Saliya's Blogs

The Sun's tutorial (http://java.sun.com/docs/books/tutorial/essential/concurrency/index.html) on concurrency with Java is a great place to start with multi-threading.

Have fun with threads :)

I was searching for a tool to scale images batch wise in Ubuntu and it seems that ImageMagick is just the one for it. Here's how you can get it working as well.

Step1: install ImageMagick

$ sudo apt-get install imagemagick

Step2: go to the images folder and type

$ mogrify -sample 1280 x 800 *.JPG

Here 1280 x 800 is the final size you want and *.JPG is the file set.

To get more info on command options, visit http://linuxuser32.wordpress.com/2007/06/16/batch-image-convert-scale-thumbnail-jpegs-pdf/

I recently came across this nice blog which had a post on locking the screen automatically. Anyway after seeing the comments I found it will be interesting to use Bluetooth to achieve this. I wanted to write some script on my own to get it done. Anyway as an initial step I tried BlueProximity which comes with Ubuntu. Here is a list of steps to get everything working.

1. Install blueproximity:
$ sudo apt-get install blueproximity

2. Pair up your computer with your phone using Bluetooth. You can use System -> Preferences -> Bluetooth to do so.

3. start blueproximity:
$ blueproximity &

You will see the blueproximity icon appearing on your system panel.

4. Configure blueproximity to suit your likings, i.e. the distance after which your screen will get locked, time duration, etc.

That's it.

Anyway it is not kicking unless I can write my own code :D

I started lecturing Data Structures and Algorithms to Level 2 students of the Dept. of Computer Science and Engineering, University of Moratuwa, Sri Lanka. Overall, it is a great experience and I really enjoy it. The bottom line that I understand is that it is only when you start teaching that you understand that you have to learn more ;)

If what comes out of the box does not suit your way of SOA requirements then try out WSO2 Carbon. The ebook (http://wso2.org/project/carbon/making_good_soa_great.pdf) says it all.

Ever tried accessing a shared folder in Vista from Ubuntu? Here are the simple step I followed.

For this example say your Vista user account is vista-pc and password is vista-pw. Also say the IP is 192.168.1.2

----Do the following in your Vista machine----
1. Start/Run secpol.msc
2. Open Local Policies/Security Options, find "Network Security: LAN Manager"
3. Change it to "Send LM & NTLM"
4. share the folder that you want (say movies)

---Do the following in your Ubuntu machine---
1. sudo apt-get install smbfs
2. sudo apt-get install smbclient
3. sudo mkdir /mnt/hd
4. sudo mount -t smbfs -o username=vista-pc,password=vista-pw //192.168.1.2/movies /mnt/hd

That's it :) You can now access the shared Vista folder from /mnt/hd

If you ever encounter an error saying Java heap is not enough, while building a project using Maven, the following content will help to get out of it. Thanks Charitha for finding this.

Sameera, Kalani, Isuru and I developed a Web services security module for the well known Apache Axi2 middleware. The existing security module, Rampart, has issues concerning performance. Therefore, our solution mainly focused on high performance. We used the code name Rampart2 to refer our project, though it is not part of Apache yet. The performance comparison of Rampart and Rampart2 can be found here.

I broke my spectacles and got a new pair from George Gooneratne Optometrists. Guess what? They have taken wrong measurements and I had to visit them again to replace the glasses with correct measurements. After spending about two hours at their lab I finally got my sparkling shiny spectacles. 

 

The day after I was playing basket ball at WSO2 when I got hit by the ball right on my face at a most unexpected time. I was actually catching my breath and I look up only to see something crashing on to me. The shiny new spectacles were broken into pieces and my nose got wounded. The wounds were not that serious and I was lucky not to bleed internally. I found the broken frame of my spectacles and thought, hey that's not too bad because I still have the frame to which I can get a pair of glasses fixed. I put all the pieces into my bag and came home. The next day I was getting ready to go and get new glasses fixed. I collected broken frame and believe me, one side arm was missing. What the hell? I told myself. I searched every possible place I could look into but came up with nothing. Hmm, that's life, I thought and went to optometrist and get a new spectacle fixed. 

 

The next day I was happy with my new spectacles and spent the day peacefully at WSO2. The entire day I was in a meeting and later in the evening I and the others were invited to dinner at an Indian restaurant. The food was okay, but it didn't sound right for me. The next morning I woke up to find that I am suffering from a very bad stomach ache. I spent the entire day at home unable to do anything. The medication came to effect only in the evening. Today is the second day of the very unpleasant "Digesting Error", and there is yet another day to go to end the week. I am expecting what next :)

I had couple of issues with IE and FF3 in Windows and I decided to give it a try with the Buzz: Google Chrome. Amazingly, it's pretty fast than I expected. The next thing I like about chrome is it's simplicity, no stupid buttons hanging all over your browser :). 

Comparing strings is bit tricky :) Say for an example you want to test a String reference against the literal "hello". In simple terms you have a String (say helloStr) and you want to see if the content of that is equals to "hello". You have two choices here,

1. helloStr.equals("hello")

2. "hello".equals(helloStr)

Both will do fine, but which is the better one? I've been using the second form but never thought of the difference (hmm, that's bad ;) anyway people do remember certain things bit later). In one of the code reviews at WSO2 it was revealed. The first form can lead to a Null pointer exception in the case when the helloStr is null. The second option will save you from this since the literal "hello" is not null always and you are invoking a method of a not null object. In this case even if the helloStr is actually null it doesn't matter because it'll only cause the program to check "hello" against null which results false.

If you are checking two String references then you have no option, but always try to invoke the equals() from the most probably not null reference.

Little things do matter :)

After installing FF2 because I was fed up with FF3 I had to setup the default browser in Thunderbird (see my previous post). I was happy after that but today I found that I cannot open any links from Pidgin messenger as well. Argh! I was unhappy again :-/

Fixing this issue, however, was pretty much easy ;) Open Pidgin, go to Tools --> Preferences --> Network. Then you can find a button saying Configure Browser. You'll get a tool window where you can set the command you want to execute in order to open up the browser. In my case FF2 can be started by issuing firefox-2 %s

Just that. It works fine :)

If you are searching for a tool to monitor messages that are exchanged between a client and a server, then Apache TCPMon is one of the best easy-to-use utilities available at zero cost. You can download three different flavors of this utility, i.e. standalone, IntelliJIDEA plug-in, and Eclipse plug-in. To get an in depth knowledge on how to use this nice tool see my blog post at wso2.org.

The following blog posts too give an insight into this tool.

http://charithaka.blogspot.com/2008/08/how-to-use-tcpmon-inside-eclipse.html
http://www.keith-chapman.org/2008/07/using-tcp-monitor-to-debug-web-service.html

I wanted to get the Internet connection to my notebook. The Internet facility is given by a CDMA service. So it's one machine only thing. That's bad because I need it to be given to two machines. Luckily I found this nice way of doing it from Dr. Sanjiva's blog. I'll try to find a pocket router similar to the one he has used and give it a go soon.

Anyway if you want to know about how to setup IP forwarding see the following links.

http://www.ducea.com/2006/08/01/how-to-enable-ip-forwarding-in-linux/
http://www.linuxforums.org/forum/linux-networking/64083-simple-ip-forwarding.html

I wanted to remove FF3 (Firefox 3) and install FF2 in Ubuntu because some of the web applications didn't work well in FF3. After doing a apt-get remove for FF3 and an apt-get install for FF2 I noticed that in Thunderbird when clicked on a link in a mail, will not open up a browser tab. So the hunt began :)

The solution was to tell Thunderbird the path of the browser to open. You need to create user.js file inside your ~/.mozilla-thunderbird/xxx.default/ (the xxx means any weird set of letters and numbers, e.g. 20art4c7). Type (or edit the path as to suit your browser) the following lines into that file and save it.

user_pref("network.protocol-handler.app.ftp","/usr/bin/firefox-2");
user_pref("network.protocol-handler.app.http","/usr/bin/firefox-2");
user_pref("network.protocol-handler.app.https","/usr/bin/firefox-2");

That's it :)

Apache Axiom, which is the popular open source StAX based XML infoset model, supports XPath out of the box. If you ever want to know how to use this feature, WSO2 Oxygentank has a very nice tutorial.

The tricky part is, how to work with Namespaces? To get an idea on to the matter consider the following XML document.



The following code fragment will retrieve the ns1:c1 element and the two ns2:color attributes of each element.

// root is the document
OMElement root = builder.getDocumentElement();

AXIOMXPath xpath = new AXIOMXPath("//a:c1");
xpath.addNamespace("a", "http://namespace1.com");
OMElement c1 = (OMElement)xpath.selectSingleNode(root);
System.out.println(c1);

xpath = new AXIOMXPath("//@b:color");
xpath.addNamespace("b", "http://namespace2.com");
List colors = xpath.selectNodes(root);
System.out.println(colors.get(0).getAttributeValue());
System.out.println(colors.get(1).getAttributeValue());

The important line in this code is the xpath.addNamespace(prefix, uri) method. This prefix doesn't have to be the exact prefix used in the actual document (which in fact is not known in most cases).

That's it, have fun with Axiom :)

In one of my previous posts I mentioned how to setup ATI X1300 graphics card in Ubuntu Gusty. Recently I installed Ubuntu Hardy because Gusty came up with couple of bugs. Unfortunately I had to set up my graphics card again :(

So I tried with the Unofficial ATI Wiki and it worked just as expected. Try method 2 mentioned here.

The great news is hibernation works with it :)

Recently one of my friends wanted to get the string contained in a ByteArrayInputStream in Java. The method do this was bit tricky and I thought it'd be nice to share it.

ByteArrayInputStream bais = // get your ByteArrayInputStream instance

int length = bais.available();
byte [] buff = new byte[length];
bais.read(buff);

That's it!!

The university life ended last Wednesday (7th May) and it was time to move into my first job in life :)

I joined WSO2 Inc. on 12th May and it has been few busy days until today :). I am waiting for some build to complete and thought to jump in and blog on this.

I feel life has changed a bit compared with the life at the university, yet it is the same old me sitting in front of the computer :)