org.apache.taglibs.standard.tag.common.core.ChooseTag Maven / Gradle / Ivy
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/*
* Copyright (c) 1997-2020 Oracle and/or its affiliates. All rights reserved.
* Copyright 2004 The Apache Software Foundation
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.taglibs.standard.tag.common.core;
import jakarta.servlet.jsp.JspException;
import jakarta.servlet.jsp.tagext.TagSupport;
import org.apache.taglibs.standard.resources.Resources;
/**
* Tag handler for <choose> in JSTL.
*
* <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 true if the subtag should evaluate its condition
* and decide whether to run, false 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
}
}