A Brief Introduction to Struts – Expression Language
by Benoy Jose
Introduction:
Struts is a robust and powerful framework which promised
scalability, separation of concerns and reusability. The tag
libraries introduced in Struts made JSP pages more readable and
maintainable. However in the past my opinion was that this
neatness of the JSP page came at a price. A confusing tag
library structure and a learning curve that could deter a lot of
people. I would agree that once a person is comfortable with the
tags, writing JSP pages is simple but why would you want to make
a developer go through a learning process.
Ideally I would think of a scripting platform which is easy to
use, easily maintainable and one that can be learned easily. The
present tag libraries shipped with struts deviate from the
regular way JSP’s were written and introduce a new way of
writing code. This seemed counter productive as a vast number of
programmers would now need to learn some new concept of writing
JSP pages which could be used mostly with Struts. Another
argument in its favor is the ease it offers non-programmers to
write JSP code. Honestly though, I haven’t encountered many
instances where non-programmers, graphic artists and people with
absolutely no programming experience were writing JSP pages.
One thing these tags surely help is in streamlining regular and
mundane iteration tasks on a JSP page and makes them more
consistent and neat, but I still doubted if this should was
reason enough to include a complex and confusing tag library
into the Struts framework. My opinion surely changed when I saw
the Expression Language (EL) or JSTL.
Sample:
How many times have you written JSP code like the one below and
got confused with the names, ids and properties of a Struts
custom tag. Though the code looked elegant I personally found it
difficult to remember all those logic tags and iterate tags and
what they and their attributes did. The problem is compounded
when you have multiple collections embedded into a collection
which in turn is accessible to the page as a bean attribute.
<logic:iterate id="myColl" collection="<%= someColl %>">
Title = <bean:write name="SomeColl" property="title"/>
<logic:iterate id="SecColl" collection ="<%=secColl%>">
<logic:equal name="someName" property="someProp" value="whichValue">
Price =
</logic:equal>
</logic:iterate>
</logic:iterate>
Compare the above code with the one below written in JSTL.
<c:forEach var ="myColl" items="${someColl}">
<c:out value="Title is ${myColl.title}">
<c:forEach var="secColl" items="${secColl}">
<c:if test= "${myColl.name = secColl.name}">
<c:out value ="Oh they are the Same value">
<c:forEach>
</c:forEach>
So which looks easier to program and still looks as readable.
Well though the code above looks like Perl, python or some other
scripting language, it is actually not. It is a tag based
scripting language that has its roots borrowed from Perl. The
language makes it easy for developers who are used to embedding
JSP scriptlets in JSP pages. In the following sections I shall
describe a few important expression language tags that could be
useful in manipulating JSP pages. I will only be discussing the
tags and how they can be useful. Please refer to Sun’s website
http://java.sun.com/products/jsp/jstl/index.jsp for information
on installation and configuration of JSTL.
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