I mentioned in the post: Google App Store Datastore that I make data persistent by making requests to a FrontController which forwards the request to an ApplicationController which calls the needed class which implements Interactor. This is important for several reasons: (1) It is more secure, there is only one servlet to access my server. (2) Because we can call any class using an ApplicationController and an Interactor.

The following is the code for each of these classes: FrontController

public class FrontController extends HttpServlet {
	public void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
		ApplicationController ac = new ApplicationController(req, resp); //calls ApplicationController

	public void doPost(HttpServletRequest req, HttpServletResponse resp) throws IOException {
		this.doGet(req, resp); //doing this will allow you to call the same method
                                                   //whether a developer uses GET or POST


public class ApplicationController {
	HashMap controls = new HashMap();

	private void putControl() { //Key is what the application will call, Class is the program to return
		controls.put("addfood", AddFood.class);//do this with all the classes you may need to call

	public ApplicationController(HttpServletRequest request, HttpServletResponse response) {
		String action = request.getParameter("a").toLowerCase();//in the url string, ?a=addfood&...

		Class aClass = controls.get(action);

		try {
			if (aClass != null) {
				Interactor anInteractor = (Interactor) aClass.newInstance();
				anInteractor.invoke(request, response);
		} catch (Exception e) {


import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public interface Interactor {
	void invoke(HttpServletRequest request, HttpServletResponse response);

Note: Classes that implement the Interactor must implement the invoke method. Method signature looks like public class AddFood implements Interactor

[...] of Use « Google App Engine (Java) FrontController, ApplicationController, and Interactor [...]
tuesdayDeveloper; » Blog Archive » Google App Engine Datastore on 2010-02-20 17:51:49.0