How to avoid using scriptlets in my JSP page?

Solution 1:

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>
  &nbsp;
</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>
  &nbsp;
</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.

Solution 2:

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/')

Solution 3:

Scriptlets aren't the worst thing in the world. An important consideration is to think about who is going to be maintaining the code. If its web designers who don't have much Java experience, you are probably better off going with tag libraries. However, if Java developers are doing the maintainance, it may be easier on them to go with scriptlets.

If you end up using a tag library and JSTL, you are expecting the maintainer to also learn the tag library and know JSTL. Some developers will be fine with this as it is a skill they want or already have, but for some developers who only have to deal with JSPs every few months or so, it can be lot less painful to work with clearly written scriptlets written in nice, familiar Java.

How to avoid using scriptlets in my JSP page?

Solution 1:

Solution 2:

Solution 3:

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