/* * Copyright (C) 2008 Google Inc. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package com.google.gson; import java.lang.reflect.Type; /** *
Interface representing a custom deserializer for JSON. You should write a custom * deserializer, if you are not happy with the default deserialization done by Gson. You will * also need to register this deserializer through * {@link GsonBuilder#registerTypeAdapter(Type, Object)}.
* *Let us look at example where defining a deserializer will be useful. The {@code Id} class * defined below has two fields: {@code clazz} and {@code value}.
* ** public class Id<T> { * private final Class<T> clazz; * private final long value; * public Id(Class<T> clazz, long value) { * this.clazz = clazz; * this.value = value; * } * public long getValue() { * return value; * } * } ** *
The default deserialization of {@code Id(com.foo.MyObject.class, 20L)} will require the
* JSON string to be {"clazz":"com.foo.MyObject","value":20}
. Suppose, you already know
* the type of the field that the {@code Id} will be deserialized into, and hence just want to
* deserialize it from a JSON string {@code 20}. You can achieve that by writing a custom
* deserializer:
* class IdDeserializer implements JsonDeserializer<Id> { * public Id deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) * throws JsonParseException { * long idValue = json.getAsJsonPrimitive().getAsLong(); * return new Id((Class) typeOfT, idValue); * } * } ** *
You will also need to register {@code IdDeserializer} with Gson as follows:
* ** Gson gson = new GsonBuilder().registerTypeAdapter(Id.class, new IdDeserializer()).create(); ** *
Deserializers should be stateless and thread-safe, otherwise the thread-safety * guarantees of {@link Gson} might not apply. * *
New applications should prefer {@link TypeAdapter}, whose streaming API
* is more efficient than this interface's tree API.
*
* @author Inderjeet Singh
* @author Joel Leitch
*
* @param In the implementation of this call-back method, you should consider invoking
* {@link JsonDeserializationContext#deserialize(JsonElement, Type)} method to create objects
* for any non-trivial field of the returned object. However, you should never invoke it on the
* same type passing {@code json} since that will cause an infinite loop (Gson will call your
* call-back method again).
*
* @param json The Json data being deserialized
* @param typeOfT The type of the Object to deserialize to
* @return a deserialized object of the specified type typeOfT which is a subclass of {@code T}
* @throws JsonParseException if json is not in the expected format of {@code typeofT}
*/
public T deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context)
throws JsonParseException;
}