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
and 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 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 Id
will be deserialized into, and hence just want to
deserialize it from a Json string 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 { 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.
Modifier and Type | Method and Description |
---|---|
T |
deserialize(JsonElement json,
Type typeOfT,
JsonDeserializationContext context)
Gson invokes this call-back method during deserialization when it encounters a field of the
specified type.
|
T deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException
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 passing json
since that will cause an infinite loop (Gson will call your
call-back method again).
json
- The Json data being deserializedtypeOfT
- The type of the Object to deserialize toT
JsonParseException
- if json is not in the expected format of typeofT
Copyright © 2016. All Rights Reserved.