Interface JsonDeserializer<T>
-
- Type Parameters:
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>
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
GsonBuilder.registerTypeAdapter(Type, Object)
.Let us look at example where defining a deserializer will be useful. The
Id
class defined below has two fields:clazz
andvalue
.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
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 theId
will be deserialized into, and hence just want to deserialize it from a Json string20
. 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 { return new Id((Class)typeOfT, id.getValue()); }
You will also need to register
IdDeserializer
with Gson as follows:Gson gson = new GsonBuilder().registerTypeAdapter(Id.class, new IdDeserializer()).create();
New applications should prefer
TypeAdapter
, whose streaming API is more efficient than this interface's tree API.
-
-
Method Summary
All Methods Instance Methods Abstract Methods Modifier and Type Method Description T
deserialize(JsonElement json, java.lang.reflect.Type typeOfT, JsonDeserializationContext context)
Gson invokes this call-back method during deserialization when it encounters a field of the specified type.
-
-
-
Method Detail
-
deserialize
T deserialize(JsonElement json, java.lang.reflect.Type typeOfT, JsonDeserializationContext context) throws JsonParseException
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
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 passingjson
since that will cause an infinite loop (Gson will call your call-back method again).- Parameters:
json
- The Json data being deserializedtypeOfT
- The type of the Object to deserialize to- Returns:
- a deserialized object of the specified type typeOfT which is a subclass of
T
- Throws:
JsonParseException
- if json is not in the expected format oftypeofT
-
-