An Introduction to JSTL

AsJ2EE programmers, we are familiar with Servlets , JSPand JavaBeans.Any JSP page should encapsulate the business
logic in a bean and invoke it by using <jsp:useBean>tag.Till recently, a combination of Servlets, JSP and beans was the
standard practice. But, the JCP realeased an API for
enabling programmers to create custom tags and use them in their JSP pages. The
difference between javabean and java custom tags was
that, though both made use of java classes,tags can be used by non-programmers
also withoutknowledge of Java
programming, just as they would use html tags.( From a programmer's perspective,however, a much more important distinction is that
tags are specific to the page in which they are created while javabeans are general. )

{{{Back in 1998, a
Web-Server Technology , known as ColdFusion ,
created by Allaire of Allaire
Corporation, was very much in demand!. It was a purely tag-based language,
using which page-authors can turn into programmers overnight. The tags were so
powerful and simple to use! There is a separate lesson on using ColdFusion for typical web-based database opeartions, elsewhere in this edition, just to indicate the
source of inspiration of the tag library idea, of the JSTL. To this day, ColdFusion is unbeatable, in its power,speed, ease of use and productivity. However, among
the various web-server technologies ( namely ASP, Servlets,
JSP,Perl,PHP , ColdFusion
& ASP.net), CF is the only technology that is not free!And
perhaps for this reason, it is no longer popular in Indian environment, though
it is said to be very much in vogue still, in US!

MacroMedia of 'Flash fame' purchased ColdFusion .There was even a tutorial on MacroMediaColdFusionExprsess in DeveloperIQ., a few
months back.It is interesting to make a comparison of
the CF tags approach and the JSTL approach., especially ,
in DataBaseoperations.Readers
are requested to read the lesson on ColdFusion,in
this edition, after covering sql tags in JSTL , in
the fourth part of this tutorial..}}}

To resume,the release of the TagLibrary
API, triggereda lot ofactivity and hundreds of tags were
introduced by the java community, some of them 'open' and a few
'proprietary'.This led to a lot of
confusion in code maintenance, because knowledge of Java was no longer
sufficient to understand and interpret a given jsp
page using non-standard tags .The JCP had unwittinglyintroduced elements of confusion by the
JSP-Custom-Tag specification.

To correct this
problem, Sun and JCP, initiatedthe JSP-Standard
Tag Library (JSTL) project.Though there are a number of popular and powerful tag-libraries, it is
always better for j2ee coders toadopt the JCP standard because, it is
likely to be merged into the core specification of Java langauage
itself , in future. (That yardstick may be valid for all creations, in Java
world. Splintering of the Java platform due to' hyper-active creativity'without the corresponding discipline
to get it through a standards body ,is the greatest threat, looming large in
the Java-horizon.

Too
frequent revisions and additions, that too without caring for backward compatibility,are not conducive to
programmer productivityand the net
result is that programmers spend ,in learning new twists in grammar,theirprecious timewhich should have
been spent more usefully in applying that grammar in solving business-logic
problems and acquiring proficiency in the chosen application-domain. While, tag
library is sometimes very elegant and simple to use, it defeats the very
purpose if the tagsare not standard tags and if there is proliferation of
non-standard tags.It is for this
reason that JSTL merits our serious study and adoption.

JSTL is a quite recentdevelopment. It was only in 2003, that
the official version 1.1 was released and now incorporated intoJSP-2.

According to the latest position, the
JCP is suggesting that a JSP page should be completely free from any trace of
Java code!So, programmers who were
writing their JSP using Javabeans and scriptlets , may not be able to carry on in their old style
as,to prevent programmers from
introducing scripting sections in their pages, there is aprovisionfor turning off scriptlets altogether from a jsp page. If that happens ,all our
knowledge of Java coding will be of little use in creating a jsp page, though such knowledge may be useful in creating
beans and other types of java programs.

It is thus very important forJ2EE students, to
understand the trend and get to know the techniques, advantages and limitations
oftag libraries…In a way, a study of
JSTL is almost synonymouswith a study
of the latest version of JSP (ie) JSP2.0 .

—————————————

Without an introductory demo for each of
these types, it may be difficult to appreciate the significance of the above
lines. So we will now give simplest illustration.

[It
is presumed that readers are conversant with basic Servlets
& JSP techniques and executing them in Tomcat environment. In case of any
difficulty, they can refer to back issues of this magazine (
from Oct-2003onwards) and gain
access to a number of lessons for illustrations.]

Servlets are
full-fledged java-classes and so are very powerful. But, when we want to create
a dynamically-generated web-page using servlets, it
becomes difficult and clumsy. Let us consider a very simple example.

The
user fills up text in html form with his name and submits the form,to the servlet.
The servlet reads the data ,
appends a greeting and sends it back to the user.

———————————————–

We begin with a simple html form;

//greeting.htm

============================================

<html><body>

<formmethod=post

action=

'http://localhost:8080/servlet/greeting'>

<inputtype=textname='text1'>

<inputtype=submit>

</form>

</body>

</html>

——————————————-

(relevant section of
greeting.javaservlet)

//greeting.java
( code-snippet only)

public
void doPost(HttpServletRequestreq,

HttpServletResponseresp)

throwsServletException,IOException

{

resp.setContentType("text/html");

PrintWriterout
= resp.getWriter();

//——————————-

Strings
= req.getParameter("text1");

out.println("<html><bodybgcolor=yellow>");

out.println("wewelcome"+",<br>");

out.println (s);

out.println("</body> </html>");

}

———————————————–

It
will be noticed thatwe have to write so many 'out.println'
statements. This makes the page unreadable.( If
String-buffer is used , we can do it with just a single out.println
, butforming the correct string may
pose difficulties).

It is to solve this problemthat JSP was developed five years back(1999).While a servletinterposes HTMLin java code, JSP interposes java-code in
HTML, as some authors correctly observe..( in this
case, we have to modify the action field in html form, so that it refers to the
followinggreeting1.jsp).

Student
readers will know about 'delimiters'( <%).in
ASP. This is the same as inJSP. Only the syntax is slightly different.In
JSP parlance, the code within delimiters is known as 'scriptlet'.( see greeting1.jsp)

———————————————–

//greeting1.jsp

==========

<html>

<bodybgcolor=yellow>

<%

Strings = request.getParameter("text1");

out.println("we welcome"+<br>);

out.println(s);

%>

</body>

</html>

———————————————–

Some coders prefer to use expressions.

What
is an 'expression'? It is a method of sustituting
request-time values in html page. ( see
greeting2.jsp). Carefully note that there is no semi-colon after
("text1").

———————————————–

// greeting2.jsp

<html>

<bodybgcolor=yellow>

wewelcome <br>

<%=request.getParameter("text1")
%>

</body>

</html>

———————————————–

The
third variant is to use a javabean to encapsulate the
business-logic. Wedevelop a jsp-bean as follows:

——————————————

//greeter.java

packageourbeans;

public class greeter

{

public
greeter(){}

publicStringgreetme(Strings)

{

return"we welcome…"+s;

}

}

——————————————-

This
source file is compiled and the class-file is copied to :

'e:tomcat5webappsrootWEB-INFclassesourbeans'

(Carefully
note that WEB-INF folder name should be in capital letters).

—–

( Anytime, a new class is placed in
Tomcat, we should remember to restart the server).

We
can nowwrite our JSP code as follows:

————————————————

//
greeting3.jsp

<html>

<body>

<jsp:useBeanid='bean1'class='ourbeans.greeter'>

<%

Strings
= request.getParameter ("text1");

Stringr =bean1.greeteme(s);

out.println(r);

%>

</body>

We are now enteringJSTLzone.

How exactly we should proceed toinstalJSTL, we will take up shortly. For the
moment, we are just getting familiar with the required syntax.We begin withtaglib
directive.

<%@taglibprefix="c"uri="http://java.sun.com/jstl/core"%>

<c:setvar="a"value="sam"
/>

<c:outvalue="${a}"/>

———————————–

The
Dollar sign&
brace will be familiar ground for Perl
programmers.In JSTL & JSP-2, it isknown as EL (
Expression Language).

==============================================

To
consider another example,Inservlet & jsp,
we write:

String s = request.getParameter("text1");

to collect the input from the user.

——

The same job is done inJSTLby:

<c:setvar="s"
value="${param.text1}" >

==================================

With these brief hints, it should not be
difficult to understand the

followingJSPpage writtenbyusing JSTL core-tags.

———————————————–

//greeting4.jsp(usesJSTL)

===========

<%@taglibprefix="c" uri="http://java.sun.com/jstl/core"%>

<html>

<body>

<c:setvar=svalue="${param.text1}"
/>

We
welcome<br>

<c utvalue="${s}" />

</body>

</html>

———————————————–

In
the previousexamples,
there was java code in a few lines atleast. But, in theJSTLexample, we find that
there are only tags and no javascriptlets. This is the avowed objective
of the JSTLinitiative,

under the auspices of Java Community
Project! Why?This enables
, clean separation ofPage
author's role and Logic programmers' role. Thus maintenance becomes easy.

===============================================

There are five groups under which the JSTL
tags have been organized.

They are as follows:

1)core

2)xml

3)sql

4)formatting

5)functions.

———————————————–

The most difficult part isto set up Tomcatso that it executes JSTL.There are some basic requirements, before we
can experiment and study the use of JSTL.All that we
have studied in using Tomcat for servlets and JSP may
not be sufficient to learn JSTL, because, jstl
library is not built into Tomcat5even,
as yet.

Without hands-on experimention,
JSTL could be confusing and strange, because of thefact that it is veryrecent. But in coming months, support will be built into Tomcat and we won't
have to worry about installing the JSTLlibraries inside Tomcat. But, as it
is, we have to learn how to set up the necessary development environment..

So , how
do we go about , placing the JSTL libraries in tomcat?

————————————————

The best solution is to get JWSDP1.3.

This is Java Web Service Development'
Pack.

( Carefully note the version ,
however!).

It is good to start with this because, it
contains a lot of valuable software , including the
latest and greatest fromJCP, (ie) JSF

(Java
Server Faces)…. which may soon replace Struts.

We unzipthe jwsdp1.3and installit in C: drive.

Therearea number of
folders like JAXP, JAXR, JAXB,JAX-RPC,

JSF,
JSTL etc. in the JWSDP pack.

For the present, we are interested in JSTL
folder only. If we expand the JSTL folder, we findfoursub folders :

a)docs

b)lib

c)samples

d)tld(tag library descriptors)

————–

When we look into the 'lib' folder,
we findtwo jar files:

a)standard.jar

b)jstl.jar

———————————————–

We should copythese two jar files into:

'e:tomcat5webappsrootWEB-INFlib'

———————————————–

(
Remember to restart the Tomcat server).

That is
all that is required to useJSTL. !

The included
taglibrary descriptors do not have to be placed in
the WEB-INF folder.These files are alreadyincluded in the /META-INF folder of
the jstl.jar and so will be automatically

loaded by
Tomcat, when it is restarted.

***********************************************

( we are using
tomcat5 & jdk1.4.2)

( the results are
notensuredfor other environments.).( however, we adopted the same method in Tomcat4.1
with jdk1.41 and got correct functioning.)

===============================================

The JSTLfolder contains a sub-folder named 'tld'.There will be a number of tld
files there such as

c.tld,( core)

x.tld,(xml)

fmt.tld<span style="font-family: "