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1 | /* |
2 | * Copyright (C) 2008 Google Inc. | |
3 | * | |
4 | * Licensed under the Apache License, Version 2.0 (the "License"); | |
5 | * you may not use this file except in compliance with the License. | |
6 | * You may obtain a copy of the License at | |
7 | * | |
8 | * http://www.apache.org/licenses/LICENSE-2.0 | |
9 | * | |
10 | * Unless required by applicable law or agreed to in writing, software | |
11 | * distributed under the License is distributed on an "AS IS" BASIS, | |
12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | |
13 | * See the License for the specific language governing permissions and | |
14 | * limitations under the License. | |
15 | */ | |
16 | ||
17 | package com.google.gson; | |
18 | ||
19 | import java.lang.reflect.Type; | |
20 | ||
21 | /** | |
22 | * Interface representing a custom serializer for Json. You should write a custom serializer, if | |
23 | * you are not happy with the default serialization done by Gson. You will also need to register | |
24 | * this serializer through {@link com.google.gson.GsonBuilder#registerTypeAdapter(Type, Object)}. | |
25 | * | |
26 | * <p>Let us look at example where defining a serializer will be useful. The {@code Id} class | |
27 | * defined below has two fields: {@code clazz} and {@code value}.</p> | |
28 | * | |
29 | * <p><pre> | |
30 | * public class Id<T> { | |
31 | * private final Class<T> clazz; | |
32 | * private final long value; | |
33 | * | |
34 | * public Id(Class<T> clazz, long value) { | |
35 | * this.clazz = clazz; | |
36 | * this.value = value; | |
37 | * } | |
38 | * | |
39 | * public long getValue() { | |
40 | * return value; | |
41 | * } | |
42 | * } | |
43 | * </pre></p> | |
44 | * | |
45 | * <p>The default serialization of {@code Id(com.foo.MyObject.class, 20L)} will be | |
46 | * <code>{"clazz":com.foo.MyObject,"value":20}</code>. Suppose, you just want the output to be | |
47 | * the value instead, which is {@code 20} in this case. You can achieve that by writing a custom | |
48 | * serializer:</p> | |
49 | * | |
50 | * <p><pre> | |
51 | * class IdSerializer implements JsonSerializer<Id>() { | |
52 | * public JsonElement serialize(Id id, Type typeOfId, JsonSerializationContext context) { | |
53 | * return new JsonPrimitive(id.getValue()); | |
54 | * } | |
55 | * } | |
56 | * </pre></p> | |
57 | * | |
58 | * <p>You will also need to register {@code IdSerializer} with Gson as follows:</p> | |
59 | * <pre> | |
60 | * Gson gson = new GsonBuilder().registerTypeAdapter(Id.class, new IdSerializer()).create(); | |
61 | * </pre> | |
62 | * | |
63 | * <p>New applications should prefer {@link TypeAdapter}, whose streaming API | |
64 | * is more efficient than this interface's tree API. | |
65 | * | |
66 | * @author Inderjeet Singh | |
67 | * @author Joel Leitch | |
68 | * | |
69 | * @param <T> type for which the serializer is being registered. It is possible that a serializer | |
70 | * may be asked to serialize a specific generic type of the T. | |
71 | */ | |
72 | public interface JsonSerializer<T> { | |
73 | ||
74 | /** | |
75 | * Gson invokes this call-back method during serialization when it encounters a field of the | |
76 | * specified type. | |
77 | * | |
78 | * <p>In the implementation of this call-back method, you should consider invoking | |
79 | * {@link JsonSerializationContext#serialize(Object, Type)} method to create JsonElements for any | |
80 | * non-trivial field of the {@code src} object. However, you should never invoke it on the | |
81 | * {@code src} object itself since that will cause an infinite loop (Gson will call your | |
82 | * call-back method again).</p> | |
83 | * | |
84 | * @param src the object that needs to be converted to Json. | |
85 | * @param typeOfSrc the actual type (fully genericized version) of the source object. | |
86 | * @return a JsonElement corresponding to the specified object. | |
87 | */ | |
88 | public JsonElement serialize(T src, Type typeOfSrc, JsonSerializationContext context); | |
89 | } |