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An implementation of the JSP Standard Tag Library (JSTL).
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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.xml;

import javax.servlet.jsp.PageContext;
import javax.servlet.jsp.tagext.Tag;
import javax.servlet.jsp.tagext.TagSupport;
import javax.xml.transform.TransformerException;

import org.apache.taglibs.standard.util.XmlUtil;
import org.apache.xpath.VariableStack;
import org.apache.xpath.XPathContext;
import org.apache.xpath.objects.XBoolean;
import org.apache.xpath.objects.XNodeSet;
import org.apache.xpath.objects.XNumber;
import org.apache.xpath.objects.XObject;
import org.apache.xpath.objects.XString;
import org.w3c.dom.NodeList;

/**
 */
public class XalanUtil {
    /**
     * Return the XPathContext to be used for evaluating expressions.
     *
     * If the child is nested withing a forEach tag its iteration context is used.
     * Otherwise, a new context is created based on an empty Document.
     *
     * @param child the tag whose context should be returned
     * @param pageContext the current page context
     * @return the XPath evaluation context
     */
    public static XPathContext getContext(Tag child, PageContext pageContext) {
        // if within a forEach tag, use its context
        ForEachTag forEachTag = (ForEachTag) TagSupport.findAncestorWithClass(child, ForEachTag.class);
        if (forEachTag != null) {
            return forEachTag.getContext();
        }

        // otherwise, create a new context referring to an empty document
        XPathContext context = new XPathContext(false);
        VariableStack variableStack = new JSTLVariableStack(pageContext);
        context.setVarStack(variableStack);
        int dtm = context.getDTMHandleFromNode(XmlUtil.newEmptyDocument());
        context.pushCurrentNodeAndExpression(dtm, dtm);
        return context;
    }

    /**
     * Return the Java value corresponding to an XPath result.
     *
     * @param xo the XPath type
     * @return the corresponding Java value per the JSTL mapping rules
     * @throws TransformerException if there was a problem converting the type
     */
    static Object coerceToJava(XObject xo) throws TransformerException {
        if (xo instanceof XBoolean) {
            return xo.bool();
        } else if (xo instanceof XNumber) {
            return xo.num();
        } else if (xo instanceof XString) {
            return xo.str();
        } else if (xo instanceof XNodeSet) {
            NodeList nodes = xo.nodelist();
            // if there is only one node in the nodeset return it rather than the list
            if (nodes.getLength() == 1) {
                return nodes.item(0);
            } else {
                return nodes;
            }
        } else {
            // unexpected result type
            throw new AssertionError();
        }
    }
}