Reviews : Java Books :
JSP Tag Libraries : Chapter 10: Iterating with Tags

Listing 10. 6 Source code for the ForeachTag handler class

package book.iteration; 

import java.util.StringTokenizer; 
import java.util.LinkedList; 
import java.util.Iterator; 
import java.util.List; 
import book.util.LocalStrings; 
import book.util.ExBodyTagSupport; 
import javax.servlet.jsp.JspException; 

public class ForeachTag extends IterationTagSupport { 
	static LocalStrings ls = 
		LocalStrings.getLocalStrings(ForeachTag.class); 

	protected String elements = null; 

	public void setElements(String elements) 
	{ 
		this.elements = elements; 
	} 
	protected void fetchIterationSupport() 
		throws JspException 
	{ 
		List l = new LinkedList(); 
		StringTokenizer st = new StringTokenizer( elements, ","); 
		while( st.hasMoreTokens()) { 
			l. add( st.nextToken()); 
		} 
		elementsList = new IteratorIterationSupport( l.iterator()); 
	} 

protected void clearProperties() { elements = null; super.clearProperties(); } } class IteratorIterationSupport implements IterationSupport { Iterator i = null; IteratorIterationSupport(Iterator i) { this. i = i; } public boolean hasNext() throws JspException { return i.hasNext(); } public Object getNext() throws JspException { return i.next(); } }

Parsing the list specification string and making an IterationSupport out of it.

Clearing the additional tag property.

Implementing an IterationSupport class that uses a Java Iterator object.

The new ForeachTag has most of its code implementing its tag-specific functionality, that is, dealing with an Iterator of Strings. Also of note in our implementation is the additional IteratorIterationSupport class we created, which is simply an implementation of the generic IterationSupport that works on the java.util.Iterator interface. We can imagine a similar class that works on Arrays and even another for Enumerations (or perhaps one that handles all?). The IteratorIterationSupport class is not, of course, unique to ForeachTag and we will be able to reuse it many times in other specialized tags. We now have a way to easily create iteration tags that iterate on all sorts of objects. We'll flex the power of this infrastructure in the next section in creating a tag that is capable of iterating on just about anything.

How to Add Java Applets to Your Site

New on the Java Boutique:

New Review:

Time Management Made Easy with the Quartz Enterprise Job Scheduler
Why not just use the Java timer API? This open source scheduling API boasts simplicity, ease-of-integration, a well-rounded feature set, and it's free!

New Applet:

Reverse Complement
Reverse Complement is a simple applet that converts DNA or RNA sequences into three useful formats.

Elsewhere on internet.com:

WebDeveloper Java
Lots of Java information on webdeveloper.com

WDVL Java
Thorough Java resource at the Web Developer's Virtual Library.

ScriptSearch Java
Hundreds of free Java code files to download.

jGuru: Your View of the Java Universe
Customizable portal with online training, FAQs, regular news updates, and tutorials.