Now if user presses the refresh button or you want to get user information again from twitter any where in your application. You need to use the access token and this method twitter.setOAuthAccessToken(String1, String2). Because user has already been authenticated by Twitter. You can save this information in session.

HttpSession session = request.getSession();

twitter.setOAuthConsumer(Constants.CONSUMER_KEY,Constants.CONSUMER_SECRET);

if (session.getAttribute("aToken") == null){
	// request token
	String token = (String) session.getAttribute("token");
	String tokenSecret = (String)session.getAttribute("tokenSecret");
	AccessToken accessToken =
		twitter.getOAuthAccessToken(token, tokenSecret);
	twitter.setOAuthAccessToken(accessToken);

	// save the access token, that are different from request token
	session.setAttribute("aToken", accessToken.getToken());
	session.setAttribute("aTokenSecret", accessToken.getTokenSecret());

}else{
	// use the access token to authenticate user whenever you want
	twitter.setOAuthAccessToken((String)session.getAttribute("aToken"),
		(String)session.getAttribute("aTokenSecret"));
}
User user = twitter.verifyCredentials();

If you are also developing some app by using Twitter4J API on Google App Engine. Please give feedback on it.

Twitter4J Quick Tutorial: A quick tutorial on how to develop Twitter app by using Twitter4J on Google App Engine.

Google guys take some days to deliver the invitation. So be patience.

Wave is in development phase so not available to every one, except invitations. You can also request Google to deliver you. Read more about Google Wave.

He also tweeted about his last blog post on Sun.com, saying “Where Life Takes Me Next“.

Read the memo on AllThingsDigital.

After some browsing Oracle’s website I found they were some thing to say to Java developers community about continuing Sun Developer Network.

Sun.com now redirects to Oracle.com

FAQs for Sun Java developer community:

What will happen to Sun Developer Network, java.sun.com, and BigAdmin?

For the near future, all these sites will remain in their current form. We know that these resources are important, so you can continue to access them just as you always have at the same URLs and bookmarks. At some time, we foresee an integration of these sites into a newly redesigned and re-architected Oracle Technology Network, and we welcome your feedback about this process. We will make sure that any changes are communicated well in advance so that you will continue to have access to the tools and resources that you need.

And there are some other promises too about continuing Sun things.

I also found a Sun blogger saying good bye to blog.sun.com. Due to some Oracle policies that they can host only those blogs that targets to their products only not personal topics. You can read that blog post here.

A remarkable thing is I purchased the free retake voucher which is going to expire on June 2010. But I still didnt make even a single attempt. Ok thats all right. I am going to do it. I hope to appear for the successful first attempt in good marks.

I am not using any IDE for coding practice. I am using Notepad++ editor and command line Javac compilation. I want to get maximum of language fundamentals and want to think out of code completion feature.

Read them here:

• Cloud Computing
• Google App Engine for Java

You see todays date. OK, lets format it. 01/01/10

The combination of 0s and 1s.

So lets call the first day of 2010 is a binary friendly day. If we calculate the decimal of this binary we get 22. And we know binary has base 2.

Add these digits divide them with binary base and again you will get 2. ((2+2)/2)=2.

You guys can share your feedback if you read any book or any material on it.

I have presented following slides there. Also coded a basic sample application to show how to create and deploy new Java project on GAE. Which can send emails, how to use authentication by Google, and how to do database interaction. It was a very intresting topic for me to present. Participants also liked it.

Comments and feedback is welcomed on the presentation material from you guys.

I am using App Engine SDK version 1.2.18

Project name: engineplay
URL: http://engineplay.appspot.com

Project structure:

UserPrefs.java: The entity class

package com.engineplay.datastore.pojos;
import javax.persistence.Basic;
import javax.persistence.Entity;
import javax.persistence.EntityManager;
import javax.persistence.Id;
import com.engineplay.datastore.EMFService;
import com.google.appengine.api.users.User;

@Entity(name = "UserPrefs")
public class UserPrefs {
 @Id
 private String userId;
 private int donuts;
 @Basic
 private User user;

 public UserPrefs(String userId) {
 this.userId = userId;
 }

 /* TODO create getter and setters for above properties yourself */

 public static UserPrefs getPrefsForUser(User user) {
 UserPrefs userPrefs = null;
 EntityManager em = EMFService.get().createEntityManager();
 try {
 if (em.find(UserPrefs.class, user.getEmail()) == null) {

 userPrefs = new UserPrefs(user.getEmail());
 userPrefs.setUser(user);

 } else {
 userPrefs = em.find(UserPrefs.class, user.getEmail());
 }
 } finally {
 em.close();
 }
 return userPrefs;
 }

 public void save() {
 EntityManager em = EMFService.get().createEntityManager();
 try {
 em.persist(this);
 } finally {
 em.close();
 }
 }

 public void remove() {
 EntityManager em = EMFService.get().createEntityManager();
 try {
 UserPrefs userPrefs = em.find(UserPrefs.class, user.getEmail());
 em.remove(userPrefs);
 } finally {
 em.close();
 }
 }
}

EMFService.java: The class to create EntityManagerFactory instance.

package com.engineplay.datastore;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;

public class EMFService {
 private static final EntityManagerFactory emfInstance = Persistence
 .createEntityManagerFactory("transactions-optional");

 private EMFService() {
 }

 public static EntityManagerFactory get() {
 return emfInstance;
 }
}

LoginServlet.java

package com.engineplay.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.engineplay.datastore.pojos.UserPrefs;
import com.google.appengine.api.users.User;
import com.google.appengine.api.users.UserService;
import com.google.appengine.api.users.UserServiceFactory;

public class LoginServlet extends HttpServlet {

 public void doGet(HttpServletRequest req, HttpServletResponse resp)
 throws IOException {

 UserService userService = UserServiceFactory.getUserService();
 User user = userService.getCurrentUser();
 String navBar, form = null;
 int donuts = 0;
 if (user == null) {
 navBar = "<p>Welcome! <a href=\"" + userService.createLoginURL("/") +
 "\">Sign in or register</a> to customize.</p>";
 form = "";
 } else {
 UserPrefs userPrefs = UserPrefs.getPrefsForUser(user);

 if (userPrefs != null) {
 donuts = userPrefs.getDonuts();
 }
 navBar = "<p>Welcome, " + user.getEmail() + "! You can <a href=\"" +
 userService.createLogoutURL("/") +
 "\">sign out</a>.</p>";
 form = "<form action=\"/donuts\" method=\"post\">" +
 "<label for=\"donuts\">" +
 "Need more donuts?:" +
 "</label>" +
 "<input name=\"donuts\" id=\"donuts\" type=\"text\" size=\"4\" />" +
 " <input name=\"olddonuts\"  type=\"hidden\" value=\"" + donuts + "\" /> " +
 " <input name=\"userId\"  type=\"hidden\" value=\"" +user.getEmail()+ "\" /> " +
 "   <input type=\"submit\" value=\"  ADD  \" /><br><input type=\"submit\"  name =\"deleteBtn\" value=\"  DELETE ME!  \" />" +
 "</form>";

 }
 resp.setContentType("text/html");
 PrintWriter out = resp.getWriter();
 out.print("<html><head><title>Engine Play - Donuts</title</head><body>");
 out.println(navBar);
 if (donuts != 0)
 out.println("<p>Donuts you have: " + donuts + "</p>");
 else
 out.println("<p> No donuts you have   </p>");
 out.println(form);
 out.print("</body></html>");
 }
}

DonutsServlet.java

package com.engineplay.servlet;

import java.io.IOException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.engineplay.datastore.pojos.UserPrefs;
import com.google.appengine.api.users.User;
import com.google.appengine.api.users.UserService;
import com.google.appengine.api.users.UserServiceFactory;

public class DonutsServlet extends HttpServlet {

 public void doPost(HttpServletRequest req, HttpServletResponse resp)
 throws IOException {
 UserService userService = UserServiceFactory.getUserService();
 User user = userService.getCurrentUser();
 UserPrefs userPrefs = UserPrefs.getPrefsForUser(user);
 try {

 String deleteOpt = req.getParameter("deleteBtn");
 if (deleteOpt == null){
 int donuts = new Integer(req.getParameter("donuts")).intValue();
 int oldDonuts = new Integer(req.getParameter("olddonuts")).intValue();

 userPrefs.setDonuts(donuts + oldDonuts);
 userPrefs.save();
 }else{
 String userId = req.getParameter("userId");
 userPrefs.setUserId(userId);
 userPrefs.remove();
 }
 } catch (Exception e) {
 e.printStackTrace();
 }
 resp.sendRedirect("/Login");
 }
}

persistence.xml: Configuration file required for JPA

<?xml version="1.0" encoding="UTF-8" ?>
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:schemaLocation="http://java.sun.com/xml/ns/persistence

http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd"

 version="1.0">
 <persistence-unit name="transactions-optional">
 <provider>
 org.datanucleus.store.appengine.jpa.DatastorePersistenceProvider
 </provider>
 <properties>
 <property name="datanucleus.NontransactionalRead"
 value="true" />
 <property name="datanucleus.NontransactionalWrite"
 value="true" />
 <property name="datanucleus.ConnectionURL"
 value="appengine" />
 </properties>
 </persistence-unit>
</persistence>

web.xml

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE web-app PUBLIC
 "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
 "http://java.sun.com/dtd/web-app_2_3.dtd">

<web-app xmlns="http://java.sun.com/xml/ns/javaee" version="2.5">

 <servlet>
 <servlet-name>LoginServlet</servlet-name>
 <servlet-class>com.engineplay.servlet.LoginServlet</servlet-class>
 </servlet>
 <servlet>
 <servlet-name>DonutsServlet</servlet-name>
 <servlet-class>com.engineplay.servlet.DonutsServlet</servlet-class>
 </servlet>

 <servlet-mapping>
 <servlet-name>LoginServlet</servlet-name>
 <url-pattern>/Login</url-pattern>
 </servlet-mapping>
 <servlet-mapping>
 <servlet-name>DonutsServlet</servlet-name>
 <url-pattern>/donuts</url-pattern>
 </servlet-mapping>

 <welcome-file-list>
 <welcome-file>Login</welcome-file>
 </welcome-file-list>
</web-app>

Access the project here: http://engineplay.appspot.com