93 lines
3.5 KiB
Java
93 lines
3.5 KiB
Java
/*
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* Copyright (C) 2008 Google Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.google.gson;
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import java.lang.reflect.Type;
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/**
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* Interface representing a custom serializer for JSON. You should write a custom serializer, if
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* you are not happy with the default serialization done by Gson. You will also need to register
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* this serializer through {@link com.google.gson.GsonBuilder#registerTypeAdapter(Type, Object)}.
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*
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* <p>Let us look at example where defining a serializer will be useful. The {@code Id} class
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* defined below has two fields: {@code clazz} and {@code value}.</p>
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*
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* <pre>
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* public class Id<T> {
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* private final Class<T> clazz;
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* private final long value;
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*
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* public Id(Class<T> clazz, long value) {
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* this.clazz = clazz;
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* this.value = value;
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* }
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*
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* public long getValue() {
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* return value;
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* }
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* }
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* </pre>
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*
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* <p>The default serialization of {@code Id(com.foo.MyObject.class, 20L)} will be
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* <code>{"clazz":"com.foo.MyObject","value":20}</code>. Suppose, you just want the output to be
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* the value instead, which is {@code 20} in this case. You can achieve that by writing a custom
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* serializer:</p>
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*
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* <pre>
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* class IdSerializer implements JsonSerializer<Id> {
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* public JsonElement serialize(Id id, Type typeOfId, JsonSerializationContext context) {
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* return new JsonPrimitive(id.getValue());
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* }
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* }
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* </pre>
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*
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* <p>You will also need to register {@code IdSerializer} with Gson as follows:</p>
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* <pre>
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* Gson gson = new GsonBuilder().registerTypeAdapter(Id.class, new IdSerializer()).create();
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* </pre>
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*
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* <p>Serializers should be stateless and thread-safe, otherwise the thread-safety
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* guarantees of {@link Gson} might not apply.
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*
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* <p>New applications should prefer {@link TypeAdapter}, whose streaming API
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* is more efficient than this interface's tree API.
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*
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* @author Inderjeet Singh
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* @author Joel Leitch
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*
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* @param <T> type for which the serializer is being registered. It is possible that a serializer
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* may be asked to serialize a specific generic type of the T.
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*/
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public interface JsonSerializer<T> {
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/**
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* Gson invokes this call-back method during serialization when it encounters a field of the
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* specified type.
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*
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* <p>In the implementation of this call-back method, you should consider invoking
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* {@link JsonSerializationContext#serialize(Object, Type)} method to create JsonElements for any
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* non-trivial field of the {@code src} object. However, you should never invoke it on the
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* {@code src} object itself since that will cause an infinite loop (Gson will call your
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* call-back method again).</p>
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*
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* @param src the object that needs to be converted to Json.
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* @param typeOfSrc the actual type (fully genericized version) of the source object.
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* @return a JsonElement corresponding to the specified object.
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*/
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public JsonElement serialize(T src, Type typeOfSrc, JsonSerializationContext context);
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}
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