There is a question here. If I design my system in an object oriented way, why I need to store data in a relational database. You design your data model and then you need the overhead of some ORM to store your “objects” in the table. ORM libraries carries a cost. The library that I am using run extensive reflection calls and annotation parsing to compose SQL queries from my data model. It’s superb. Creates a lot of ease for me in handling with database. But it’s a layer itself and has its own cost in terms of performance.

Working in the systems tightly designed to work with RDBMS has made it difficult for me to think my data model independent of any database where I am not going to use joins and a lot of tables etc. I am talking about NoSQL databases. I believe now its a controversy to design your object oriented system and gluing with a relational database. I just want to store my data. Why I need to solve the puzzles of normalization, indexes and other totally DBA related stuff. Where as I am just a web programmer. I just want the simplification of my application data storage. For this I need to change my perspective of designing the system from RDBMS to NoSQL. It’s challenging.

Because I am a JDBC addict.

Picture credit: Simran Jindal’s blog

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3. HashMap vs Hashtable vs HashSet

MagicMatch match = Magic.getMagicMatch(getPromotionOptIn().getUpload(),false);
String mimeType = match.getMimeType();

You can download JMimeMagic lib from here.

JMimeMagic requires a dependency, that is Jakarata ORO. Jar can be downloaded from Apache archives.

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2. FUD: JDBC addiction and designing software for NoSQL
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I was missing this token and was wondering why I am getting HTTP 401 authentication failure. Well you can use following class to use Posterous API in Java.

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.Authenticator;
import java.net.PasswordAuthentication;
import java.net.URL;
import java.net.URLConnection;

public class AuthPosterous {
	private static BufferedReader data;

	  public static void authenticateHttpRequest(String webAddress, String username, String password) throws Exception {
	      Authenticator.setDefault(new MyAuthenticator(username, password));
	      URL url = new URL(webAddress);
	      URLConnection connection = url.openConnection();
	      data = new BufferedReader( new InputStreamReader(connection.getInputStream()) );
	  }

	  public static String readHttpRequest() throws Exception {
	      StringBuilder builder = new StringBuilder();
	      for (String line = null; (line = data.readLine()) != null;) {
	          builder.append(line).append("\n");
	      }
	      return builder.toString();
	  }

	  protected static class MyAuthenticator extends Authenticator {
	      private String username, password;
	      public MyAuthenticator(String user, String pwd) {
	          username = user;
	          password = pwd;
	      }
	      protected PasswordAuthentication getPasswordAuthentication() { return new PasswordAuthentication(username, password.toCharArray()); }
	  }

	    public static void main (String arg[]){
	        try {
	        	String yourPosterousUsername= "<yourEmailAsUserName>", yourPassword = "<yourPassword>",
	        		theAPIURL="http://posterous.com/api/2/users/me?api_token=<get_API_Token_From_Posterous_Docs>";
	        	/* get your API token from http://posterous.com/api */
	            AuthPosterous.authenticateHttpRequest(theAPIURL, yourPosterousUsername,yourPassword);
	              String readData = AuthPosterous.readHttpRequest();
	              System.out.println(readData);
	            }catch (Exception e) {
	                e.printStackTrace();
	            }
	    }
	}

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1. Fetch Twitter friends or followers through REST API in Java
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Effective September 1, 2010, all Java, Oracle Solaris, MySQL, Open Office and Oracle Solaris Cluster certifications have been re-published and rebranded under the Oracle Certification Program. This change will not impact any of the exam objectives and with Oracle’s firm commitment to the growth of the program, these credentials will continue to be some of the highest recognized achievements in the industry.

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Lets take a scenario. You have an Interface DAO.java that has abstract methods. You have written separate implementation for it. Lets suppose for different databases. So we are going to use the implementation of this DAO in our Struts2 application.

DAO.java

package com.pakzilla;
public interface DAO {
public void save(Object o);
}

DAOOracle.java

package com.pakzilla;
public class DAOOracle implements DAO {

public void save(Object o) {
System.out.println("Oracle implementaion");
}
}

DAOMySQL.java

package com.pakzilla;
public class DAOMySQL implements DAO {

public void save(Object o) {
System.out.println("MySQL implementaion");
}
}

DAOService .java

package com.pakzilla;
public class DAOService {
private DAO dao;

public void setDao(DAO _dao){
this.dao = _dao;
}

public DAO getDao(){
return dao;
}

public void saveRecord(Object o){
dao.save(o);
}
}

applicationContext.xml. You will put this file in JavaSource. So it will become the part of your classpath.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http://www.springframework.org/dtd/spring-beans.dtd">
<beans>

<bean id="daoOracle" class="com.pakzilla.DAOOracle" />
<bean id="daoMysql"   class="com.pakzilla.DAOMySQL"/>

<bean id="daoService" class="com.pakzilla.DAOService">
<property name="dao">
<!-- swith the daos here -->
<ref local="daoMysql"/>
</property>
</bean>
</beans>

Add following in web.xml. You see we are using classpath prefix with applicationContext.xml. Because this file will be in our classpaths. And on server startup web.xml will load it.

<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>
classpath:applicationContext.xml
</param-value>
</context-param>

<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>

Somewhere in your Struts2 Action, where you want to insert the record.

ApplicationContext context =
       new ClassPathXmlApplicationContext("applicationContext.xml");
DAOService daoService = (DAOService) context.getBean("daoService");
daoService.saveRecord(<your object to save>);

You must have following jars in your classpath.

antlr-runtime-3.0.jar
commons-fileupload-1.2.1.jar
commons-io-1.3.2.jar
commons-logging-1.1.jar
freemarker-2.3.13.jar
junit-3.8.1.jar
ognl-2.6.11.jar
org.springframework.asm-3.0.0.M3.jar
org.springframework.beans-3.0.0.M3.jar
org.springframework.context-3.0.0.M3.jar
org.springframework.core-3.0.0.M3.jar
org.springframework.expression-3.0.0.M3.jar
org.springframework.web-3.0.0.M3.jar
org.springframework.web.servlet-3.0.0.M3.jar
spring.jar
struts2-convention-plugin-2.1.6.jar
struts2-core-2.1.6.jar
struts2-spring-plugin-2.1.6.jar
xwork-2.1.2.jar

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Its been several years people started developing UIs in Divs. Now no one is working on tables. But if you want to shift on developing UI in Div, you need a learning curve on CSS. So what happen here? It has increased the cost of your time to develop a web page. Unless you master yourself in CSS. Huh?

So being a Java developer, should I master myself in CSS things too. If I am an independent (solo performer) developer that want to develop some app. First thing that came in my mind is, what happen when people will hit view source button. And will it not increase my time to deliver a thing. What should I consider, the features in my application? or the fear of developing the web pages in divs?

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1. Programmer vs Developer vs Architect
2. How the mind of a web developer works?
3. Ten things every Java developer should know about UNIX

1-    Console class.
2-    NavigableSet and NavigableMap.
3-    Lower(int) and higher(int) function are added in Treeset collection.
4-    Polling method in TreeSet and TreeMap.
5-    TreeSet.descendingSet() and TreeMap.descendingMap().

Thanks to Bilal for discussing these points with me.

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I used JDOM to parse XML.

import java.io.ByteArrayInputStream;
import java.io.DataInputStream;
import java.net.URL;
import java.net.URLConnection;
import java.util.ArrayList;
import java.util.List;

import org.jdom.Document;
import org.jdom.Element;
import org.jdom.input.SAXBuilder;

public class Twt {

String urlFlwrs= "http://twitter.com/statuses/followers/YOUR_TWITTER_SCREEN_NAME.xml?cursor=";
String urlFrnds= "http://twitter.com/statuses/friends/YOUR_TWITTER_SCREEN_NAME.xml?cursor=";

List followers = new ArrayList();
long cursorCounter = -1;

public static void main(String[] args) {
long start = System.currentTimeMillis();
new Twt().readFollowFriends();
System.out.printf("Total Time: %d secs",
(System.currentTimeMillis() - start)/1000);
}

void readFollowFriends(){

try {
StringBuffer followersData = new StringBuffer();
// use urlFrnds as a parameter if you want to fetch friends
URL url = new URL(urlFlwrs+cursorCounter);
URLConnection urlConnection = url.openConnection();
DataInputStream dis = new DataInputStream(
urlConnection.getInputStream());
String inputLine;
while ((inputLine = dis.readLine()) != null) {
followersData.append(inputLine);
}

SAXBuilder builder = new SAXBuilder();
Document document = builder.build(new ByteArrayInputStream(
followersData.toString().getBytes()));

Element root = document.getRootElement();
Element usersElm = root.getChild("users");
Element nextCursor = root.getChild("next_cursor");
List users = usersElm.getChildren("user");

for (int c = 0; c < users.size(); c++) {
Element user = (Element) users.get(c);
Element name = user.getChild("name");
// now you have every thing, the information of a user
// here you can populate followers list
}

if (nextCursor != null){
cursorCounter = Long.parseLong(nextCursor.getText());

if (cursorCounter != 0)
readFollowFriends();
}
} catch (Exception e) {
e.printStackTrace();
}
}
}

But you will also get following HTTP 400 error. Due to API limits by Twitter. For this we want to whitelist ourself.

java.io.IOException: Server returned HTTP response code: 400 for URL: http://twitter.com/statuses/followers/YOUR_TWITTER_SCREEN_NAME.xml?cursor=-1
at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1133)
at Twt.readFollowFriends(Twt.java:32)
at Twt.main(Twt.java:22)
Total Time: 7 secs

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Read more on SAI home page:

All SAI members may purchase the $40 discount vouchers until March 31, 2010 at saic.educationservicesgroup.com/ and redeem the vouchers at Prometric testing centers through the expiration dates. The voucher instructions and expiration dates are sent via email when members purchase the vouchers.

After March 31, 2010, all SAI members may obtain 40% off discount vouchers by emailing: contact_sai@sun.com

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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.

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