Java tutorial
/* * 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; /** * Interface representing a custom serializer for Json. You should write a custom serializer, if * you are not happy with the default serialization done by Gson. You will also need to register * this serializer through {@link com.google.gson.GsonBuilder#registerTypeAdapter(Type, Object)}. * * <p>Let us look at example where defining a serializer will be useful. The {@code Id} class * defined below has two fields: {@code clazz} and {@code value}.</p> * * <p><pre> * public class Id<T> { * private final Class<T> clazz; * private final long value; * * public Id(Class<T> clazz, long value) { * this.clazz = clazz; * this.value = value; * } * * public long getValue() { * return value; * } * } * </pre></p> * * <p>The default serialization of {@code Id(com.foo.MyObject.class, 20L)} will be * <code>{"clazz":com.foo.MyObject,"value":20}</code>. Suppose, you just want the output to be * the value instead, which is {@code 20} in this case. You can achieve that by writing a custom * serializer:</p> * * <p><pre> * class IdSerializer implements JsonSerializer<Id>() { * public JsonElement serialize(Id id, Type typeOfId, JsonSerializationContext context) { * return new JsonPrimitive(id.getValue()); * } * } * </pre></p> * * <p>You will also need to register {@code IdSerializer} with Gson as follows:</p> * <pre> * Gson gson = new GsonBuilder().registerTypeAdapter(Id.class, new IdSerializer()).create(); * </pre> * * <p>New applications should prefer {@link TypeAdapter}, whose streaming API * is more efficient than this interface's tree API. * * @author Inderjeet Singh * @author Joel Leitch * * @param <T> type for which the serializer is being registered. It is possible that a serializer * may be asked to serialize a specific generic type of the T. */ public interface JsonSerializer<T> { /** * Gson invokes this call-back method during serialization when it encounters a field of the * specified type. * * <p>In the implementation of this call-back method, you should consider invoking * {@link JsonSerializationContext#serialize(Object, Type)} method to create JsonElements for any * non-trivial field of the {@code src} object. However, you should never invoke it on the * {@code src} object itself since that will cause an infinite loop (Gson will call your * call-back method again).</p> * * @param src the object that needs to be converted to Json. * @param typeOfSrc the actual type (fully genericized version) of the source object. * @return a JsonElement corresponding to the specified object. */ public JsonElement serialize(T src, Type typeOfSrc, JsonSerializationContext context); }