Tech Diary

Move Web Application to Google App Engine

2011-06-29T17:11:00.000+10:00

Recently I started wondering how good the google app engine can support hosting web applications after I read the article Java Paas Shootout from IBM DW.

I gathered a few information about google app engine before i am going to make the move.

The first thing is the JRE class white list from google. This is the fundamental consulting list
http://code.google.com/appengine/docs/java/jrewhitelist.html

About how good is google app engine is compatible with some 3rd party libraries
http://groups.google.com/group/google-appengine-java/web/will-it-play-in-app-engine?pli=1

About how to do PDF generation on GAE
http://stackoverflow.com/questions/1765238/java-pdf-library-that-works-on-gae

About how to upload image to GAE
http://stackoverflow.com/questions/1513603/how-to-upload-and-store-an-image-with-google-app-engine-java

It seems the option is to use Blob store the store the uploaded stuff. see the following:
http://code.google.com/appengine/docs/java/blobstore/overview.html

DW: AIX commands you should not leave home without

2011-04-21T10:28:00.000+10:00

The AIX commands that tell the hardware/system information are quite handy: AIX commands you should not leave home without

WebSphere Application Server V7: Understanding Class Loaders

2011-03-25T14:57:00.000+11:00

This IBM redbook explains java class loading mechanism and it's related configuration in Websphere version 7.

Those who are confused by the weird java exception in websphere (ClassCastException, ClassNotFoundException and etc) are encouraged to read this article.

IBM Redbooks | WebSphere Application Server V7: Understanding Class Loaders

Dynamically Creating PDFs in a Web Application

2011-03-25T14:49:00.000+11:00

This article illustrates how to use iText to dynamically create PDFs in a web application.
Dynamically Creating PDFs in a Web Application - O'Reilly Media

In addition to iText, FOP is also an option.

Use find and grep on Linux

2011-02-23T15:11:00.003+11:00

Sometimes, we need to find out what files in a folder contains a given pattern. Under Linux, this can be done by the following command:

find  -name  -exec grep -l  {}\;

For example, the following command find all the files named "Root" under current folder and its sub folders that contains "domain":

find . -name Root -exec grep -l domain {}\;

Cloud computing service models From IBM DW

2011-02-22T15:33:00.001+11:00

The article from IBM DW talks about three levels of cloud computing services:

Infrastructure as a Service (IaaS),
Platform as a Service (PaaS),
Software as a Service (SaaS).

SaaS as the high level service brings the following benefits:

Increased speed of deployment
Increased user adoption
Reduced support requirements
Lowered cost of implementation and upgrades

More details from IBM DW web site:

Cloud computing service models: "In this three-part series find straightforward, real-world examples of cloud computing to help eliminate the confusion around the concept. Each article in this series covers one of the three service models of cloud computing, beginning with infrastructure as a service, then moving to platform as a service, and finally software as a service. After reading this series, cloud computing will feel like much more than simply a buzzword."

Hands on HTML5 Canvas from IBM DW

2011-02-20T12:14:00.002+11:00

Create great graphics with the HTML5 canvas: "Enhance your web pages with canvas, a simple HTML5 element that packs a

punch. Entice visitors to your site over and over again by taking advantage of

its flexibility and variety."

LaTeX GUI editors for latex file editing

2010-11-17T11:19:00.000+11:00

The following lists some of Latex gui editors that I know. They all run on Windows

WinEdt
"WinEdt™ (shareware) is a powerful and versatile ASCII editor and shell for MS Windows with a strong predisposition towards the creation of [La]TeX documents..."

WinShell
"WinShell is a free multilingual integrated development environment (IDE) for LaTeX and TeX. The program includes a text editor, syntax highlighting, project management, spell checking, a table wizard, BibTeX support, Unicode support, different toolbars and user configuration options. It is not a LaTeX system; an additional LaTeX package is required. "

LED -- LaTeX Editor
"LEd offers a project manager, powerful editor, integrated spellchecker and thesaurus, build-in DVI viewer, descriptive hints for LaTeX commands, code complete mechanism, word wrapping, code folding, multilingual environment, and more..." plus, it's free.

TexMakerX
"TexMakerX is a platform-independent LaTeX editor. It provides interactive spell checking, code folding and extended text navigation, while it also includes the features of the LaTeX editor Texmaker, like wizards, code completion and syntax highlighting". It's open source free software under GPL. It is actually a fork of another LaTeX editor: Texmaker.

Or you may want to use Emacs to do LaTex editing. The following links to some tips.
LaTeX, Emacs etc. for your PC

How to install additional perl modules on linux

2010-05-04T13:28:00.000+10:00

It can be as simple as this:

perl -MCPAN -e 'install '

Some interaction may be required to proceed the installation such as confirmation of installing some dependent modules.

It seems you need to have CPAN module installed first to be able to run this.
You can use yum (on fedora) or apt-get (on ubuntu) to install the module first.

More information on CPAN website.

How to turn wii into a media center

2010-04-21T17:15:00.001+10:00

There is a piece of small linux-based media center software called geexbox. This software has been ported to wii. That means that the popular video game console - wii - can be turned into a decent media center. Please do not expect it can play full HD movies, as the hardware of wii is quite low profile compared to ps3 or xbox 360. However, it does cope with various media formats (e.g., avi, mkv, wmv, rm, rmvb and etc).

The following is a few tips to install the geexbox media center to wii.

From the following link the information of geexbox for wii - the media center on wii - can be found (including the setup instruction).
http://geexboxforwii.sourceforge.net/content/

According to the setup instruction, to get geexbox work on wii, you need to install HBC (The Homebrew Channel) on wii first.

To install HBC, you need to use a hacking tool which can be found at:
http://bannerbomb.qoid.us/
There are two versions, and the v2 should be used if the wii system menu version is 4.2

The following video tells you how to check wii system menu:
http://www.youtube.com/watch?v=c-LIM_o_i4I

Post source code with syntax highlighted using wordpress plugin

2010-02-22T16:52:00.000+11:00

It seems blogger.com does not support syntax highlighting when posting source code (for example java source code). When viewing some posts at wordpress.com, i found it does have support for syntax highlighting, which is quite convenient for programmers to communicate coding idea clearly.

However, by default, the wordpress blogging software does not support source code syntax highlighting as i tried.So i assume that it should have some third-party plug-ins that support this syntax highlighting and formatting feature.

What i found is the following useful plug-in: SyntaxHighlighter Evolved
It seems that the wordpress.com also uses this plug-in. Actually, there are more similar plug-ins available. However, i may just try the "SyntaxHighlighter Evolved" one first to see if it satisfies my need.

JQuery UI Tabs: Updating URL with hash while clicking the tab

2010-02-12T16:28:00.001+11:00

JQuery UI Tabs is a popular choice of multi-tab implementation on a simple web page. It provides a bookmarkable URL for each tab like "http://www.mydomain.com/mypage#my-tab-1"

However, but default, when you click a tab, the hash part ("#my-tab-1" as in the previous example) will not be updated to the browser's address bar. So here's a problem: If a user clicks a link in the panel of the second tab and goes to another page, he/she can not return immediately to that tab when the "back" button of the browser is hit. Instead, he/she will see the default tab (which is normally the first tab). This is somewhat inconvenient to the user.

This problem is also described in the blog "Bookmarkable Tabs with jQuery UI". It uses another JQuery plugin "scrollTo" to resolve the problem. However, I think there can be a simple solution by using the tab event.

Here's my simple solution and it just solved the problem of updating the URL with the hash while clicking the tab. It updates the URL in the 'tabshow' event.

    $(function() {
       $("#tabs").tabs();
       $("#tabs").bind('tabsshow',function(event, ui) {
           window.location = ui.tab;
       })
    });

View the Unread Emails only in Gmail Inbox

2010-02-04T12:04:00.000+11:00

Days after days, it is easy to accumulate hundreds of unread messages out of thousands in the Gmail Indox for a lazy person like me.

Someday, I decided to do a cleaning to eliminate all the unread messages, either marking it read or deleting it. However, by default, Gmail does not seem to have a quick link to allow me to view all these unread emails in Inbox.

Fortunately, Gmail does provide a search term combination to list only unread messages in Inbox. The magic search term is "is:unread in:inbox"

More information on Gmail Search can be found at http://mail.google.com/support/bin/answer.py?hl=en&answer=7190

Useful reference management tools for academic paper writing

2009-07-07T17:21:00.000+10:00

Doing research often involves paper reading and writing. Referring to other papers is almost inevitable when writing papers. However, sometimes, the processing of writing a paper is frustrating just because you forget which exact papers to cite when it comes to the section of related works.

So reference paper management is quite important for the academic life. There are of course various tools that help to make the job easier. Here is a few tools i've used or encountered.

Endnote

Endnote is not a bad choice if you write papers using Microsoft word, as it has plugins for MS word. Most online research databases offer the export format that can be imported into Endnote, and you can also enter your owns manually. Notes or comments of the reference paper can also added to keep track of your thinking. It provides a lot of formatting styles to choose when it comes to the last bibliography section, which saves a lot of time for tedious formatting. However, you probably need a few time to play around with it before you master it.

Endnote is not free. The good thing is that students at some higher eduction institutes and universities can use it for free as the universities often have a volume license.

JabRef

When I started to use Latex to write the papers, Endnote seemed helpless. Hopefully, JabRef came into my sight after a few search.

"JabRef is an open source bibliography reference manager. The native file format used by JabRef is BibTeX, the standard LaTeX bibliography format. JabRef runs on the Java VM (version 1.5 or newer), and should work equally well on Windows, Linux and Mac OS X."

As most online research databases support BibTex exportation, so populating a JabRef database quite easy and straight forward. It also allows you to add links to the papers, so a single click can open the paper and allows you to have a second read. It offers integration to several tools. When I used WinEdt for the latex paper editing, the integration works quite good.

Zotero

When i came across Zotero, i've already been out of university for a while. So i haven't got a chance to play around it with real research tasks. But from what it says, it seems quite promising. So i've recommended it to my friends who are still doing fun researches in the universities.

Zotero is a free, easy-to-use Firefox extension to help you collect, manage, and cite your research sources. It lives right where you do your work—in the web browser itself.

Other tools

Of course, there are plenty other similar tools for this reference management tasks. You can find the more complete list and the comparison at
http://en.wikipedia.org/wiki/Comparison_of_reference_management_software

Personal Finance Software and online services for Money Management

2009-04-03T16:31:00.000+11:00

Use a piece of software or a online service to consolidate all your financial information may help you better understand your money.

Here is a list of personal finance software and online services that could help you find a suitable choice to manage your money.

A more detailed article on the personal finance 2.0 web applications could also be helpful.

Using __autoload function in PHP 5

2008-06-11T17:26:00.000+10:00

The magic function "__autoload" is a new feature of PHP version 5. When this function is defined, it will be triggered when php can not find the class it is calling from the explicit "require", "include" statements. The benefit of using this magic function can be as follows:

Improve performance: This lazy loading mechanism avoids loading unnecessary class files.
Central control of including class files: You don't have to write "include xxx", "include_once xxx", "require xxx", and "require_once xxx" in every file.
Encouraging naming convention for class name/files: the better way you name your classes and files, the easier for you to make the __autoload function.
Flexibility to relocate php class files: since file including is controlled centrally, it is very easy to change the path of the included class files. no need to change every files.

Here's one article that tells you how to write the __autoload function to improve the performance. And also some one argues that this __autoload function might be evil.

Configuring Tomcat Virtual Hosts and Making it Work with Apache

2008-02-27T17:09:00.000+11:00

This job contains two parts, which are the following:

Tomcat virtual hosts

Normally, deployment of web application under tomcat is quite easy. Just copy the 'war'ed application (for example app.war) to the webapps directory (e.g., /var/lib/tomcat5/webapps).

However, if there are multiple virtual hosts that are hosted by tomcat, this may not work. The following actions need to be taken:

1. Modify the server.xml (e.g., "/etc/tomcat5/server.xml" if you have tomcat installed via yum on Fedra Core 8, aka FC8) file to add virtual host in. The following is an example:

<host name="www.mydomain.com" appbase="/var/www/hosts/mydomain/public_html"
unpackWARs="true" autoDeploy="true"
xmlValidation="false" xmlNamespaceAware="false">

<Valve className="org.apache.catalina.valves.AccessLogValve"
directory="/var/www/hosts/mydomain/logs" prefix="mydoamin_access_log." suffix=".txt"
pattern="combined" resolveHosts="false"/>
</host>

NOTE: this section of configuration needs to be put in the RIGHT place in the file hiearachy (check the comments in the file). Otherwise, it will cause problem.

2. Put your web app (i.e., app.war) in the the directory indicated by "appBase" (here it is '/var/www/hosts/mydomain/public_html').

3. Restart tomcat (e.g., "/etc/init.d/tomcat5 restart") and access the web to test it (i.e., http://www.mydomain.com:8080/app)

Working with Apache

To allow users to access the web application without accessing 8080 port, Apache needs to be configured to work with tomcat. This actually requires a connector. By default in FC 8, proxy_ajp is used. It's quite easy to setup this connector. The following is an configuration example for a virtual host. All we need is to add a line.

<VirtualHost *:80>
ServerName www.mydomain.com
DocumentRoot /var/www/hosts/mydomain/public_html
ErrorLog /var/www/hosts/mydomain/logs/error_log
CustomLog /var/www/hosts/mydomain/logs/access_log combined
DirectoryIndex index.html index.htm index.php index.php4 index.php5
ProxyPass /app/ ajp://www.mydomain.com:8009/app/
...
</VirtualHost>

Java Regular Expression (regex): A Very Simple Example

2007-12-20T13:48:00.000+11:00

Here's a very simple example of using java builtin packages (java.util.regex) that deals with regular expression. I made this to remind me that using java regex is quite simple and easy.

Sun web site has more details of this java.util.regex package and regex patterns.

import java.util.regex.Matcher;

import java.util.regex.Pattern;

public class TestRegex {

/**

* @param args

*/

public static void main(String[] args) {

// a test input string

String input = "This is a test string.nThis is a second line.";

// first compile a pattern with multiple-line enabled

Pattern pn = Pattern.compile("(\w+)", Pattern.MULTILINE);

// then get a matcher from the input string

Matcher mr = pn.matcher(input);

// show group count (should be 1)

System.out.println("Group Count: " + mr.groupCount());

// print out all the words

while (mr.find()) {

System.out.println(mr.group(1));

}

}

}

Using Java Desktop API to Launch System Browser

2007-12-04T16:57:00.000+11:00

In Python, we have a module called "webbrowser" that allows us to open given URLs in most mainstream browsers (IE, Firefox, and etc).

Recently, I found Java SE 6 has added new APIs that support the similar function. The new added Desktop APIs are reflected through a class called "java.awt.Desktop". For example, the following code opens a url in the system default browser (without considering exceptions).

...
import java.awt.Desktop;
...
Desktop desktop = Desktop.getDesktop();
desktop.browse(new URI(''a_url"));
...

In addition to open urls in browsers, it also provides API that can also open files with their default associated applications. More detailed information and examples on this Desktop API can be found here:Using the Desktop API in Java SE 6

Making Linux (Fedora Core 8) as a Gateway and a DHCP Server

2007-11-22T14:55:00.000+11:00

Making Linux (Fedora Core 8) as a Gateway and a DHCP Server

Recently I configured a Linux computer as a gateway and a dhcp server for a friend. To prevent me from forgetting the things learned, I just make some notes here.

The main jobs involved are the configurations of the network interface cards (NICs), iptables, and dhcpd.

First, NICs.

Normally, we have two NICs on the Linux machine:

one connecting to the public internet via cable modem, DSL modem or whatever. We name it eth0;
the other connecting to an internal private network (usually a pub or a switch where all the internal computers are plugged in). We name it eth1.

We need to assign IPs and default gateways of the two NICs PROPERLY. Normally, they fall in different networks(?). eth1 is often given a private IP like "192.168.1.1".

Then, iptables.

Before setting up the iptables, ip forward should be enabled on this Linux machine. This can be done by add/change an entry in the file "/etc/sysctl.conf" to the following:

net.ipv4.ip_forward = 1

(This works on Fedora Core 7 and 8. I am not sure if other Linux distributions have the same configuration file.)

The "iptables" program is then configured to allow NAT. we need to enable computers behind the firewall (the linux machine) to access public internet transparently. For this requirement, SNAT is required. So the following rules are desirable:

# Forward all packets from eth1 (internal network) to eth0 (the public internet)

iptables -A FORWARD -i eth1 -o eth0 -j ACCEPT

# Forward packets that are part of existing and related connections from eth0 to eth1

iptables -A FORWARD -i eth0 -o eth1 -m state --state ESTABLISHED,RELATED -j ACCEPT

# Enable SNAT functionality on eth0. a.b.c.d are generally the ip of the eth0

iptables -A POSTROUTING -t nat -s 192.168.1.0/24 -o eth0 -j SNAT --to-source a.b.c.d

There is a Linux Example Fireware Script that provides more detailed description on how to configure the iptables for this function. Actually, we made our configuration based on it. And there are also some useful explanations on using Linux firewall at this web site: Linux Home Networking.

If we need to host a web server behind the firewall and allow people from the public internet to access it, I think we need to enable DNAT. I found the book "Linux Administration: A Beginner's Guide" (by Steve Shah and Wale Soyinka) has very nice figure illustrations on the two different situations (when to use SNAT or DNAT).

Finally, DHCP.

Configuring DHCP seems quite straightforward. DHCP service program should be installed. And its configuration file ("/etc/dhcpd.conf") should be properly composed as there are no default configurations in the conf file. We referred to this howto tutorial: "Configuring the DHCP Server" to get our job done.

Enabling N73 (English version) to display and input Chinese characters

2007-11-06T21:08:00.000+11:00

Enabling N73 (English version) to display and input Chinese characters

This is a downside point to buy a phone overseas. Although it was made in China, it doesn't have Chinese support (read/input or both) in most cases. And that happened to me when I bought a Nokia N73 phone in Australia.

It is annoying sometimes as all the messages and file names in Chinese can not be displayed properly, especially when i used my phone in my home country China.

So i persisted to look for a solution to this matter. And finally I got it.

First, enabling the display of Chinese characters.
Since the OS in Nokia N73 is symbian s60 3rd edition, which fully supports Unicode, I believe the cause of disability of display Chinese on my N73 is only the lack of proper fonts. After numerous searching and study, my belief turned out to be true, and I found the way to use additional fonts to display Chinese characters. Here's the trick:

1. Get some TTF fonts that have Chinese character supports. Here's a link (in Chinese) that has some fonts for download.
2. Rename the font files properly. The default font files in N73 (or maybe other s603rd) have the following names:
nosnr60.ttf = Nokia Sans S60 Regular
nssb60.ttf = Nokia Sans S60 SemiBold
nstsb60.ttf = Nokia Sans S60 TitleSmBd S60
S60ZDIGI.ttf = Series 60 ZDigi, just LCD digits 0-9 plus .:,;*?
So just use the corresponding names for the new font files.
3. Make sure folder "/resource/fonts" exists on the phone memory card (if not, just create it). put the font files in the folder.
4. Maybe a restart of the phone is required.

Then it's done. the phone can display Chinese in messages, media players, ....
More detailed information on changing fonts can be found here.

Some times you may still find messed characters in the phone media player when playing mp3 songs with Chinese titles. This is because the tags (ID3?) in mp3 files are not encoded in Unicode (UTF8), you can use tools like mp3tag to convert the tag info encoding (mostly from GBK or GB18030 to UTF8) before transferring mp3 files to the phone.

Then, enabling the input of Chinese characters.
This could be even simpler. Installing a Chinese input method would get it done. And fortunately, I found this A4 input method (in Chinese) works quite well on my N73, plus it has a free version for personal use. The drawback is that this method only works for composing messages. However, this is enough for me!

The above methods work quire well for my N73 phone. I hope this helps you if you have the similar situations. I think they are safer than some ROM reflashing methods that break the warranty conditions. However, I am not responsible if the methods cause any damage to your phone:)

Python: should I learn this language?

2007-03-14T15:25:00.000+11:00

Recently, I got interested in this new language: Python, partially because of an interesting screencast on web application development, which can be viewed from NASA's Jet Propulsion Laboratory.

The first question that came into my mind was: What are the features of this "script language" compared to some other script languages such as Perl and PHP.

Perl is a popular script language, which I learned a bit for a project. It's true that I felt uncomfortable with its code readability.

PHP is a language that I've got known for a long time and have used for several projects. It's a good language to make dynamic web pages. However, it's a shame that I sometime still forget to put $ before variables. This caused me a lot of debugging trouble when I used it at the very begining.

Then, the following article partially answered my question:
Why Python? from Linux Journal

So I've got more interested in Python...

latex table: packages for Multirow and multicolumn spanning

2006-09-25T15:03:00.000+10:00

Making table in latex is a tedious job for me. You have to code it manually to set different parameters for different styles you want. Never as straightforward as in Word.

I finnally find out that I can not do multiple column or multiple row spanning without additional packages. Fortunately, I read the following article, which quickly helped me out.

Anyway, you need the multirow package, that is, to put
\usepackage{multirow} in preamble of the latex file.

More details, refer to
Multirow and multicolumn spanning with latex tables

Html embedded WYSISWG text editor

2006-09-05T13:54:00.000+10:00

Some blog and wiki websites allow users to edit their blogs or wiki articles with various formatting options such as bold, italic and even allowing hyperlink image insertion. it looks like a lightweight "Word".

Here are such text editors I found on the web. They can be integreated into your web application or some online content management systems (CMS) so that users can output beautiful texts

FCKeditor - The text editor for Internet (open souce, LGPL(?))

And here's a long list:
Web Software Components: WYSIWYG Editors at htmlArea.com

Update FC3 to FC4 (or FC5) Using Yum

2006-07-13T15:22:00.000+10:00

The following article is quite helpful for those who want to upgrade Fedora core version3 to Fedora core version 4/5

Update FC3 to FC4 Using Yum | Rogue Wolves

mod_write: rewrite the urls and make them user/search engine friendly

2006-07-01T23:01:00.000+10:00

Here are topics describing how to use mod_write, one module of apache to rewrite the URLs, making them look pretty good and friendly for both human users and search engines.

Search Engine Friendly URLs with mod_rewrite
Using mod_rewrite with Apache and PHP

Change text mode to binary in CVS

2006-06-26T12:52:00.000+10:00

It's a common mistake to check in binary files in text mode in CVS.
There are commands to correct this:
cvs admin -kb thefile
cvs update -A thefile

Refer to the following for a script to do the job
CVS binary script

If you are working with newer version of CVSNT, you may probably need to use the following command instead:

$ cvs update -kb thefile
$ cvs commit -fm "Change substitution mode" thefile

More information can be found in CVSNT Manual.

create ISO image from CDROM/DVD in linux

2006-06-23T11:21:00.000+10:00

It's very simple. just use the following command:
dd if=/dev/hdc of=/home/username/cdcopy.iso

remember to umount the cd-rom before using the above command.

more information:
macosxhints.com - Create an exact duplicate of a CD from the command line
howto create iso from cdrom? [Archive] - The macosxhints Forums
Linux Command Directory: dd

LaTeX Editor - a GUI editor for latex file

2006-06-14T21:44:00.000+10:00

Please refer to the following link:
Some well known GUI editors for Latex editing on Windows

Force English environment linux to use Chinese input methods

2006-05-09T17:23:00.000+10:00

Force English environment linux to use Chinese input methods.
So you can type Chinese in English environment. Here's the article about this topic:

让英文Linux系统显示和输入中文