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.smartandroid.sa.json;

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 toJson(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>
 * 
 * @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);
}