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Title: JSP Tag Libraries

ISBN: 193011009X

US Price: $35.96

Publication Date: May 2001

Pages: 656

© 2001 Manning Publications Co.

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

SimpleForeachTag's TagExtraInfo

Following the development of SimpleForeachTag we must now create its TagExtraInfo counterpart. You may recall from our discussions of the TagExtraInfo class in chapters 6 and 8, we need to create a subclass of TagExtraInfo whenever we have a tag that exports a scripting variable. Since SimpleForeachTag will need to export the values of the iterator, we'll create a TagExtraInfo class for it that will inform the runtime of this. We'll call this class ForeachTagExtraInfo. Its implementation is in listing 10. 2 wherein you see that it merely notifies the JSP runtime that a new scripting variable of type String is exported.

Listing 10. 2 Source code for the ForeachTagExtraInfo class

package book.iteration; 

import javax.servlet.jsp.tagext.TagData; 
import javax.servlet.jsp.tagext.TagExtraInfo; 
import javax.servlet.jsp.tagext.VariableInfo; 

public class ForeachTagExtraInfo extends TagExtraInfo { 
	public VariableInfo[] getVariableInfo(TagData data) 
	{ 
		VariableInfo[] rc = new VariableInfo[1]; 
		rc[ 0] = new VariableInfo( data.getId(), 
			"java.lang.String", 
			true, 
			VariableInfo.NESTED); 
		return rc; 
	} 
}

NOTE Note that the scope defined for the scripting variable is NESTED, meaning the variable exists and is accessible only within the body of the tag that ex-ported it. This is important since the variable we export is our iterator, and so should exist only within the body of the loop.

SimpleForeachTag in action

Having written SimpleForeachTag and its TagExtraInfo we can now write JSP code to work with it. Since this is only the beginning of our iteration tags discussion, we will take that same JSP fragment and make it the content of our JSP as seen in listing 10.3.

Listing 10.3 JSP driver for SimpleForeachTag

<%@ page errorPage="error.jsp" %> 
<%@ taglib 
	uri="http://www.manning.com/jsptagsbook/iteration-taglib" 
	prefix="iter" %> 

<html> 
<body> 

<iter:foreach id="item" 
		elements="1,2,3,4"> 
The selected item is <%= item %> <br> 
</iter:foreach> 

</ body> 
</ html>

Now when we execute our JSP, SimpleForeachTag will repeat its body four times (one for each string in "elements"); first with 1 as the value of the item (our iterator), and lastly with 4 as its value.

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