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JSP Tag Libraries : Chapter 10: Iterating with Tags

IterateTagExtraInfo

Accompanying the IterateTag is the IterateTagExtraInfo whose implementation is fairly effortless. Once again, we need to create this TagExtraInfo object for our IterateTag because we will be exporting a scripting variable from it. From an attribute and variable exportation point of view, IterateTag and ExportTag (as presented in chapter 8) are quite similar. The only difference is that our current variable is exported as a NESTED variable, meaning its scope only exists within the tag's body. Because they are so similar, all we need to do is inherit ExportTagExtraInfo (again, from chapter 8) and modify the VariableInfo it returns to reflect a NESTED variable. As listing 10. 10 shows, this is exactly what we did.

Listing 10. 10 Source code for the IterateTagExtraInfo class

package book.iteration; 

import book.reflection.ExportTagExtraInfo; 
import javax.servlet.jsp.tagext.TagData; 
import javax.servlet.jsp.tagext.TagExtraInfo; 
import javax.servlet.jsp.tagext.VariableInfo; 

public class IterateTagExtraInfo extends ExportTagExtraInfo { 
	public VariableInfo[] getVariableInfo(TagData data) 
	{ 
		VariableInfo[] rc = new VariableInfo[ 1]; 
		
		rc[0] = new VariableInfo(data.getId(), 
			guessVariableType( data), 
			true, 
			VariableInfo.NESTED);  
		return rc; 
	} 
} 

Returns a NESTED variable.

IterateTag's TLD

The last step in our implementation of IterateTag is its tag library descriptor entry as seen in listing 10.11.

Listing 10. 11 Tag library descriptor entry for IterateTag

<tag> 
	<name> iterate</name> 
	<tagclass> book.iteration.IterateTag</tagclass> 
	<teiclass> book.iteration.IterateTagExtraInfo</teiclass> 
	<bodycontent> JSP</bodycontent> 
	<info> 
		Iterate over an Object. The object can be an array, 
		Iterator or Enumeration. 
	</info> 
	
	<attribute> 
		<name> id</name> 
		<required> true</required> 
		<rtexprvalue> false</rtexprvalue> 
	</attribute> 
	<attribute> 
		<name> type</name> 
		<required> false</required> 
		<rtexprvalue> false</rtexprvalue> 
	</attribute> 
	<attribute> 
		<name> object</name> 
		<required> false</required> 
		<rtexprvalue> true</rtexprvalue> 
	</attribute> 
	<attribute> 
		<name> name</name> 
		<required> false</required> 
		<rtexprvalue> false</rtexprvalue> 
	</attribute> 
	<attribute> 
		<name> scope</name> 
		<required> false</required> 
		<rtexprvalue> false</rtexprvalue> 
	</attribute> 
	<attribute> 
		<name> index</name> 
		<required> false</required> 
		<rtexprvalue> true</rtexprvalue> 
	</attribute> 
	<attribute> 
		<name> property</name> 
		<required> false</required> 
		<rtexprvalue> false</rtexprvalue> 
	</attribute> 
</tag> 

The tag library entry is almost identical to the one we had for ExportTag. The only significant difference is that ExportTag had an empty body, whereas IterateTag has, of course, a JSP body.

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