| 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 | } |