Extending David Chandler's ObjectifyGenericDao with interfaces

CodeSnippet1.java

import com.essaytagger.model.BasicUser;
import com.essaytagger.model.Essay;
import com.essaytagger.server.impl.ObjectifyGenericDAO;

// ...

ObjectifyGenericDAO<BasicUser> basicUserDao = new ObjectifyGenericDAO<BasicUser>();
BasicUser user = basicUserDao.get(userId);

ObjectifyGenericDAO<Essay> essayDao = new ObjectifyGenericDAO<Essay>();
Essay essay = essayDao.get(essayId);

CodeSnippet2.java

import com.essaytagger.model.BasicUser;
import com.essaytagger.model.Essay;
import com.essaytagger.server.IGenericDAO;
import com.essaytagger.server.impl.ObjectifyGenericDAO;

// ...

IGenericDAO<BasicUser> basicUserDao = new ObjectifyGenericDAO<BasicUser>();
IGenericDAO<Essay> essayDao = new ObjectifyGenericDAO<Essay>();

CodeSnippet3.java

import com.essaytagger.model.BasicUser;
import com.essaytagger.model.Essay;
import com.essaytagger.server.EssayTaggerDAOFactory;
import com.essaytagger.server.IGenericDAO;

// ...

IGenericDAO<BasicUser> basicUserDao = EssayTaggerDAOFactory.getBasicUserDAO();
IGenericDAO<Essay> essayDao = EssayTaggerDAOFactory.getEssayDAO();

CodeSnippet4.java

import com.essaytagger.model.BasicUser;
import com.essaytagger.model.Essay;
import com.essaytagger.server.EssayTaggerDAOFactory;
import com.essaytagger.server.EssayTaggerDAOFactory.IBasicUserDAO;
import com.essaytagger.server.EssayTaggerDAOFactory.IEssayDAO;

// ...

IBasicUserDAO basicUserDAO = EssayTaggerDAOFactory.getBasicUserDAO();
IEssayDAO essayDAO = EssayTaggerDAOFactory.getEssayDAO();

CodeSnippet5.java

import com.essaytagger.model.BasicUser;
import com.essaytagger.model.Comment;
import com.essaytagger.model.Essay;
import com.essaytagger.server.EssayTaggerManagerFactory;
import com.essaytagger.server.EssayTaggerManagerFactory.IBasicUserManager;
import com.essaytagger.server.EssayTaggerManagerFactory.IEssayManager;
import com.google.appengine.api.datastore.EntityNotFoundException;
import com.googlecode.objectify.Key;

// ...

// Retrieve the user
IBasicUserManager basicUserManager = EssayTaggerManagerFactory.getBasicUserManager();
BasicUser basicUser = basicUserManager.get(userId);

// Retrieve the essays that belong to this user
IEssayManager essayManager = EssayTaggerManagerFactory.getEssayManager();
List<Key<Essay>> essayKeys = essayManager.listKeysByProperty("owner", basicUserManager.getKey(userId));

// Iterate through and call one of the Extension methods
for (Key<Essay> key : essayKeys) {
	Essay essay = essayManager.get(key);
        Comment comment = new Comment("This is my comment");
        essayManager.addCommentToEssay(essay, comment);
}

EssayManager.java

public class EssayManager {
	IEssayDAO dao;

	public EssayManager() {
		dao = EssayTaggerDAOFactory.getEssayDAO();
	}
	
	public delete(Essay essay) {
		// Do something important first
		// ...
		
		// Then make the pass-through call
		dao.delete(essay)
	}
	
	public update(Essay essay) {
		// Nothing special to do
		dao.update(essay);
	}

	// And on and on for all the other basic operations
	// ...

EssayTaggerDAOFactory-v1.java

package com.essaytagger.server;

import com.essaytagger.model.BasicUser;
import com.essaytagger.model.Essay;
import com.essaytagger.server.impl.ObjectifyGenericDAO;
import com.googlecode.objectify.ObjectifyService;

public class EssayTaggerDAOFactory {

	static {
		ObjectifyService.register(BasicUser.class);
		ObjectifyService.register(Essay.class);
	}

	// Static-only usage pattern
	protected EssayTaggerDAOFactory() {}
	
	public static IGenericDAO<BasicUser> getBasicUserDAO() {
		return new ObjectifyGenericDAO<BasicUser>;
	}
	public static IGenericDAO<Essay> getEssayDAO() {
		return new ObjectifyGenericDAO<Essay>;
	}
}

EssayTaggerDAOFactory-v2.java

public class EssayTaggerDAOFactory {

	// Declare entity-specific versions of each Generic interface
	public interface IBasicUserDAO extends IGenericDAO<BasicUser> {}
	public interface IEssayDAO extends IGenericDAO<Essay> {}
	
	// Then use those interfaces as we declare entity-specific DAOs
	private static class BasicUserDAO extends ObjectifyGenericDAO<BasicUser> implements IBasicUserDAO {}
	private static class EssayDAO extends ObjectifyGenericDAO<Essay> implements IEssayDAO {}

	static {
		ObjectifyService.register(BasicUser.class);
		ObjectifyService.register(Essay.class);
	}

	// Static-only usage pattern
	protected EssayTaggerManagerFactory() {}
	
	public static IBasicUserDAO getBasicUserDAO() {
		return new BasicUserDAO();
	}
	public static IEssayDAO getEssayDAO() {
		return new EssayDAO();
	}
}