gson-interface

This project allows a class to define its own Gson serialization and
deserialization by implementing a simple interface. It also solves the
common problem of wanting to leverage Gson's default serialization while
adding a special field. In order for it to work, it must be registered with
the Gson instance:

Gson gson = new GsonBuilder()
        .registerTypeAdapterFactory(new InterfaceAdapterFactory())
        .create();

Check out InterfaceExample.java for an illustrative example of usage.

Any class that wishes to serialize itself must implement
JsonSerialization<THIS_CLASS>, implementing the

public JsonElement toJsonTree(GsonContext context)

method. In the implementation of that method, a user can call
context.toJsonTree(obj) and even context.thisToJsonTree(this). Note that
calling context.toJsonTree(this) will result in infinite recursion; that is
the point of using the context.thisToJsonTree(this) method

Any class that wishes to have custom deserialization must implement
JsonDeserialization<DESERIALIZER>, where DESERIALIZER implements
JsonDeserializes<CLASS_TO_DESERIALIZE>. The deserializer has to have a
default constructor and it has to implement the 

CLASS_TO_DESERIALIZE fromJson(JsonElement json, GsonContext context)

method. In the implementation of that method, a user can call
context.fromJsonTree(json, objClass), context.thisFromJsonTree(json), or
even context.thisFromJsonTree(json, subclassOfCLASS_TO_DESERIALIZE). As with
toJsonTree, calling context.fromJsonTree(json, CLASS_TO_DESERIALIZE.class)
will result in infinite recursion; use context.thisFromJsonTree(json)
instead.

This code has been tested heavily against gson-2.1 and recently updated to
incorporate changes in gson-2.2.1.

This project came largely from a discussion on the google-gson issue
tracker: http://code.google.com/p/google-gson/issues/detail?id=400

The example classes (Drink and MixedDrink) came from a related disussion:
http://code.google.com/p/google-gson/issues/detail?id=43