}
t = classType;
}
return isAssignableFrom(t, (ParameterizedType) toGenericComponentType,
new HashMap<String, Type>());
}
// No generic defined on "to"; therefore, return true and let other
// checks determine assignability
return true;
}
/**
* Private recursive helper function to actually do the type-safe checking
* of assignability.
*/
private static boolean isAssignableFrom(Type from, ParameterizedType to,
Map<String, Type> typeVarMap) {
if (from == null) {
return false;
}
if (to.equals(from)) {
return true;
}
// First figure out the class and any type information.
Class<?> clazz = getRawType(from);
ParameterizedType ptype = null;
if (from instanceof ParameterizedType) {
ptype = (ParameterizedType) from;
}
// Load up parameterized variable info if it was parameterized.
if (ptype != null) {
Type[] tArgs = ptype.getActualTypeArguments();
TypeVariable<?>[] tParams = clazz.getTypeParameters();
for (int i = 0; i < tArgs.length; i++) {
Type arg = tArgs[i];
TypeVariable<?> var = tParams[i];
while (arg instanceof TypeVariable<?>) {
TypeVariable<?> v = (TypeVariable<?>) arg;
arg = typeVarMap.get(v.getName());
}
typeVarMap.put(var.getName(), arg);
}
// check if they are equivalent under our current mapping.
if (typeEquals(ptype, to, typeVarMap)) {
return true;
}
}
for (Type itype : clazz.getGenericInterfaces()) {
if (isAssignableFrom(itype, to, new HashMap<String, Type>(typeVarMap))) {
return true;
}
}
// Interfaces didn't work, try the superclass.
Type sType = clazz.getGenericSuperclass();
if (isAssignableFrom(sType, to, new HashMap<String, Type>(typeVarMap))) {
return true;
}
return false;
}
/**
* Checks if two parameterized types are exactly equal, under the variable
* replacement described in the typeVarMap.
*/
private static boolean typeEquals(ParameterizedType from,
ParameterizedType to, Map<String, Type> typeVarMap) {
if (from.getRawType().equals(to.getRawType())) {
Type[] fromArgs = from.getActualTypeArguments();
Type[] toArgs = to.getActualTypeArguments();
for (int i = 0; i < fromArgs.length; i++) {
if (!matches(fromArgs[i], toArgs[i], typeVarMap)) {
return false;
}
}
return true;
}
return false;
}
/**
* Checks if two types are the same or are equivalent under a variable mapping
* given in the type map that was provided.
*/
private static boolean matches(Type from, Type to,
Map<String, Type> typeMap) {
if (to.equals(from)) return true;
if (from instanceof TypeVariable<?>) {
return to.equals(typeMap.get(((TypeVariable<?>)from).getName()));
}
return false;
}
/**
* Hashcode for this object.
* @return hashcode for this object.
*/
@Override public int hashCode() {
return type.hashCode();
}
/**
* Method to test equality.
*
* @return true if this object is logically equal to the specified object, false otherwise.
*/
@Override public boolean equals(Object o) {
if (o == this) {
return true;
}
if (!(o instanceof TypeToken<?>)) {
return false;
}
TypeToken<?> t = (TypeToken<?>) o;
return type.equals(t.type);
}
/**
* Returns a string representation of this object.
* @return a string representation of this object.
*/
@Override public String toString() {
return type instanceof Class<?>
? ((Class<?>) type).getName()
: type.toString();
}
private static AssertionError buildUnexpectedTypeError(
Type token, Class<?>... expected) {
// Build exception message
StringBuilder exceptionMessage =
new StringBuilder("Unexpected type. Expected one of: ");
for (Class<?> clazz : expected) {
exceptionMessage.append(clazz.getName()).append(", ");
}
exceptionMessage.append("but got: ").append(token.getClass().getName())
.append(", for type token: ").append(token.toString()).append('.');
return new AssertionError(exceptionMessage.toString());
}
/**
* Gets type token for the given {@code Type} instance.
*/
public static TypeToken<?> get(Type type) {
return new SimpleTypeToken<Object>(type);
}
/**
* Gets type token for the given {@code Class} instance.
*/
public static <T> TypeToken<T> get(Class<T> type) {
return new SimpleTypeToken<T>(type);
}
/**
* Private static class to not create more anonymous classes than
* necessary.
*/
private static class SimpleTypeToken<T> extends TypeToken<T> {
public SimpleTypeToken(Type type) {
super(type);
}
}
}