JsonSerializer/Deserializer: Allow reflection-oriented implementations

[GoogleCodeExporter]

It would be nice to use the JsonSerializer interface (or something similar) on 
the class itself, rather than in a separate utility class which then needs to 
be registered as a type adapter.  In this manner, the interface would need to 
look like:

JsonElement serialize(JsonSerializationContext context)

, allowing the class to use the current object's state for serialization.  Gson 
could reflect prior to serializing and, if it implements this interface, 
delegate to it rather than do the normal class/field reflection.

A similar notion could be done for the deserialization side.  This would be 
similar to how Java serializable/externalizable mechanisms work.

Original issue reported on code.google.com by [email protected] on 2 Sep 2014 at 4:14

[Marcono1234]

With the com.google.gson.annotations.JsonAdapter annotation which was added in 2.3 (released 2014-08-11), this is already more convenient than having to register the adapters on the Gson instance.