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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 | * <p>Interface representing a custom deserializer for Json. You should write a custom | |
23 | * deserializer, if you are not happy with the default deserialization done by Gson. You will | |
24 | * also need to register this deserializer through | |
25 | * {@link GsonBuilder#registerTypeAdapter(Type, Object)}.</p> | |
26 | * | |
27 | * <p>Let us look at example where defining a deserializer will be useful. The {@code Id} class | |
28 | * defined below has two fields: {@code clazz} and {@code value}.</p> | |
29 | * | |
30 | * <pre> | |
31 | * public class Id<T> { | |
32 | * private final Class<T> clazz; | |
33 | * private final long value; | |
34 | * public Id(Class<T> clazz, long value) { | |
35 | * this.clazz = clazz; | |
36 | * this.value = value; | |
37 | * } | |
38 | * public long getValue() { | |
39 | * return value; | |
40 | * } | |
41 | * } | |
42 | * </pre> | |
43 | * | |
44 | * <p>The default deserialization of {@code Id(com.foo.MyObject.class, 20L)} will require the | |
45 | * Json string to be <code>{"clazz":com.foo.MyObject,"value":20}</code>. Suppose, you already know | |
46 | * the type of the field that the {@code Id} will be deserialized into, and hence just want to | |
47 | * deserialize it from a Json string {@code 20}. You can achieve that by writing a custom | |
48 | * deserializer:</p> | |
49 | * | |
50 | * <pre> | |
51 | * class IdDeserializer implements JsonDeserializer<Id>() { | |
52 | * public Id deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) | |
53 | * throws JsonParseException { | |
54 | * return new Id((Class)typeOfT, id.getValue()); | |
55 | * } | |
56 | * </pre> | |
57 | * | |
58 | * <p>You will also need to register {@code IdDeserializer} with Gson as follows:</p> | |
59 | * | |
60 | * <pre> | |
61 | * Gson gson = new GsonBuilder().registerTypeAdapter(Id.class, new IdDeserializer()).create(); | |
62 | * </pre> | |
63 | * | |
64 | * <p>New applications should prefer {@link TypeAdapter}, whose streaming API | |
65 | * is more efficient than this interface's tree API. | |
66 | * | |
67 | * @author Inderjeet Singh | |
68 | * @author Joel Leitch | |
69 | * | |
70 | * @param <T> type for which the deserializer is being registered. It is possible that a | |
71 | * deserializer may be asked to deserialize a specific generic type of the T. | |
72 | */ | |
73 | public interface JsonDeserializer<T> { | |
74 | ||
75 | /** | |
76 | * Gson invokes this call-back method during deserialization when it encounters a field of the | |
77 | * specified type. | |
78 | * <p>In the implementation of this call-back method, you should consider invoking | |
79 | * {@link JsonDeserializationContext#deserialize(JsonElement, Type)} method to create objects | |
80 | * for any non-trivial field of the returned object. However, you should never invoke it on the | |
81 | * the same type passing {@code json} since that will cause an infinite loop (Gson will call your | |
82 | * call-back method again). | |
83 | * | |
84 | * @param json The Json data being deserialized | |
85 | * @param typeOfT The type of the Object to deserialize to | |
86 | * @return a deserialized object of the specified type typeOfT which is a subclass of {@code T} | |
87 | * @throws JsonParseException if json is not in the expected format of {@code typeofT} | |
88 | */ | |
89 | public T deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) | |
90 | throws JsonParseException; | |
91 | } |