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Explore the source code of the class JsonSerializer.java


/*
 * 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 [email protected] com.google.gson.GsonBuilder#registerTypeAdapter(Type, Object)}.
 *
 * 

Let us look at example where defining a serializer will be useful. The [email protected] Id} class * defined below has two fields: [email protected] clazz} and [email protected] value}.

* *

 * 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;
 *   }
 * }
 * 

* *

The default serialization of [email protected] Id(com.foo.MyObject.class, 20L)} will be * {"clazz":com.foo.MyObject,"value":20}. Suppose, you just want the output to be * the value instead, which is [email protected] 20} in this case. You can achieve that by writing a custom * serializer:

* *

 * class IdSerializer implements JsonSerializer<Id>() {
 *   public JsonElement serialize(Id id, Type typeOfId, JsonSerializationContext context) {
 *     return new JsonPrimitive(id.getValue());
 *   }
 * }
 * 

* *

You will also need to register [email protected] IdSerializer} with Gson as follows:

*
 * Gson gson = new GsonBuilder().registerTypeAdapter(Id.class, new IdSerializer()).create();
 * 
* *

New applications should prefer [email protected] TypeAdapter}, whose streaming API * is more efficient than this interface's tree API. * * @author Inderjeet Singh * @author Joel Leitch * * @param 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 { /** * Gson invokes this call-back method during serialization when it encounters a field of the * specified type. * *

In the implementation of this call-back method, you should consider invoking * [email protected] JsonSerializationContext#serialize(Object, Type)} method to create JsonElements for any * non-trivial field of the [email protected] src} object. However, you should never invoke it on the * [email protected] src} object itself since that will cause an infinite loop (Gson will call your * call-back method again).

* * @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); }