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package org.apache.taglibs.standard.tag.common.core;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.TagSupport;
import org.apache.taglibs.standard.resources.Resources;
/**
* <p>Tag handler for <choose> in JSTL.</p>
*
* <p><choose> is a very simple tag that acts primarily as a container;
* it always includes its body and allows exactly one of its child
* <when> tags to run. Since this tag handler doesn't have any
* attributes, it is common.core to both the rtexprvalue and expression-
* evaluating versions of the JSTL library.
*
* @author Shawn Bayern
*/
public class ChooseTag extends TagSupport {
//*********************************************************************
// Constructor and lifecycle management
// initialize inherited and local state
public ChooseTag() {
super();
init();
}
// Releases any resources we may have (or inherit)
public void release() {
super.release();
init();
}
//*********************************************************************
// Private state
private boolean subtagGateClosed; // has one subtag already executed?
//*********************************************************************
// Public methods implementing exclusivity checks
/**
* Returns status indicating whether a subtag should run or not.
*
* @return <tt>true</tt> if the subtag should evaluate its condition
* and decide whether to run, <tt>false</tt> otherwise.
*/
public synchronized boolean gainPermission() {
return (!subtagGateClosed);
}
/**
* Called by a subtag to indicate that it plans to evaluate its
* body.
*/
public synchronized void subtagSucceeded() {
if (subtagGateClosed)
throw new IllegalStateException(
Resources.getMessage("CHOOSE_EXCLUSIVITY"));
subtagGateClosed = true;
}
//*********************************************************************
// Tag logic
// always include body
public int doStartTag() throws JspException {
subtagGateClosed = false; // when we start, no children have run
return EVAL_BODY_INCLUDE;
}
//*********************************************************************
// Private utility methods
private void init() {
subtagGateClosed = false; // reset flag
}
}
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