2 * Copyright (C) 2008 Google Inc.
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
8 * http://www.apache.org/licenses/LICENSE-2.0
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.
17 package com
.google
.gson
;
19 import java
.lang
.reflect
.Type
;
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>
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>
31 * public class Id<T> {
32 * private final Class<T> clazz;
33 * private final long value;
34 * public Id(Class<T> clazz, long value) {
38 * public long getValue() {
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
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());
58 * <p>You will also need to register {@code IdDeserializer} with Gson as follows:</p>
61 * Gson gson = new GsonBuilder().registerTypeAdapter(Id.class, new IdDeserializer()).create();
64 * <p>New applications should prefer {@link TypeAdapter}, whose streaming API
65 * is more efficient than this interface's tree API.
67 * @author Inderjeet Singh
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.
73 public interface JsonDeserializer
<T
> {
76 * Gson invokes this call-back method during deserialization when it encounters a field of the
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).
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}
89 public T
deserialize(JsonElement json
, Type typeOfT
, JsonDeserializationContext context
)
90 throws JsonParseException
;