453 lines
16 KiB
Java
453 lines
16 KiB
Java
/*
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* Copyright (C) 2008 Google Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.google.gson.reflect;
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import com.google.gson.internal.$Gson$Types;
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import com.google.gson.internal.TroubleshootingGuide;
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import java.lang.reflect.GenericArrayType;
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import java.lang.reflect.ParameterizedType;
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import java.lang.reflect.Type;
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import java.lang.reflect.TypeVariable;
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import java.lang.reflect.WildcardType;
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import java.util.HashMap;
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import java.util.Map;
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import java.util.Objects;
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/**
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* Represents a generic type {@code T}. Java doesn't yet provide a way to represent generic types,
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* so this class does. Forces clients to create a subclass of this class which enables retrieval the
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* type information even at runtime.
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*
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* <p>For example, to create a type literal for {@code List<String>}, you can create an empty
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* anonymous class:
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*
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* <p>{@code TypeToken<List<String>> list = new TypeToken<List<String>>() {};}
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*
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* <p>Capturing a type variable as type argument of an anonymous {@code TypeToken} subclass is not
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* allowed, for example {@code TypeToken<List<T>>}. Due to type erasure the runtime type of a type
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* variable is not available to Gson and therefore it cannot provide the functionality one might
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* expect. This would give a false sense of type-safety at compile time and could lead to an
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* unexpected {@code ClassCastException} at runtime.
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*
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* <p>If the type arguments of the parameterized type are only available at runtime, for example
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* when you want to create a {@code List<E>} based on a {@code Class<E>} representing the element
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* type, the method {@link #getParameterized(Type, Type...)} can be used.
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*
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* @author Bob Lee
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* @author Sven Mawson
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* @author Jesse Wilson
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*/
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public class TypeToken<T> {
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private final Class<? super T> rawType;
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private final Type type;
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private final int hashCode;
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/**
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* Constructs a new type literal. Derives represented class from type parameter.
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*
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* <p>Clients create an empty anonymous subclass. Doing so embeds the type parameter in the
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* anonymous class's type hierarchy so we can reconstitute it at runtime despite erasure, for
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* example:
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*
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* <p>{@code new TypeToken<List<String>>() {}}
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*
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* @throws IllegalArgumentException If the anonymous {@code TypeToken} subclass captures a type
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* variable, for example {@code TypeToken<List<T>>}. See the {@code TypeToken} class
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* documentation for more details.
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*/
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@SuppressWarnings("unchecked")
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protected TypeToken() {
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this.type = getTypeTokenTypeArgument();
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this.rawType = (Class<? super T>) $Gson$Types.getRawType(type);
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this.hashCode = type.hashCode();
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}
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/** Unsafe. Constructs a type literal manually. */
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@SuppressWarnings("unchecked")
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private TypeToken(Type type) {
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this.type = $Gson$Types.canonicalize(Objects.requireNonNull(type));
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this.rawType = (Class<? super T>) $Gson$Types.getRawType(this.type);
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this.hashCode = this.type.hashCode();
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}
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private static boolean isCapturingTypeVariablesForbidden() {
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return !Objects.equals(System.getProperty("gson.allowCapturingTypeVariables"), "true");
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}
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/**
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* Verifies that {@code this} is an instance of a direct subclass of TypeToken and returns the
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* type argument for {@code T} in {@link $Gson$Types#canonicalize canonical form}.
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*/
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private Type getTypeTokenTypeArgument() {
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Type superclass = getClass().getGenericSuperclass();
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if (superclass instanceof ParameterizedType) {
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ParameterizedType parameterized = (ParameterizedType) superclass;
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if (parameterized.getRawType() == TypeToken.class) {
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Type typeArgument = $Gson$Types.canonicalize(parameterized.getActualTypeArguments()[0]);
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if (isCapturingTypeVariablesForbidden()) {
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verifyNoTypeVariable(typeArgument);
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}
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return typeArgument;
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}
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}
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// Check for raw TypeToken as superclass
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else if (superclass == TypeToken.class) {
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throw new IllegalStateException(
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"TypeToken must be created with a type argument: new TypeToken<...>() {}; When using code"
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+ " shrinkers (ProGuard, R8, ...) make sure that generic signatures are preserved."
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+ "\nSee "
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+ TroubleshootingGuide.createUrl("type-token-raw"));
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}
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// User created subclass of subclass of TypeToken
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throw new IllegalStateException("Must only create direct subclasses of TypeToken");
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}
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private static void verifyNoTypeVariable(Type type) {
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if (type instanceof TypeVariable) {
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TypeVariable<?> typeVariable = (TypeVariable<?>) type;
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throw new IllegalArgumentException(
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"TypeToken type argument must not contain a type variable; captured type variable "
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+ typeVariable.getName()
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+ " declared by "
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+ typeVariable.getGenericDeclaration()
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+ "\nSee "
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+ TroubleshootingGuide.createUrl("typetoken-type-variable"));
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} else if (type instanceof GenericArrayType) {
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verifyNoTypeVariable(((GenericArrayType) type).getGenericComponentType());
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} else if (type instanceof ParameterizedType) {
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ParameterizedType parameterizedType = (ParameterizedType) type;
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Type ownerType = parameterizedType.getOwnerType();
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if (ownerType != null) {
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verifyNoTypeVariable(ownerType);
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}
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for (Type typeArgument : parameterizedType.getActualTypeArguments()) {
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verifyNoTypeVariable(typeArgument);
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}
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} else if (type instanceof WildcardType) {
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WildcardType wildcardType = (WildcardType) type;
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for (Type bound : wildcardType.getLowerBounds()) {
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verifyNoTypeVariable(bound);
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}
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for (Type bound : wildcardType.getUpperBounds()) {
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verifyNoTypeVariable(bound);
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}
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} else if (type == null) {
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// Occurs in Eclipse IDE and certain Java versions (e.g. Java 11.0.18) when capturing type
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// variable declared by method of local class, see
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// https://github.com/eclipse-jdt/eclipse.jdt.core/issues/975
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throw new IllegalArgumentException(
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"TypeToken captured `null` as type argument; probably a compiler / runtime bug");
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}
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}
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/** Returns the raw (non-generic) type for this type. */
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public final Class<? super T> getRawType() {
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return rawType;
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}
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/** Gets underlying {@code Type} instance. */
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public final Type getType() {
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return type;
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}
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/**
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* Check if this type is assignable from the given class object.
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*
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* @deprecated this implementation may be inconsistent with javac for types with wildcards.
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*/
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@Deprecated
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public boolean isAssignableFrom(Class<?> cls) {
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return isAssignableFrom((Type) cls);
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}
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/**
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* Check if this type is assignable from the given Type.
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*
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* @deprecated this implementation may be inconsistent with javac for types with wildcards.
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*/
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@Deprecated
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public boolean isAssignableFrom(Type from) {
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if (from == null) {
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return false;
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}
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if (type.equals(from)) {
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return true;
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}
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if (type instanceof Class<?>) {
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return rawType.isAssignableFrom($Gson$Types.getRawType(from));
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} else if (type instanceof ParameterizedType) {
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return isAssignableFrom(from, (ParameterizedType) type, new HashMap<String, Type>());
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} else if (type instanceof GenericArrayType) {
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return rawType.isAssignableFrom($Gson$Types.getRawType(from))
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&& isAssignableFrom(from, (GenericArrayType) type);
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} else {
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throw buildUnsupportedTypeException(
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type, Class.class, ParameterizedType.class, GenericArrayType.class);
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}
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}
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/**
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* Check if this type is assignable from the given type token.
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*
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* @deprecated this implementation may be inconsistent with javac for types with wildcards.
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*/
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@Deprecated
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public boolean isAssignableFrom(TypeToken<?> token) {
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return isAssignableFrom(token.getType());
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}
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/**
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* Private helper function that performs some assignability checks for the provided
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* GenericArrayType.
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*/
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private static boolean isAssignableFrom(Type from, GenericArrayType to) {
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Type toGenericComponentType = to.getGenericComponentType();
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if (toGenericComponentType instanceof ParameterizedType) {
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Type t = from;
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if (from instanceof GenericArrayType) {
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t = ((GenericArrayType) from).getGenericComponentType();
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} else if (from instanceof Class<?>) {
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Class<?> classType = (Class<?>) from;
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while (classType.isArray()) {
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classType = classType.getComponentType();
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}
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t = classType;
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}
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return isAssignableFrom(
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t, (ParameterizedType) toGenericComponentType, new HashMap<String, Type>());
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}
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// No generic defined on "to"; therefore, return true and let other
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// checks determine assignability
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return true;
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}
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/** Private recursive helper function to actually do the type-safe checking of assignability. */
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private static boolean isAssignableFrom(
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Type from, ParameterizedType to, Map<String, Type> typeVarMap) {
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if (from == null) {
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return false;
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}
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if (to.equals(from)) {
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return true;
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}
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// First figure out the class and any type information.
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Class<?> clazz = $Gson$Types.getRawType(from);
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ParameterizedType ptype = null;
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if (from instanceof ParameterizedType) {
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ptype = (ParameterizedType) from;
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}
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// Load up parameterized variable info if it was parameterized.
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if (ptype != null) {
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Type[] tArgs = ptype.getActualTypeArguments();
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TypeVariable<?>[] tParams = clazz.getTypeParameters();
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for (int i = 0; i < tArgs.length; i++) {
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Type arg = tArgs[i];
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TypeVariable<?> var = tParams[i];
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while (arg instanceof TypeVariable<?>) {
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TypeVariable<?> v = (TypeVariable<?>) arg;
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arg = typeVarMap.get(v.getName());
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}
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typeVarMap.put(var.getName(), arg);
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}
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// check if they are equivalent under our current mapping.
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if (typeEquals(ptype, to, typeVarMap)) {
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return true;
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}
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}
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for (Type itype : clazz.getGenericInterfaces()) {
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if (isAssignableFrom(itype, to, new HashMap<>(typeVarMap))) {
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return true;
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}
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}
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// Interfaces didn't work, try the superclass.
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Type sType = clazz.getGenericSuperclass();
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return isAssignableFrom(sType, to, new HashMap<>(typeVarMap));
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}
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/**
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* Checks if two parameterized types are exactly equal, under the variable replacement described
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* in the typeVarMap.
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*/
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private static boolean typeEquals(
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ParameterizedType from, ParameterizedType to, Map<String, Type> typeVarMap) {
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if (from.getRawType().equals(to.getRawType())) {
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Type[] fromArgs = from.getActualTypeArguments();
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Type[] toArgs = to.getActualTypeArguments();
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for (int i = 0; i < fromArgs.length; i++) {
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if (!matches(fromArgs[i], toArgs[i], typeVarMap)) {
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return false;
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}
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}
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return true;
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}
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return false;
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}
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private static IllegalArgumentException buildUnsupportedTypeException(
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Type token, Class<?>... expected) {
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// Build exception message
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StringBuilder exceptionMessage = new StringBuilder("Unsupported type, expected one of: ");
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for (Class<?> clazz : expected) {
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exceptionMessage.append(clazz.getName()).append(", ");
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}
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exceptionMessage
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.append("but got: ")
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.append(token.getClass().getName())
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.append(", for type token: ")
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.append(token.toString());
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return new IllegalArgumentException(exceptionMessage.toString());
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}
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/**
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* Checks if two types are the same or are equivalent under a variable mapping given in the type
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* map that was provided.
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*/
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private static boolean matches(Type from, Type to, Map<String, Type> typeMap) {
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return to.equals(from)
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|| (from instanceof TypeVariable
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&& to.equals(typeMap.get(((TypeVariable<?>) from).getName())));
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}
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@Override
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public final int hashCode() {
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return this.hashCode;
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}
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@Override
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public final boolean equals(Object o) {
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return o instanceof TypeToken<?> && $Gson$Types.equals(type, ((TypeToken<?>) o).type);
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}
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@Override
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public final String toString() {
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return $Gson$Types.typeToString(type);
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}
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/** Gets type literal for the given {@code Type} instance. */
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public static TypeToken<?> get(Type type) {
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return new TypeToken<>(type);
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}
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/** Gets type literal for the given {@code Class} instance. */
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public static <T> TypeToken<T> get(Class<T> type) {
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return new TypeToken<>(type);
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}
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/**
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* Gets a type literal for the parameterized type represented by applying {@code typeArguments} to
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* {@code rawType}. This is mainly intended for situations where the type arguments are not
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* available at compile time. The following example shows how a type token for {@code Map<K, V>}
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* can be created:
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*
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* <pre>{@code
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* Class<K> keyClass = ...;
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* Class<V> valueClass = ...;
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* TypeToken<?> mapTypeToken = TypeToken.getParameterized(Map.class, keyClass, valueClass);
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* }</pre>
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*
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* As seen here the result is a {@code TypeToken<?>}; this method cannot provide any type-safety,
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* and care must be taken to pass in the correct number of type arguments.
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*
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* <p>If {@code rawType} is a non-generic class and no type arguments are provided, this method
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* simply delegates to {@link #get(Class)} and creates a {@code TypeToken(Class)}.
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*
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* @throws IllegalArgumentException If {@code rawType} is not of type {@code Class}, or if the
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* type arguments are invalid for the raw type
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*/
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public static TypeToken<?> getParameterized(Type rawType, Type... typeArguments) {
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Objects.requireNonNull(rawType);
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Objects.requireNonNull(typeArguments);
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// Perform basic validation here because this is the only public API where users
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// can create malformed parameterized types
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if (!(rawType instanceof Class)) {
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// See also https://bugs.openjdk.org/browse/JDK-8250659
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throw new IllegalArgumentException("rawType must be of type Class, but was " + rawType);
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}
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Class<?> rawClass = (Class<?>) rawType;
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TypeVariable<?>[] typeVariables = rawClass.getTypeParameters();
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int expectedArgsCount = typeVariables.length;
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int actualArgsCount = typeArguments.length;
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if (actualArgsCount != expectedArgsCount) {
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throw new IllegalArgumentException(
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rawClass.getName()
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+ " requires "
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+ expectedArgsCount
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+ " type arguments, but got "
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+ actualArgsCount);
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}
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// For legacy reasons create a TypeToken(Class) if the type is not generic
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if (typeArguments.length == 0) {
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return get(rawClass);
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}
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// Check for this here to avoid misleading exception thrown by ParameterizedTypeImpl
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if ($Gson$Types.requiresOwnerType(rawType)) {
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throw new IllegalArgumentException(
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"Raw type "
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+ rawClass.getName()
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+ " is not supported because it requires specifying an owner type");
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}
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for (int i = 0; i < expectedArgsCount; i++) {
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Type typeArgument =
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Objects.requireNonNull(typeArguments[i], "Type argument must not be null");
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Class<?> rawTypeArgument = $Gson$Types.getRawType(typeArgument);
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TypeVariable<?> typeVariable = typeVariables[i];
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for (Type bound : typeVariable.getBounds()) {
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Class<?> rawBound = $Gson$Types.getRawType(bound);
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if (!rawBound.isAssignableFrom(rawTypeArgument)) {
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throw new IllegalArgumentException(
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"Type argument "
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+ typeArgument
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+ " does not satisfy bounds for type variable "
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+ typeVariable
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+ " declared by "
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+ rawType);
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}
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}
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}
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return new TypeToken<>($Gson$Types.newParameterizedTypeWithOwner(null, rawType, typeArguments));
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}
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/**
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* Gets type literal for the array type whose elements are all instances of {@code componentType}.
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*/
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public static TypeToken<?> getArray(Type componentType) {
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return new TypeToken<>($Gson$Types.arrayOf(componentType));
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}
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}
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