gson-comments/extras/src/main/java/com/google/gson/typeadapters/RuntimeTypeAdapter.java

/*
 * Copyright (C) 2011 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.typeadapters;

import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonParseException;
import com.google.gson.JsonPrimitive;
import com.google.gson.JsonSerializationContext;
import com.google.gson.JsonSerializer;
import java.lang.reflect.Type;
import java.util.LinkedHashMap;
import java.util.Map;

public final class RuntimeTypeAdapter<T>
    implements JsonSerializer<T>, JsonDeserializer<T> {

  private final Class<?> baseType;
  private final String typeFieldName;
  private final Map<String, Class<?>> labelToSubtype = new LinkedHashMap<String, Class<?>>();
  private final Map<Class<?>, String> subtypeToLabel = new LinkedHashMap<Class<?>, String>();

  public RuntimeTypeAdapter(Class<?> baseType, String typeFieldName) {
    this.baseType = baseType;
    this.typeFieldName = typeFieldName;
  }

  public static <T> RuntimeTypeAdapter<T> create(Class<T> c) {
    return new RuntimeTypeAdapter<T>(c, "type");
  }

  public static <T> RuntimeTypeAdapter<T> create(Class<T> c, String typeFieldName) {
    return new RuntimeTypeAdapter<T>(c, typeFieldName);
  }

  public void registerSubtype(Class<? extends T> type, String label) {
    if (subtypeToLabel.containsKey(type) || labelToSubtype.containsKey(label)) {
      throw new IllegalArgumentException("types and labels must be unique");
    }
    labelToSubtype.put(label, type);
    subtypeToLabel.put(type, label);
  }

  public void registerSubtype(Class<? extends T> type) {
    registerSubtype(type, type.getSimpleName());
  }

  public JsonElement serialize(T src, Type typeOfSrc, JsonSerializationContext context) {
    Class<?> srcType = src.getClass();
    String label = subtypeToLabel.get(srcType);
    if (label == null) {
      throw new IllegalArgumentException("cannot serialize " + srcType.getName()
          + "; did you forget to register a subtype?");
    }
    JsonElement serialized = context.serialize(src, srcType);
    final JsonObject jsonObject = serialized.getAsJsonObject();
    if (jsonObject.has(typeFieldName)) {
      throw new IllegalArgumentException("cannot serialize " + srcType.getName()
          + " because it already defines a field named " + typeFieldName);
    }
    JsonObject clone = new JsonObject();
    clone.add(typeFieldName, new JsonPrimitive(label));
    for (Map.Entry<String, JsonElement> e : jsonObject.entrySet()) {
      clone.add(e.getKey(), e.getValue());
    }
    return clone;
  }

  public T deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context)
      throws JsonParseException {
    JsonElement labelJsonElement = json.getAsJsonObject().remove(typeFieldName);
    if (labelJsonElement == null) {
      throw new JsonParseException("cannot deserialize " + typeOfT
          + " because it does not define a field named " + typeFieldName);
    }
    String label = labelJsonElement.getAsString();
    Class<?> subtype = labelToSubtype.get(label);
    if (subtype == null) {
      throw new JsonParseException("cannot deserialize " + baseType + " subtype named "
          + label + "; did you forget to register a subtype?");
    }
    @SuppressWarnings("unchecked") // registration requires that subtype extends T
    T result = (T) context.deserialize(json, subtype);
    return result;
  }
}