How to avoid using scriptlets in my JSP page?
I've been told that the use of scriptlets (<%= ... %>) in my JSP pages isn't such a great idea.
Can someone with a bit more java/jsp experience please give me some pointers as to how to change this code so its more 'best practice', whatever that may be?
This JSP is actually my sitemesh main decorator page. Basically my web design has a tab strip and a submenu, and i wish to somehow highlight the current tab and show the correct submenu by looking at the current request URI.
<%@ taglib uri="http://www.opensymphony.com/sitemesh/decorator" prefix="decorator" %>
<html>
<head>
<title>My Events - <decorator:title /></title>
<link href="<%= request.getContextPath() %>/assets/styles.css" rel="stylesheet" type="text/css" />
</head>
<body>
<div class="tabs">
<a
<%= request.getRequestURI().contains("/events/") ? "class='selected'" : "" %>
href='<%= request.getContextPath() %>/events/Listing.action'>Events</a>
<a
<%= request.getRequestURI().contains("/people/") ? "class='selected'" : "" %>
href='<%= request.getContextPath() %>/people/Listing.action'>People</a>
</div>
<div class="submenu">
<% if(request.getRequestURI().contains("/events/")) { %>
<a href="Listing.action">List of Events</a>
|<a href="New.action">New Event</a>
<% } %>
<% if(request.getRequestURI().contains("/people/")) { %>
<a href="Listing.action">List of People</a>
|<a href="New.action">New Person</a>
<% } %>
</div>
<div class="body">
<decorator:body />
</div>
</body>
</html>
Thanks all
I think it helps more if you see with your own eyes that it can actually be done entirely without scriptlets.
Here's a 1 on 1 rewrite with help of among others JSTL (just drop jstl-1.2.jar in /WEB-INF/lib ) core and functions taglib:
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ taglib uri="http://java.sun.com/jsp/jstl/functions" prefix="fn" %>
<html>
<head>
<title>My Events - <decorator:title /></title>
<link href="${pageContext.request.contextPath}/assets/styles.css" rel="stylesheet" type="text/css" />
</head>
<body>
<div class="tabs">
<a
${fn:contains(pageContext.request.requestURI, '/events/') ? 'class="selected"' : ''}
href="${pageContext.request.contextPath}/events/Listing.action">Events</a>
<a
${fn:contains(pageContext.request.requestURI, '/people/') ? 'class="selected"' : ''}
href="${pageContext.request.contextPath}/people/Listing.action">People</a>
</div>
<div class="submenu">
<c:if test="${fn:contains(pageContext.request.requestURI, '/events/')}">
<a href="Listing.action">List of Events</a>
|<a href="New.action">New Event</a>
</c:if>
<c:if test="${fn:contains(pageContext.request.requestURI, '/people/')}">
<a href="Listing.action">List of People</a>
|<a href="New.action">New Person</a>
</c:if>
</div>
Here's a more optimized rewrite, note that I used c:set to "cache" expression results for reuse and that I use HTML <base> tag to avoid putting the context path in every link (just make all relative URL's in your webpage relative to it --without the leading slash!):
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ taglib uri="http://java.sun.com/jsp/jstl/functions" prefix="fn" %>
<c:set var="isEvents" value="${fn:contains(pageContext.request.requestURI, '/events/')}" />
<c:set var="isPeople" value="${fn:contains(pageContext.request.requestURI, '/people/')}" />
<html>
<head>
<title>My Events - <decorator:title /></title>
<base href="${pageContext.request.contextPath}">
<link href="assets/styles.css" rel="stylesheet" type="text/css" />
</head>
<body>
<div class="tabs">
<a ${isEvents ? 'class="selected"' : ''} href="events/Listing.action">Events</a>
<a ${isPeople ? 'class="selected"' : ''} href="people/Listing.action">People</a>
</div>
<div class="submenu">
<c:if test="${isEvents}">
<a href="Listing.action">List of Events</a>|<a href="New.action">New Event</a>
</c:if>
<c:if test="${isPeople}">
<a href="Listing.action">List of People</a>|<a href="New.action">New Person</a>
</c:if>
</div>
It can actually be optimized more if you collect all those "hardcoded" values like events and people and link texts in a Map in the application scope and use under each the JSTL <c:forEach> to display the tabs.
As to your actual question, you can disable scriptlets (and get runtime errors about using it) by adding the following entry in webapp's web.xml . It may help to spot overseen scriptlets.
<jsp-config>
<jsp-property-group>
<url-pattern>*.jsp</url-pattern>
<scripting-invalid>true</scripting-invalid>
</jsp-property-group>
</jsp-config>
To learn more about EL, check the Java EE tutorial part II chapter 5. Implicit EL objects, such as ${pageContext} are described here. To learn more about JSTL, check the Java EE tutorial part II chapter 7. Note that JSTL and EL are two separate things. JSTL is a standard taglib and EL just enables to access backend data programmatically. Although it is normally used in taglibs like JSTL, it can also be used standalone in template text.
As an aside, is <%= request.getContextPath() %> an acceptable use of scriptlets that isn't frowned on so much?
This may be an unpopular opinion, but if all you do are simple conditionals and text insertions, I cannot find much fault in the use of scriptlets. (Note the if)
I'd probably use JSTL and the expression language, but mostly because it can be less typing, and IDE support may be better (but a good JSP IDE can also find missing closing brackets and stuff like that).
But fundamentally (as in "keep logic out of templates") I fail to see any difference between
<% if(request.getRequestURI().contains("/events/")) { %>
and
${fn:contains(pageContext.request.requestURI, '/events/')
This isn't a direct answer to your question (and there are already several good ones, so I won't try to add to it), but you did mention:
Can someone with a bit more java/jsp experience please give me some pointers as to how to change this code so its more 'best practice', whatever that may be?
In my opinion, best practice, with regards to JSP, is that it should be used strictly as a templating engine, and no more (ie, no business logic in there). Using JSTL, as many pointed out, definitely helps you get there, but even with JSTL, it's easy to do to much in a JSP.
I personally like to follow the rules laid out in Enforcing Strict Model-View Separation in Templating Engines by the Terence Parr when developing in JSP. The paper mentions the purpose of templating engines (separating model and view), and characteristics of a good templating engine. It takes a good look at JSP and points out ways it's not a good templating engine. Not surprisingly, JSP is basically too powerful and allows developers to do too much. I strongly recommend reading this paper, and it'll help you restrict yourself to the "good" parts of JSP.
If you read only one section in that paper, read chapter 7, which includes the following rules:
Incidentally, Terence has created his own templating engine called String Template which supposedly does a really good job of enforcing these rules. I have no personal experience with it, but would love to check it out on my next project.
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