Tutorials : A Brief Introduction to Struts – Expression Language :

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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