The Gson project is a Java library developed by Googler for converting Java Objects for data-interchange using JSON, and vice versa.
Gson can work with arbitrary Java objects including pre-existing objects, even if you don't have access to the source code. Gson also supports Generics, unlike most other similar Java-to-JSON technologies.
Gson is supported natively by Android 3.x onwards - here's a good place to start
You might also want to check out Jackson JSON parser + JSON generator which purports to be meaner and leaner.
Scribbled by Ian