d8d8ccb98a
When we maintain the label value, we do not need to make a new JsonObject and copy over the keys and values when writing. The ordering will change, though. Before this change, it always put the label first.
266 lines
9.7 KiB
Java
266 lines
9.7 KiB
Java
/*
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* Copyright (C) 2011 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.typeadapters;
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import java.io.IOException;
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import java.util.LinkedHashMap;
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import java.util.Map;
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import com.google.gson.Gson;
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import com.google.gson.JsonElement;
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import com.google.gson.JsonObject;
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import com.google.gson.JsonParseException;
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import com.google.gson.JsonPrimitive;
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import com.google.gson.TypeAdapter;
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import com.google.gson.TypeAdapterFactory;
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import com.google.gson.internal.Streams;
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import com.google.gson.reflect.TypeToken;
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import com.google.gson.stream.JsonReader;
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import com.google.gson.stream.JsonWriter;
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/**
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* Adapts values whose runtime type may differ from their declaration type. This
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* is necessary when a field's type is not the same type that GSON should create
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* when deserializing that field. For example, consider these types:
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* <pre> {@code
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* abstract class Shape {
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* int x;
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* int y;
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* }
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* class Circle extends Shape {
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* int radius;
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* }
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* class Rectangle extends Shape {
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* int width;
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* int height;
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* }
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* class Diamond extends Shape {
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* int width;
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* int height;
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* }
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* class Drawing {
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* Shape bottomShape;
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* Shape topShape;
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* }
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* }</pre>
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* <p>Without additional type information, the serialized JSON is ambiguous. Is
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* the bottom shape in this drawing a rectangle or a diamond? <pre> {@code
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* {
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* "bottomShape": {
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* "width": 10,
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* "height": 5,
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* "x": 0,
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* "y": 0
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* },
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* "topShape": {
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* "radius": 2,
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* "x": 4,
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* "y": 1
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* }
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* }}</pre>
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* This class addresses this problem by adding type information to the
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* serialized JSON and honoring that type information when the JSON is
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* deserialized: <pre> {@code
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* {
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* "bottomShape": {
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* "type": "Diamond",
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* "width": 10,
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* "height": 5,
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* "x": 0,
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* "y": 0
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* },
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* "topShape": {
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* "type": "Circle",
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* "radius": 2,
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* "x": 4,
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* "y": 1
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* }
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* }}</pre>
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* Both the type field name ({@code "type"}) and the type labels ({@code
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* "Rectangle"}) are configurable.
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*
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* <h3>Registering Types</h3>
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* Create a {@code RuntimeTypeAdapterFactory} by passing the base type and type field
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* name to the {@link #of} factory method. If you don't supply an explicit type
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* field name, {@code "type"} will be used. <pre> {@code
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* RuntimeTypeAdapterFactory<Shape> shapeAdapterFactory
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* = RuntimeTypeAdapterFactory.of(Shape.class, "type");
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* }</pre>
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* Next register all of your subtypes. Every subtype must be explicitly
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* registered. This protects your application from injection attacks. If you
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* don't supply an explicit type label, the type's simple name will be used.
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* <pre> {@code
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* shapeAdapter.registerSubtype(Rectangle.class, "Rectangle");
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* shapeAdapter.registerSubtype(Circle.class, "Circle");
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* shapeAdapter.registerSubtype(Diamond.class, "Diamond");
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* }</pre>
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* Finally, register the type adapter factory in your application's GSON builder:
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* <pre> {@code
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* Gson gson = new GsonBuilder()
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* .registerTypeAdapterFactory(shapeAdapterFactory)
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* .create();
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* }</pre>
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* Like {@code GsonBuilder}, this API supports chaining: <pre> {@code
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* RuntimeTypeAdapterFactory<Shape> shapeAdapterFactory = RuntimeTypeAdapterFactory.of(Shape.class)
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* .registerSubtype(Rectangle.class)
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* .registerSubtype(Circle.class)
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* .registerSubtype(Diamond.class);
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* }</pre>
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*/
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public final class RuntimeTypeAdapterFactory<T> implements TypeAdapterFactory {
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private final Class<?> baseType;
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private final String typeFieldName;
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private final Map<String, Class<?>> labelToSubtype = new LinkedHashMap<String, Class<?>>();
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private final Map<Class<?>, String> subtypeToLabel = new LinkedHashMap<Class<?>, String>();
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private final boolean maintainType;
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private RuntimeTypeAdapterFactory(Class<?> baseType, String typeFieldName, boolean maintainType) {
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if (typeFieldName == null || baseType == null) {
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throw new NullPointerException();
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}
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this.baseType = baseType;
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this.typeFieldName = typeFieldName;
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this.maintainType = maintainType;
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}
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/**
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* Creates a new runtime type adapter using for {@code baseType} using {@code
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* typeFieldName} as the type field name. Type field names are case sensitive.
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* {@code maintainType} flag decide if the type will be stored in pojo or not.
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*/
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public static <T> RuntimeTypeAdapterFactory<T> of(Class<T> baseType, String typeFieldName, boolean maintainType) {
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return new RuntimeTypeAdapterFactory<T>(baseType, typeFieldName, maintainType);
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}
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/**
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* Creates a new runtime type adapter using for {@code baseType} using {@code
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* typeFieldName} as the type field name. Type field names are case sensitive.
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*/
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public static <T> RuntimeTypeAdapterFactory<T> of(Class<T> baseType, String typeFieldName) {
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return new RuntimeTypeAdapterFactory<T>(baseType, typeFieldName, false);
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}
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/**
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* Creates a new runtime type adapter for {@code baseType} using {@code "type"} as
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* the type field name.
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*/
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public static <T> RuntimeTypeAdapterFactory<T> of(Class<T> baseType) {
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return new RuntimeTypeAdapterFactory<T>(baseType, "type", false);
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}
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/**
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* Registers {@code type} identified by {@code label}. Labels are case
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* sensitive.
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*
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* @throws IllegalArgumentException if either {@code type} or {@code label}
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* have already been registered on this type adapter.
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*/
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public RuntimeTypeAdapterFactory<T> registerSubtype(Class<? extends T> type, String label) {
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if (type == null || label == null) {
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throw new NullPointerException();
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}
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if (subtypeToLabel.containsKey(type) || labelToSubtype.containsKey(label)) {
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throw new IllegalArgumentException("types and labels must be unique");
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}
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labelToSubtype.put(label, type);
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subtypeToLabel.put(type, label);
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return this;
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}
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/**
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* Registers {@code type} identified by its {@link Class#getSimpleName simple
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* name}. Labels are case sensitive.
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*
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* @throws IllegalArgumentException if either {@code type} or its simple name
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* have already been registered on this type adapter.
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*/
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public RuntimeTypeAdapterFactory<T> registerSubtype(Class<? extends T> type) {
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return registerSubtype(type, type.getSimpleName());
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}
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public <R> TypeAdapter<R> create(Gson gson, TypeToken<R> type) {
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if (type.getRawType() != baseType) {
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return null;
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}
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final Map<String, TypeAdapter<?>> labelToDelegate
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= new LinkedHashMap<String, TypeAdapter<?>>();
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final Map<Class<?>, TypeAdapter<?>> subtypeToDelegate
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= new LinkedHashMap<Class<?>, TypeAdapter<?>>();
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for (Map.Entry<String, Class<?>> entry : labelToSubtype.entrySet()) {
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TypeAdapter<?> delegate = gson.getDelegateAdapter(this, TypeToken.get(entry.getValue()));
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labelToDelegate.put(entry.getKey(), delegate);
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subtypeToDelegate.put(entry.getValue(), delegate);
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}
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return new TypeAdapter<R>() {
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@Override public R read(JsonReader in) throws IOException {
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JsonElement jsonElement = Streams.parse(in);
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JsonElement labelJsonElement;
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if (maintainType) {
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labelJsonElement = jsonElement.getAsJsonObject().get(typeFieldName);
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} else {
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labelJsonElement = jsonElement.getAsJsonObject().remove(typeFieldName);
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}
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if (labelJsonElement == null) {
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throw new JsonParseException("cannot deserialize " + baseType
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+ " because it does not define a field named " + typeFieldName);
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}
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String label = labelJsonElement.getAsString();
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@SuppressWarnings("unchecked") // registration requires that subtype extends T
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TypeAdapter<R> delegate = (TypeAdapter<R>) labelToDelegate.get(label);
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if (delegate == null) {
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throw new JsonParseException("cannot deserialize " + baseType + " subtype named "
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+ label + "; did you forget to register a subtype?");
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}
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return delegate.fromJsonTree(jsonElement);
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}
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@Override public void write(JsonWriter out, R value) throws IOException {
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Class<?> srcType = value.getClass();
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String label = subtypeToLabel.get(srcType);
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@SuppressWarnings("unchecked") // registration requires that subtype extends T
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TypeAdapter<R> delegate = (TypeAdapter<R>) subtypeToDelegate.get(srcType);
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if (delegate == null) {
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throw new JsonParseException("cannot serialize " + srcType.getName()
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+ "; did you forget to register a subtype?");
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}
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JsonObject jsonObject = delegate.toJsonTree(value).getAsJsonObject();
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if (maintainType) {
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Streams.write(jsonObject, out);
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return;
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}
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JsonObject clone = new JsonObject();
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if (jsonObject.has(typeFieldName)) {
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throw new JsonParseException("cannot serialize " + srcType.getName()
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+ " because it already defines a field named " + typeFieldName);
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}
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clone.add(typeFieldName, new JsonPrimitive(label));
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for (Map.Entry<String, JsonElement> e : jsonObject.entrySet()) {
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clone.add(e.getKey(), e.getValue());
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}
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Streams.write(clone, out);
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}
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}.nullSafe();
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}
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}
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