/* * 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;import java.lang.reflect.Type;/** * <p>Interface representing a custom deserializer for Json. You should write a custom * deserializer, if you are not happy with the default deserialization done by Gson. You will * also need to register this deserializer through * {@link GsonBuilder#registerTypeAdapter(Type, Object)}.</p> * * <p>Let us look at example where defining a deserializer will be useful. The {@code Id} class * defined below has two fields: {@code clazz} and {@code value}.</p> * * <pre> * public class Id&lt;T&gt; { *   private final Class&lt;T&gt; clazz; *   private final long value; *   public Id(Class&lt;T&gt; clazz, long value) { *     this.clazz = clazz; *     this.value = value; *   } *   public long getValue() { *     return value; *   } * } * </pre> * * <p>The default deserialization of {@code Id(com.foo.MyObject.class, 20L)} will require the * Json string to be <code>{"clazz":com.foo.MyObject,"value":20}</code>. Suppose, you already know * the type of the field that the {@code Id} will be deserialized into, and hence just want to * deserialize it from a Json string {@code 20}. You can achieve that by writing a custom * deserializer:</p> * * <pre> * class IdDeserializer implements JsonDeserializer&lt;Id&gt;() { *   public Id fromJson(JsonElement json, Type typeOfT, JsonDeserializationContext context) *       throws JsonParseException { *     return (Id) new Id((Class)typeOfT, id.getValue()); *   } * </pre> * * <p>You will also need to register {@code IdDeserializer} with Gson as follows:</p> * * <pre> * Gson gson = new GsonBuilder().registerTypeAdapter(Id.class, new IdDeserializer()).create(); * </pre> * * @author Inderjeet Singh * @author Joel Leitch * * @param <T> type for which the deserializer is being registered. It is possible that a * deserializer may be asked to deserialize a specific generic type of the T. */public interface JsonDeserializer<T> {  /**   * Gson invokes this call-back method during deserialization when it encounters a field of the   * specified type.   * <p>In the implementation of this call-back method, you should consider invoking   * {@link JsonDeserializationContext#deserialize(JsonElement, Type)} method to create objects   * for any non-trivial field of the returned object. However, you should never invoke it on the   * the same type passing {@code json} since that will cause an infinite loop (Gson will call your   * call-back method again).   *   * @param json The Json data being deserialized   * @param typeOfT The type of the Object to deserialize to   * @return a deserialized object of the specified type typeOfT which is a subclass of {@code T}   * @throws JsonParseException if json is not in the expected format of {@code typeofT}   */  public T deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context)      throws JsonParseException;}