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"
"http://java.sun.com/j2ee/dtds/web-jsptaglibrary_1_1.dtd">
<taglib>
<tlibversion>1.0</tlibversion>
<jspversion>1.1</jspversion>
<shortname>oreillySamples</shortname>
<info>OReilly Sample Tag library</info>

<tag>
<name>hello</name>
<tagclass>com.ivy.tags.Hello </tagclass>

<bodycontent>JSP</bodycontent>
<info>
This is a simple hello tag.
</info>

<attribute>
<name>name</name>
<required>false</required>
<rtexpvalue>true</rtexpvalue>
</attribute>


<attribute>
<name>iterations</name>
<required>false</required>
<rtexpvalue>false</rtexpvalue>
</attribute>

</tag>
</taglib>

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>");
else
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
return EVAL_BODY_TAG;
}

//For the end part execution

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

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

3. JSP PAGE

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>
</sample:hello>

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.

Reference http://css-tricks.com/css-sprites-what-they-are-why-theyre-cool-and-how-to-use-them/

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.