Simon Brown's Blog: Comparing webapp frameworks : Model 1 with JSTL

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«Comparing webapp frameworks : Model 1 with scriptlets | Main | Comparing webapp frameworks : Model 1 with JSP XML »

Comparing webapp frameworks : Model 1 with JSTL

Posted by simongbrown on January 10, 2006 at 09:05 AM | Comments (2)

It's been a while since the last blog entry, but let's continue our look at the webapp frameworks with another model 1 implementation, this time using the JavaServer Pages Standard Tag Library (JSTL).

In Comparing webapp frameworks : Model 1 with scriptlets we saw that model 1 applications typically have some boilerplate code at the top of the page to "set the scene" and the use of scriptlets means short pieces of Java code scattered throughout the page to control the presentation logic. As an alternative to this, we could use the JSTL.

Home page
Here's the home page, implemented using the JSTL.

<%@ page contentType="text/html;charset=UTF-8" %>
<%@ taglib uri="http://java.sun.com/jstl/core_rt" prefix="c" %>
<%@ taglib uri="http://java.sun.com/jstl/fmt_rt" prefix="fmt" %>

<jsp:useBean id="blogService" scope="request" class="domain.BlogService"/>
<c:set var="blog" value="${blogService.blog}" />

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
 "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">

  <head>
    <title>${blog.name}</title>
    <link rel="stylesheet" href="screen.css" type="text/css" />
  </head>

  <body>
    <div id="container">
      <h1>${blog.name}</h1>
      <h2>${blog.description}</h2>

      <c:forEach var="blogEntry" items="${blog.blogEntries}">
        <div class="blogEntry">
          <h3>${blogEntry.title}</h3>

          <c:choose>
            <c:when test="${not empty blogEntry.excerpt}">
              ${blogEntry.excerpt}
              <p>
              <a href="viewBlogEntry.jsp?id=${blogEntry.id}">Read more</a>
              </p>
            </c:when>
            <c:otherwise>
              ${blogEntry.body}
            </c:otherwise>
          </c:choose>

          <p>
          Posted on <fmt:formatDate value="${blogEntry.date}"
                      timeZone="${blog.timeZone}" type="both"
                      dateStyle="long" timeStyle="long" />
          </p>
        </div>
      </c:forEach>
    </div>
  </body>

</html>

As you can see, the boilerplate code at the top of the page to locate the Blog instance has been replaced with a simple JSTL tag and access to all properties on blog is performed using the JSP expression language ${...} construct, which is very succinct. In addition, the code that handles the presentation logic of iteration, conditional output and formatting has also been replaced by some JSTL tags. Line for line, this version is shorter and more readable than the previous one.

Blog entry detail page
The blog entry detail page also benefits from using the JSTL, although the scriptlet at the top of the page to locate the required blog entry is actually longer than before in order to make the objects available to the JSTL tags.

<%@ page import="domain.*" %>
<%@ page contentType="text/html;charset=UTF-8" %>
<%@ taglib uri="http://java.sun.com/jstl/core_rt" prefix="c" %>
<%@ taglib uri="http://java.sun.com/jstl/fmt_rt" prefix="fmt" %>

<%
  BlogService blogService = new BlogService();
  Blog blog = blogService.getBlog();
  request.setAttribute("blog", blog);

  BlogEntry blogEntry = blog.getBlogEntry(request.getParameter("id"));
  if (blogEntry == null) {
    response.sendError(HttpServletResponse.SC_NOT_FOUND);
    return;
  } else {
    request.setAttribute("blogEntry", blogEntry);
  }
%>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
 "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">

  <head>
    <title>${blogEntry.title} : ${blog.name}</title>
    <link rel="stylesheet" href="screen.css" type="text/css" />
  </head>

  <body>
    <div id="container">
      <h1>${blog.name}</h1>
      <h2>${blog.description}</h2>

      <div class="blogEntry">
        <h3>${blogEntry.title}</h3>

        ${blogEntry.body}

        <p>
        Posted on <fmt:formatDate value="${blogEntry.date}"
                    timeZone="${blog.timeZone}" type="both"
                    dateStyle="long" timeStyle="long" />
        </p>
      </div>
    </div>
  </body>

</html>

Summary
As this example shows, the JSTL can be used to considerably reduce the need for Java code but ultimately the overall design of a model 1 page is still the same. It's hard to get away from having a block of Java code at the top of the page where processing needs to happen before the page is rendered. A good example is the blog entry detail page that looks up a blog entry given a specific ID. Next time, we'll look at a slightly different way to write the pages.

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Comments

Comments are listed in date ascending order (oldest first) | Post Comment

It's hard to get away from having a block of Java code at the top of the page where processing needs to happen before the page is rendered.

Not really - you could create a tag to do it. Something like this:

public int doStartTag() {
// bla-bla-bla
if (blogEntry == null) {
response.sendError(HttpServletResponse.SC_NOT_FOUND);
return SKIP_PAGE;
} else {
request.setAttribute("blogEntry", blogEntry);
return EVAL_PAGE;
}

Posted by: felipeal on January 11, 2006 at 10:59 AM

Good point, although architecturally you still have a page centric design, which may or may not be a bad thing depending on your point of view.

Posted by: simongbrown on January 12, 2006 at 02:53 AM

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