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/*
* 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 type for which the deserializer is being registered. It is possible that a
* deserializer may be asked to deserialize a specific generic type of the T.
*/
public interface JsonDeserializer {
/**
* Gson invokes this call-back method during deserialization when it encounters a field of the
* specified type.
* 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;
}