json.duby

import javax.servlet.http.HttpServlet
import com.google.appengine.ext.duby.db.Model

class Posts < Model
  property title, String
  property contents, Text
end

import com.google.json.JsonSerializer

class EntitySerializer; implements JsonSerializer
  def serialize(object, type, context)
    key = Entity(object).getKey
    context.serialize(key, key.getClass)
  end
end

import com.google.json.GsonBuilder

class JsonServlet < HttpServlet
  def doGet(request, response)
    response.setHeader('Content-Type', 'text/plain')
    response.getWriter.write(gson.toJson(Posts.all.run))
  end

  def gson
    @gson ||= begin
      klass = Entity.new('FooBar').getClass
      GsonBuilder.new.registerTypeAdapter(klass, EntitySerializer.new).create
    end
  end
end