Java(TM) Boutique - Introducing: the Struts bean and logic Tag Libraries

Tutorials : Introducing: the Struts bean and logic Tag Libraries :

Using tags or not - an example

Let's look at a situation where we must construct a jsp-page that contains a list of DVDs. Each DVD is represented by this bean, where we can store the title, length, and a list of actors:

package hansen.playground;

import java.util.*;

public class DVD {
  String title;
  int length;
  List actors;
  
  public DVD(String title, int length, List actors) {
    this.title = title;
    this.length = length;
    this.actors = actors;
  }
  
  public String getTitle() {return title;}
  
  public int getLength() {return length;}
  
  public List getActors() {
    return actors;
  }

}

- Figure 1: The DVD class

To hold the DVD collection we use a simple bean like this:

package hansen.playground;

import java.util.*;

public class DVDHandler {
  List DVDList = new LinkedList();
 
  public DVDHandler() {
    init();
  }
  
  public void init() {
    List list1 = new LinkedList();
    list1.add("Ian Holm");
    list1.add("Elijah Wood");
    list1.add("Ian McKellen");
    DVD dvd1 = new DVD("Lord of the Rings: 
	  The Fellowship of the Ring", 178, list1);
    DVDList.add(dvd1);
    
    List list2 = new LinkedList();
    list2.add("Keanu Reeves");
    list2.add("Laurence Fishburne");
    DVD dvd2 = new DVD("The Matrix", 136, list2);
    DVDList.add(dvd2);
  }  
  
  public List getDVDList() {
    return DVDList;
  }  

}

- Figure 2: The DVDHandler class

For the simplicity of the example the DVDHandler is initiated from its constructor to hold two DVDs.

The layout of the HTML page should be a simple table looking like this:

- Figure 3: HTML view of the DVDs

First we'll code this without any tags and only using Java code in scriplets. The algorithm is simple: loop through the DVDs in DVDHandler and show each of them in a table row:

<%@ page import="java.util.*" %>
<%@ page import="hansen.playground.*" %>

<jsp:useBean id="dvds" class="hansen.playground.DVDHandler" 
  scope="request"/>

<body>

<h2>DVD library</h2>
<table border=1 bgcolor="#FFFFCC">
  <tr>
    <th>Title</th>
    <th>Length (min.)</th>
    <th>Actors</th>
  </tr>  
<%
  List list = dvds.getDVDList();
  for (Iterator i = list.iterator(); i.hasNext();) {
    DVD dvd = (DVD)i.next();
%>
  <tr>
    <td><%=dvd.getTitle()%></td>
    <td><%=dvd.getLength()%></td>
    <td><%=dvd.getActors()%></td>
  </tr>
<%
  }
%>  
</table>

</body>

- Figure 4: A jsp-page with no tags

Comments to this solution:

the jsp:useBean directive will instantiate the DVDHandler and fill in the two DVDs
in order to get the title, length, and actors we must cast the element in list to the DVD class
we use 4 scriptlets in the page
26 non-blank lines of code

If we use Struts tags then we can code it in a much cleaner way:

<%@ taglib uri="/WEB-INF/struts-bean.tld"  prefix="bean" %>
<%@ taglib uri="/WEB-INF/struts-logic.tld" prefix="logic" %>

<jsp:useBean id="dvds" class="hansen.playground.DVDHandler" 
  scope="request"/>

<body>

<h2>DVD library</h2>
<table border=1 bgcolor="#FFFFCC">
  <tr>
    <th>Title</th>
    <th>Length (min.)</th>
    <th>Actors</th>
  </tr>  
<logic:iterate id="dvd" name="dvds" property="DVDList">
  <tr>
    <td><bean:write name="dvd" property="title" /></td>
    <td><bean:write name="dvd" property="length" /></td>
    <td><bean:write name="dvd" property="actors" /></td>
  </tr>
</logic:iterate>
</table>

</body>

- Figure 5: A jsp-page using tags

Comments to this solution:

no Java code!
two Struts tags used: iterate and write

no need to use the DVD class
20 non-blank lines of code

Not every case can be solved this elegantly using Struts tags, but I hope the example made you interested in learning more about the tags. So let's turn to the two libraries: bean and logic, to see how the tags herein often can help you build more readable and maintainable jsp pages.

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