Wednesday, September 24, 2008

Quartz - For Scheduling

Quartz is a full-featured, open source job scheduling system that can be integrated with,or used along side virtually any J2EE or J2SE application.It can mainly be used for Driving WrkFlow and System maintainance.
It can be integrated with any system with ease.It can perform simple or complicated schedules based on given cron expression.The execution logic can be embedded into simple java classes by implementing certain intefaces.
The job information can either be stored in memory through RAMJobStore or can be stored in relational databases using JDBCJobStore.If RAMJobStore is used whenever the server restarts, previously scheduled data is lost.
For scheduling jobs a scheduler needs to be started and jobs can be added as shown below.
SchedulerFactory schedFact = new org.quartz.impl.StdSchedulerFactory();
Scheduler sched = schedFact.getScheduler();
JobDetail jobDetail = new JobDetail("myJob", null, DumbJob.class);
Trigger trigger = TriggerUtils.makeHourlyTrigger(); // fire every hour trigger.setStartTime(TriggerUtils.getEvenHourDate(new Date())); // start on the next even hour trigger.setName("myTrigger");
sched.scheduleJob(jobDetail, trigger);
Custom job should implement the following interface
Job Interfacepackage org.quartz;
public interface Job {
public void execute(JobExecutionContext context) throws JobExecutionException; }
CronTrigger needs to be used for more complicated schedules.
An example of a complete cron-expression is the string "0 0 12 ? * WED" - which means "every Wednesday at 12:00 pm".

Thursday, September 11, 2008

Writing Simple Taglibs

Writing tag libraries has mainly 3 parts

1 .The tld file defining the tag parameters

2. Java Class Containing the implementation of the Tag

3. Jsp Code Calling the Taglib

1.Tld for Tag

<?xml version="1.0" encoding="ISO-8859-1" ?>
<!DOCTYPE taglib PUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag Library 1.1//EN"
<info>OReilly Sample Tag library</info>

<tagclass>com.ivy.tags.Hello </tagclass>

This is a simple hello tag.




2.Java Class For the Tag

public class Hello extends BodyTagSupport {
private String name=null;
private int iterations=1;

* Getter/Setter for the attribute name as defined in the tld file
* for this tag - Name & iterations

//core content of the tag needs to be written here

public int doStartTag() throws JspTagException{
try {
JspWriter out = pageContext.getOut();
out.println("<table border=\"1\">");
if (name != null)
out.println("<tr><td> Hello " + name + " </td></tr>");
out.println("<tr><td> Hello World <td></tr>");
} catch (Exception ex) {
throw new JspTagException("All is not well in the world." + ex );
// Evaluate the body if there is one

//For the end part execution

public int doEndTag() throws JspTagException {
try {
JspWriter out = pageContext.getOut();
} catch (Exception ex){
throw new JspTagException("All is not well in the world." + ex);

public int doAfterBody() throws JspTagException {
if (iterations >= 1) {
BodyContent body = getBodyContent();
try {
JspWriter out = body.getEnclosingWriter();
body.clearBody(); // Clear for next evaluation
} catch(IOException ioe) {
throw new JspTagException("Error in Hello tag doAfterBody " + ioe);
} else {


Include the written tld <%@ taglib uri="./sample.tld" prefix="sample" %>

<sample:hello name="userName" iterations="5">
<tr><td><b>Have a nice day</b></td></tr>

CSS Sprite - Another Web Optimisation Technique

When there are lots of images to be downloaded for a web page, the best option would be to use Css Sprite.In simple
words it reduces the number of images to be downloaded into one single big image.

Thus all the image requests will be reduced into one single request.At slight cost of increase in size better performance is attained.

Different Technique can be used to a create a single image from multiple images. The single image needs to be mentioned in the css and
where the individual images are required in the jsp the big image is specified with the offset, which cuts off the unwanted part of the image.


Multiple images before Sprite

#nav li a {background:none no-repeat left center}
#nav li a.item1 {background-image:url('../img/image1.gif')}
#nav li a:hover.item1 {background-image:url('../img/image1_over.gif')}
#nav li a.item2 {background-image:url('../img/image2.gif')

Sungle Image with Sprite & offsets mentioned for each image

#nav li a {background-image:url('../img/image_nav.gif')}
#nav li a.item1 {background-position:0px 0px}
#nav li a:hover.item1 {background-position:0px -72px}
#nav li a.item2 {background-position:0px -143px;}

The website provides interface which can take in images uploaded as zip and convert into a single image.

Free Domain Names @!