JSONObjectSerialization is a project mainly written in Java, it's free.
Simple examples for JSON objects serialization on android JSONObjectInputStream and JSONObjectOutputStream
An example for serializing and deserializing objects from / to JSON string on Android OS.
See this blog post for more informaton: http://blogs.msdn.com/b/dimast/archive/2011/07/04/serializing-de-serializing-object-to-from-json-string-on-android-os.aspx