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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