Oct 07

Using dCharts in Vaadin 7

I wanted a decent charting library to use in one of my FOSS projects which was created using Vaadin 7.1.2. Since Vaadin charts, the default choice for that purpose under Vaadin 7 needs a license to use it, I  switched my attention towards dCharts (https://vaadin.com/directory#addon/dcharts-widget). So I added the following maven dependency which is listed in the Vaadin site to my project and built it.

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But when I ran the project in the application server, I got the following error.

12:27:18,947 WARN [org.jboss.as.server.deployment] (MSC service thread 1-6) Class Path entry vaadin-server-7.0.7.jar in "/content/ui-0.1.war/WEB-INF/lib/dcharts-widget-1.7.0.jar" does not point to a valid jar for a Class-Path reference.

 12:27:18,951 WARN [org.jboss.as.server.deployment] (MSC service thread 1-6) Class Path entry vaadin-shared-7.0.7.jar in "/content/ui-0.1.war/WEB-INF/lib/dcharts-widget-1.7.0.jar" does not point to a valid jar for a Class-Path reference.

 12:27:18,957 WARN [org.jboss.as.server.deployment] (MSC service thread 1-6) Class Path entry vaadin-theme-compiler-7.0.7.jar in "/content/ui-0.1.war/WEB-INF/lib/dcharts-widget-1.7.0.jar" does not point to a valid jar for a Class-Path reference.

 12:27:18,961 WARN [org.jboss.as.server.deployment] (MSC service thread 1-6) Class Path entry vaadin-client-compiled-7.0.7.jar in "/content/ui-0.1.war/WEB-INF/lib/dcharts-widget-1.7.0.jar" does not point to a valid jar for a Class-Path reference.

 12:27:18,963 WARN [org.jboss.as.server.deployment] (MSC service thread 1-6) Class Path entry vaadin-themes-7.0.7.jar in "/content/ui-0.1.war/WEB-INF/lib/dcharts-widget-1.7.0.jar" does not point to a valid jar for a Class-Path reference.

 12:27:18,965 WARN [org.jboss.as.server.deployment] (MSC service thread 1-6) Class Path entry commons-lang3-3.1.jar in "/content/ui-0.1.war/WEB-INF/lib/dcharts-widget-1.7.0.jar" does not point to a valid jar for a Class-Path reference.

 12:27:18,966 WARN [org.jboss.as.server.deployment] (MSC service thread 1-6) Class Path entry commons-codec-1.7.jar in "/content/ui-0.1.war/WEB-INF/lib/dcharts-widget-1.7.0.jar" does not point to a valid jar for a Class-Path reference.

Looking at the error, it was evident that dCharts was looking at the wrong set of jars. So here’s what I did to overcome this problem.

First of all, checkout the dCharts code from http://source.dussan.org/dcharts . Then change the com.vaadin.vaadin value in the pom to 7.1.2 . Then rebuild the dCharts projects (mvn clean install).

Now open your Vaadin project. Go to the place in the pom where you added your dCharts dependency and replace it with the following.

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Now rebuild your Vaadin project (mvn clean install). Everything should work fine!.

p.s –

Don’t forget to add your chart to the UI using addComponent() method to make the chart visible!.

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Jan 19

A simple FAT32 bootloader written in assembly to boot from USB drives.

This is an assignment done by me for a second year project  in the university. The goal was to write a bootloader that can boot the given OS ( JOSH ) from a pen drive which is having FAT32 file system( We were supplied with a bootloader that could boot only from a FAT12 file system ). 


What this bootloader can do:


It can load the first file( which should be a file less than 4096 bytes) which is located in a USB drive with a FAT32 file system to the memory and hand over the execution to that program.


Download location:




Steps to use the Bootloader:


Included in the README file in gitHub. 



More information can be found in the pdf in the doc folder. 

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Jan 20

A basic guide to encryption -2

If you didn’t read the first part of this article you can read it by clicking here.

Ok, let’s continue our discussion on encryption. From this article onwards, I’m going to elaborate on types of encryption. Each of these types has something in common. That is the sender encrypts the set of data ( particularly a file) using a password or a key. When the receiver receives this encrypted file, he is able to use the file using a password/key that he posses. Encryption can be mainly divided in to three categories.

  1. Symmetric-key encryption
  2. Asymmetric-key encryption
  3. Hash functions

Symmetric-key encryption:

The sender and the receiver must have the same key/password. Or if the keys are not identical, they must be related to each other in a predefined specific manner.

Ex:- Sending a password protected zip file to a friend ( you protect the file with a password and tell the password to your friend).

This method is also called as a private-key method and it can be further devided in to two sub-categories.

  1. Stream cypher
  2. Block cypher

Stream cypher:

In a stream cypher, the file is converted bit by bit. For added security the actual message is combined with a keystream. The plaintext gets encrypted adding different cyphertext ( as discussed in the cypher section in the previous article).

Block cypher:

Block ciphers works on a set of bits. A set of bits gets transformed at a time.

Asymmetric-key encryption:

Also called a public key method. This method requires two types of keys,one is called the public-key and the other is called the private-key. The public-keys are distributed publicly. The private-keys only reside with the recipient. The sender who does the encryption should have the public-key which matches the receivers private-key. So when the sender encrypts the file using a public-key, only the receiver with the matching private-key can decrypt it.

Hash functions:

Hash encryption is an one way process and it cannot be reversed. So whats the use of it? Lets take an example from the real world to understand this.

The password for users in a linux operating system was used to be stored in the /etc/passwd file. But the password that was stored in this file was not the real password, but it’s hash value( generated using some unique algorithm-a hash function).When a user needs to login to the system, he enters his user name and password. The password that the user entered is fed to the hash function and the output from the hash function is compared with the hash value in the /etc/passwd file. If the two hash values match, the user was allowed to login to the system . The advantage of this method is the real password is never stored in the computer. So a hacker has no use of the file that contains the password( except if he is using a brute force method).

The aim of these two articles was to give you a basic understanding about cryptography and encryption. I hope you all got something out of it. All your comments are welcome…! .

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