package com.google.gson;
import java.lang.reflect.Type;
/**
* <p>
* 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)}.
* </p>
*
* <p>
* 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}.
* </p>
*
* <pre>
* 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;
* }
* }
* </pre>
*
* <p>
* The default deserialization of {@code Id(com.foo.MyObject.class, 20L)} will require the Json
* string to be <code>{"clazz":com.foo.MyObject,"value":20}</code>. 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:
* </p>
*
* <pre>
* class IdDeserializer implements JsonDeserializer<Id>() {
* public Id deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context)
* throws JsonParseException {
* return new Id((Class)typeOfT, id.getValue());
* }
* </pre>
*
* <p>
* You will also need to register {@code IdDeserializer} with Gson as follows:
* </p>
*
* <pre>
* Gson gson = new GsonBuilder().registerTypeAdapter(Id.class, new IdDeserializer()).create();
* </pre>
*
* <p>
* 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 <T> 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<T> {
/**
* Gson invokes this call-back method during deserialization when it encounters a field of the
* specified type.
* <p>
* 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
* 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;
}