First of all, you should never store passwords. Then why the heck am I writing this post? Okay, Let me rephrase the first sentence – You should never store passwords as plain text anywhere in your application. of course, for the obvious reasons. If you store passwords as plain text, in database or in a log file, then even Rajinikanth couldn’t save your application getting **cked.. I mean hacked. (Edit: btw, Rajinikanth is the Chuck Norris of India, if you are not aware of him)

Then what’s the right way to deal with the asterisks? You could use encryption. But if there’s a way to encrypt it, then there should be a way to decrypt it. So, encryption is also vulnerable to hacker’s attack.

Isn’t there a better solution to this? It’s there and its called as Password Hashing.

How password hashing works?

In hashing, you take a input string (in our case, a password), add a salt to the string, generate the hash value (using SHA-1 algorithm for example), and store the hash value in DB. For matching passwords while login, you do the same hashing process again and match the hash value instead of matching plain passwords and authenticate users.

Hashing is different from encryption. Because, encryption is two way, means that you can always decrypt the encrypted text to get the original text. But Hashing is one way, you can never get the original text from the hash value. Thus it gives more security than encryption.

To generate hash, you can make use of any hashing algorithms out there – MD5, SHA-1, etc. Before generating a hash, adding a salt to the password will give added security. Salt is nothing but a simple text that is known only to you/your application. It can be “zebra” or “I’mGod” or anything you wish.

Below, I’m giving a Java example of how to do password hashing in an login module.

Password hashing example in Java

This is simple example containing two methods – signup() and login(). As their names suggest, signup would store username and password in DB and login would check the credentials entered by user against the DB. Let’s dive into the code.

package com.sandbox;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.HashMap;
import java.util.Map;

public class PasswordHashingDemo {

	Map<String, String> DB = new HashMap<String, String>();
	public static final String SALT = "my-salt-text";

	public static void main(String args[]) {
		PasswordHashingDemo demo = new PasswordHashingDemo();
		demo.signup("john", "dummy123");

		// login should succeed.
		if (demo.login("john", "dummy123"))
			System.out.println("user login successfull.");

		// login should fail because of wrong password.
		if (demo.login("john", "blahblah"))
			System.out.println("User login successfull.");
		else
			System.out.println("user login failed.");
	}

	public void signup(String username, String password) {
		String saltedPassword = SALT + password;
		String hashedPassword = generateHash(saltedPassword);
		DB.put(username, hashedPassword);
	}

	public Boolean login(String username, String password) {
		Boolean isAuthenticated = false;

		// remember to use the same SALT value use used while storing password
		// for the first time.
		String saltedPassword = SALT + password;
		String hashedPassword = generateHash(saltedPassword);

		String storedPasswordHash = DB.get(username);
		if(hashedPassword.equals(storedPasswordHash)){
			isAuthenticated = true;
		}else{
			isAuthenticated = false;
		}
		return isAuthenticated;
	}

	public static String generateHash(String input) {
		StringBuilder hash = new StringBuilder();

		try {
			MessageDigest sha = MessageDigest.getInstance("SHA-1");
			byte[] hashedBytes = sha.digest(input.getBytes());
			char[] digits = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
					'a', 'b', 'c', 'd', 'e', 'f' };
			for (int idx = 0; idx < hashedBytes.length; ++idx) {
				byte b = hashedBytes[idx];
				hash.append(digits[(b & 0xf0) >> 4]);
				hash.append(digits[b & 0x0f]);
			}
		} catch (NoSuchAlgorithmException e) {
			// handle error here.
		}

		return hash.toString();
	}

}

So, that’s it. I guess the above code is self explanatory. Do let me know in case you have any doubts.

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I hardly got ay response for my question about custom search engine to search only in programming related websites. I asked this because, at times I felt that I have been spending more time in Google search result pages than in the actual pages itself.

As you must be knowing, Google relies on PageRank and people know how to play around with PageRank. So, I usually get less relevant results on top of the ones which has more authentic data. Apart from this, I also wanted to reduce the noise in Google SERPs for my programming related queries. That was the reason why I needed a custom search engine.

Since no one replied (or there was no search engines like that) to my question, I created one for myself – CODERED. It’s a Google custom search engine which will only search in programming related websites. Not anything innovative – Just added my favorite websites to Google’s list (which you can achieve it using site:yoursitename filter too, manually!).

But which websites the CODERED searches? Well, currently there are few good websites that I have added to CODERED. If you would like to add to this list (you can recommend your blog too!), please give your suggestion here. Thanks!

Of course, please let me know your thoughts about this.

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Have you seen the infinite scrolling of content in some web pages? For example, in DZone.com when you scroll the page to the bottom, new links will be loaded automatically and it’ll give you the illusion that the page scrolls infinitely. Another good example is that Bing’s Image Search.

The technique is not hard to implement. With the use of a single servlet and JSP, we can implement a basic functionality with infinite scroll. Before dive into code details, have a look at this demo to get a feel of it: Infinite Scroll Demo

To implement this, we need a servlet which will serve the dynamic content and a JSP file which will have the UI and act as a client to receive the content. Below are the code for these two files. I’m leaving other common stuffs (like web.xml entry etc) to you.

Code for Servlet:

package com.vraa.demo;

import java.io.IOException;
import java.io.PrintWriter;

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

public class InfinitContentServlet extends HttpServlet {
    private static Integer counter = 1;

    protected void processRequest(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        PrintWriter out = response.getWriter();
        try {
            String resp = "";
            for (int i = 1; i <= 10; i++) {
                resp += "<p><span>"
                        + counter++
                        + "</span> This is the dynamic content served freshly from server</p>";
            }
            out.write(resp);
        } finally {
            out.close();
        }
    }

    @Override
    protected void doGet(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        processRequest(request, response);
    }

    @Override
    protected void doPost(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        processRequest(request, response);
    }
}

Code for JSP file:

<%@page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">

<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
        <title>Load content while scrolling - Infinite Scroll with Java and JQuery</title>
        <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js"></script>
        <style type="text/css">
            body{
                font-family:Arial;
                font-size:.93em;
            }
            #content-box{
                background-color:#FAFAFA;
                border:2px solid #888;
                height:300px;
                overflow:scroll;
                padding:4px;
                width:500px;
            }
            #content-box p{
                border:1px solid #EEE;
                background-color:#F0F0F0;
                padding:3px;
            }
            #content-box p span{
                color:#00F;
                display:block;
                font:bold 21px Arial;
                float:left;
                margin-right:10px;
            }
        </style>
        <script type="text/javascript">
            $(document).ready(function(){
                $contentLoadTriggered = false;
                $("#content-box").scroll(function(){
                    if($("#content-box").scrollTop() >= ($("#content-wrapper").height() - $("#content-box").height()) && $contentLoadTriggered == false)
                    {
                        $contentLoadTriggered = true;
                        $.get("infinitContentServlet", function(data){
                            $("#content-wrapper").append(data);
                            $contentLoadTriggered = false;
                        });
                    }

                });
            });
        </script>
    </head>
    <body>
        <h1>Demo page: Infinite Scroll with Java and JQuery</h1>
        <p>This page is a demo for loading new content while scrolling.</p>
        <p style="margin:20px 0;background-color:#EFEFEF;border:1px solid #EEE;padding:3px;">
        	Credits: Veera Sundar | <a href="http://veerasundar.com">veerasundar.com</a> | <a href="http://twitter.com/vraa">@vraa</a>
        </p>
        <div id="content-box">
            <div id="content-wrapper">
                <p><span>1</span>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Mauris ornare facilisis mollis. Etiam non sem massa, a gravida nunc. Mauris lectus augue, posuere at viverra sed, dignissim sed libero. </p>
                <p><span>2</span>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Mauris ornare facilisis mollis. Etiam non sem massa, a gravida nunc. Mauris lectus augue, posuere at viverra sed, dignissim sed libero. </p>
                <p><span>3</span>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Mauris ornare facilisis mollis. Etiam non sem massa, a gravida nunc. Mauris lectus augue, posuere at viverra sed, dignissim sed libero. </p>
                <p><span>4</span>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Mauris ornare facilisis mollis. Etiam non sem massa, a gravida nunc. Mauris lectus augue, posuere at viverra sed, dignissim sed libero. </p>
                <p><span>5</span>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Mauris ornare facilisis mollis. Etiam non sem massa, a gravida nunc. Mauris lectus augue, posuere at viverra sed, dignissim sed libero. </p>
            </div>
        </div>
    </body>
</html>

How it works?

The secret behind this is the scrolltop property. By checking this value we can determine whether the scrollbar has reached near to the bottom or not. If it reached, send an AJAX request to server to get more content and append it to the page. Look at the following two lines which does this:

 $contentLoadTriggered = false;
 $("#content-box").scroll(function(){
     if($("#content-box").scrollTop() >= ($("#content-wrapper").height() - $("#content-box").height()) && $contentLoadTriggered == false)
     {
         $contentLoadTriggered = true;
         $.get("infinitContentServlet", function(data){
             $("#content-wrapper").append(data);
             $contentLoadTriggered = false;
         });
     }

 });

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Sometime back, when Arun posted a Python version of Mars Rover problem, I tried the same in Java. Btw, if you haven’t heard about Mars Rover problem before, here’s the text for you (Ctrl+C & Ctrl+V’ed from Arun’s post).

Mars Rover problem:

A squad of robotic rovers are to be landed by NASA on a plateau on Mars.

This plateau, which is curiously rectangular, must be navigated by the rovers so that their on-board cameras can get a complete view of the surrounding terrain to send back to Earth.

A rover’s position and location is represented by a combination of x and y co-ordinates and a letter representing one of the four cardinal compass points. The plateau is divided up into a grid to simplify navigation. An example position might be 0, 0, N, which means the rover is in the bottom left corner and facing North.

In order to control a rover , NASA sends a simple string of letters. The possible letters are ‘L’, ‘R’ and ‘M’. ‘L’ and ‘R’ makes the rover spin 90 degrees left or right respectively, without moving from its current spot. ‘M’ means move forward one grid point, and maintain the same heading.

Assume that the square directly North from (x, y) is (x, y+1).

INPUT:

The first line of input is the upper-right coordinates of the plateau, the lower-left coordinates are assumed to be 0,0.

The rest of the input is information pertaining to the rovers that have been deployed. Each rover has two lines of input. The first line gives the rover’s position, and the second line is a series of instructions telling the rover how to explore the plateau.

The position is made up of two integers and a letter separated by spaces, corresponding to the x and y co-ordinates and the rover’s orientation.

Each rover will be finished sequentially, which means that the second rover won’t start to move until the first one has finished moving.

OUTPUT:

The output for each rover should be its final co-ordinates and heading.

INPUT AND OUTPUT

Test Input:

5 5
1 2 N
LMLMLMLMM
3 3 E
MMRMMRMRRM

Expected Output:

1 3 N
5 1 E

Solution in Java:

package marsrover;
public class Rover {
	public static final Integer N = 1;
	public static final Integer E = 2;
	public static final Integer S = 3;
	public static final Integer W = 4;
	Integer x = 0;
	Integer y = 0;
	Integer facing = N;
	public Rover() {
	}
	public void setPosition(Integer x, Integer y, Integer facing) {
		this.x = x;
		this.y = y;
		this.facing = facing;
	}
	public void printPosition() {
		char dir = 'N';
		if (facing == 1) {
			dir = 'N';
		} else if (facing == 2) {
			dir = 'E';
		} else if (facing == 3) {
			dir = 'S';
		} else if (facing == 4) {
			dir = 'W';
		}
		System.out.println(x + " " + y + " " + dir);
	}
	public void process(String commands) {
		for (int idx = 0; idx < commands.length(); idx++) {
			process(commands.charAt(idx));
		}
	}
	private void process(Character command) {
		if (command.equals('L')) {
			turnLeft();
		} else if (command.equals('R')) {
			turnRight();
		} else if (command.equals('M')) {
			move();
		} else {
			throw new IllegalArgumentException(
					"Speak in Mars language, please!");
		}
	}
	private void move() {
		if (facing == N) {
			this.y++;
		} else if (facing == E) {
			this.x++;
		} else if (facing == S) {
			this.y--;
		} else if (facing == W) {
			this.x--;
		}
	}
	private void turnLeft() {
		facing = (facing - 1) < N ? W : facing - 1;
	}
	private void turnRight() {
		facing = (facing + 1) > W ? N : facing + 1;
	}
	public static void main(String args[]) {
		Rover rover = new Rover();
		rover.setPosition(1, 2, N);
		rover.process("LMLMLMLMM");
		rover.printPosition(); // prints 1 3 N
		rover.setPosition(3, 3, E);
		rover.process("MMRMMRMRRM");
		rover.printPosition(); // prints 5 1 E
	}
}

After comparing my version with Arun’s version, all it came to my mind was, Joe Armstrong’s this quote:

“The problem with object-oriented languages is they’ve got all this implicit environment that they carry around with them. You wanted a banana but what you got was a gorilla holding the banana and the entire jungle.”

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If you remember, some time back I had released a small Java application called CSS Sorter that sorts the Cascading Style Sheet rules alphabetically. That application was developed based on Google’s App Engine Java platform. I took that project as a learning exercise to know more about Google App Engine development and it served well for that purpose.

However, the CSS Sorter tool was lacking few functionality and it had some bugs too (thanks to @sonnes for reporting one). I was holding the CSS sorter revamping plan for the past few weeks, mainly because the programming in my old laptop was a pathetic experience (hope my old laptop doesn’t read this post! ). Since now I’m a proud owner of a new powerful machine, I took up the revamping and here you go – the new CSS Sorter.

What did I fix:

• Fixed a bug, that removed the forward slashes in any URLs that are present in CSS.
• Added new ways to input CSS files. Now you can either Copy & Paste your CSS code or Upload a CSS File or Enter an URL which contains a CSS file.
• Redesigned the user interface.

I have few more plans also in my mind to develop. Hopefully I’ll release those soon.

Disclaimer: I would recommend you to take a backup of your CSS file, in case this tool mess up your CSS file after processing. But if you notice any bugs, please let me know so that I’ll fix it.

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Recently I attended an in-house session on “Eclipse tooling”. In that, the presenter shared an interesting information about the reason behind naming Eclipse as “Eclipse”. The history goes something like this:

Sun develops Java, Abstract Window Toolkit (AWT), Swing technologies =>   IBM wants to develop a extensible Java IDE/platform out of VisualAge => IBM evaluates both AWT and Swing for the new IDE’s UI => unsatisfied with both, IBM mixes both frameworks and develop Standard Widget Toolkit (SWT) => Sun has it’s own Java IDE, Netbeans, based on Swing => IBM open-sources the new IDE’s codebase and forms a foundation => Sun’s not joining the foundation => The new IDE project is named as Eclipse, meaning “shadowing the Sun”.

Pretty interesting, huh!

It’s a common game in team outings to ask about the meaning of person’s name. It looks like the same game could be extended to the software products as well.

And I would be really interested to know the reasons behind the names Python, Perl, SmallTalk, C etc. Any takers?

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Believe me, when I say Innovation (in the context of software development), you would have definitely thought about a company/product which is in it’s early stage, i.e. a startup. Off course, there are lots of large companies in the market with lots of resources (a.k.a. developers) and infrastructure and funding. But why couldn’t those companies make it to your mind, when you think about innovation?

The reason is simple – process.

Just compare the way the developers work at startup with their big companies counterparts. Startup developers mostly develop from scratch (or building on other open code), bringing in new ideas, brainstorming about different technical possibilities, trying to improvise their code/design – thus trying to be innovative. These fellas don’t need to follow any process. All are on their own to do things differently.

By process, I don’t mean the water fall or agile. The SDLC is more or less common between big companies/startups. But most big companies have one extra thing – their proprietary framework/tool and the process to develop on the framework/tool. So, when a developer join a big company,  he/she made to learn the company’s process. After this, there will be very less opportunity for the developer to think and do things differently. All he needs to do is follow some process and complete the work.

By saying this, I’m not devaluing the process. In my opinion, every big company MUST need some process in order to manage the large developer base. But, when the developers have the defined path (i.e. the process) in front of them, they mostly tend to take that path and miss to create new paths. In other words, the developers are becoming less innovative.

That’s why I say, when it comes to Innovation, startups rock and big companies, suck!

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This might interest any Java developer who uses Netbeans IDE from Sun. The Oracle + Sun merger does not raise the question of ‘what will happen to MySQL?’ alone. Because, along with the flagship database product, Oracle also has JDeveloper which conflicts with Netbeans IDE. Both software are used for Java development, but it seems like Netbeans has a widespread use than JDeveloper. So, after Oracle acquisition of Sun, will the database giant continue to develop Netbeans?

The Slide below, which seems to be from Oracle, could explain the Oracle’s take on Netbeans IDE.

Oracle's strategy for Netbeans IDE

In Summary, (if the above image is not displayed or not clear)

• Netbeans IDE support will be continued – more focus on Java EE6, Java ME, Scripting and dynamic languages.
• JDeveloper also will be continued as an IDE for Oracle Fusion Middleware.
• Oracle will continue it’s contribution to Eclipse as Strategic Member of Eclipse foundation.

It is clearly evident that Oracle can not halt the Netbeans IDE development. The IDE is already open sourced and if Oracle does halt the Netbeans development, it might have to face the negative feedback coming from the Netbeans developer community, for which Oracle may not be ready, yet.

So, what do you think about this move? You even concerned on this move or you just happy with your own copy of Eclipse ?

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I was working on an internal project that is used for archiving user’s blog posts. I released this application to an internal community and it was recieved quite well by the users. I made sure that the code was bug free, as far as I tested it and the code was working as expected with out any serious issues. But what is an application when there is no bug in it?

One user got back to me saying that the code successfully downloaded the blog posts but it failed during the index building process. The index building process was doing a simple string replacement, replacing a pattern with the list of archived posts links. I was using String.replaceAll() method for this. The user reported back that he is getting the exception: java.lang.IllegalArgumentException: Illegal group reference.

Initially I was clueless about why it is throwing the exception. But later when I debugged the code, I found that the exception was thrown because of the $ symbols that were present in the parameters to the replaceAll() method. To make it clear, have a look at the below code:

public static void main(String args[]) throws Exception {
    String template = "The user has spent amount in a day";
    String pattern = "amount";
    String output = template.replaceAll(pattern, "$ 100");
    System.out.println(output);
}

If you think that the above code will run without a issue and print “The use has spent $ 100 in a day”, then you are wrong. Here’s what this code will spit out:

Exception in thread "main" java.lang.IllegalArgumentException: Illegal group reference
        at java.util.regex.Matcher.appendReplacement(Matcher.java:713)
        at java.util.regex.Matcher.replaceAll(Matcher.java:813)
        at java.lang.String.replaceAll(String.java:2190)
        at demo.BugDemo.main(BugDemo.java:16)
Java Result: 1

The exception is thrown because the replacement string (i.e. “$ 100″) contains a $ symbol in it. And the Matcher.appendReplacement() class internally uses the $ symbol as a identifier for grouping. So inorder to avoid this, the $ symbol in the replacement string needs to be escaped using \\$. So after this fix, the correct code for the above program would be:

String output = template.replaceAll(pattern, "\\$ 100");

Hm.. perfect. This incident reminds me that debugging can teach us a lot than the actual development.

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In my last article about Aspect Oriented Programming (AOP), I explained how to use Spring AOP for profiling method execution time. When the article was posted in DZone, it got a comment from an user saying that

Profiling and logging seem to be to only imaginable AOP use cases.

But, I think it is not. Because AOP is an extensive area where a lot of examples can be shown as use cases of AOP. Here, “Use cases” are nothing but the cross cutting concerns in your application. That is, the functionalities that are used by many part of your application. Logging and Profiling are the best examples and can be easily explained for the cross cutting concerns. That is why in most of the AOP tutorials you can see a logging example or profiling.

Anyway, I tried to do some search on the various AOP cross-cutting concerns (i.e. the use cases) that can be found in an J2EE applications. Here is the list of them. Feel free to add if I’m missing/wrongly added something.

List of AOP Use Cases or Cross cutting concerns:

• Transaction Management – in an enterprise application, you can manage the transactional requests using AOP. For example, using the Around advice, you can wrap the request processing method and if the method fails for some reason, in your Advice, you can roll back the particular transaction.
• Access control or Security - in case you want to restrict the access to your method to a set of users, you can add these checks to the Before advice and verify the access credentials of the users before letting them to access your methods.
• Managing Quotas for your API - if your API is being used by many third party applications with predefined quotas, you can limit the access based the usage in your AOP advice. If the usage is below the allowed limit, the Advice can let the user to call the API or blocks it otherwise. This is something similar to the Google App Engine / Amazon services quota usages. But I’m not sure how Google/Amazon has implemented the quota limiting.
• Exception Wrapping – if you want to wrap a exception, thrown from your business methods, into a Common exception object and throw it to the top level layers, you can use After throwing advice to do the task. For example, if you want to wrap all the SQLExceptions into DAOLayerException object and throw it back to Service layer, instead of doing the exception wrapping in every single DAO method, you can implement the exception wrapping in an After throwing advice and it’s done.
• Logging and Profiling – off course, how can I leave these two? The evergreen examples(!) for the AOP.

I understand that this list is not an extensive one. So, if you have any more use cases to add this list, please leave a comment.

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