The JsonSerializer.java Java example source code
/*
* 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> * 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>The default serialization of {@code Id(com.foo.MyObject.class, 20L)} will be
* <code>{"clazz":com.foo.MyObject,"value":20}. 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> * class IdSerializer implements JsonSerializer<Id>() {
* public JsonElement serialize(Id id, Type typeOfId, JsonSerializationContext context) {
* return new JsonPrimitive(id.getValue());
* }
* }
* </pre>
*
* <p>You will also need to register {@code IdSerializer} with Gson as follows:
* <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);
}
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