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Apache XML Security for Java supports XML-Signature Syntax and Processing, W3C Recommendation 12 February 2002, and XML Encryption Syntax and Processing, W3C Recommendation 10 December 2002. As of version 1.4, the library supports the standard Java API JSR-105: XML Digital Signature APIs.

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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.xml.security.utils;

import javax.xml.XMLConstants;
import javax.xml.transform.TransformerException;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpression;
import javax.xml.xpath.XPathExpressionException;
import javax.xml.xpath.XPathFactory;
import javax.xml.xpath.XPathFactoryConfigurationException;

import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

/**
 * An implementation for XPath evaluation that uses the JDK API.
 */
class JDKXPathAPI implements XPathAPI {

    private XPathFactory xpf;

    private String xpathStr;

    private XPathExpression xpathExpression;

    /**
     *  Use an XPath string to select a nodelist.
     *  XPath namespace prefixes are resolved from the namespaceNode.
     *
     *  @param contextNode The node to start searching from.
     *  @param xpathnode
     *  @param str
     *  @param namespaceNode The node from which prefixes in the XPath will be resolved to namespaces.
     *  @return A NodeIterator, should never be null.
     *
     * @throws TransformerException
     */
    @Override
    public NodeList selectNodeList(
        Node contextNode, Node xpathnode, String str, Node namespaceNode
    ) throws TransformerException {
        if (!str.equals(xpathStr) || xpathExpression == null) {
            if (xpf == null) {
                xpf = XPathFactory.newInstance();
                try {
                    xpf.setFeature(XMLConstants.FEATURE_SECURE_PROCESSING, Boolean.TRUE);
                } catch (XPathFactoryConfigurationException ex) {
                    throw new TransformerException(ex);
                }
            }
            XPath xpath = xpf.newXPath();
            xpath.setNamespaceContext(new DOMNamespaceContext(namespaceNode));
            xpathStr = str;
            try {
                xpathExpression = xpath.compile(xpathStr);
            } catch (XPathExpressionException ex) {
                throw new TransformerException(ex);
            }
        }
        try {
            return (NodeList)xpathExpression.evaluate(contextNode, XPathConstants.NODESET);
        } catch (XPathExpressionException ex) {
            throw new TransformerException(ex);
        }
    }

    /**
     * Evaluate an XPath string and return true if the output is to be included or not.
     *  @param contextNode The node to start searching from.
     *  @param xpathnode The XPath node
     *  @param str The XPath expression
     *  @param namespaceNode The node from which prefixes in the XPath will be resolved to namespaces.
     */
    @Override
    public boolean evaluate(Node contextNode, Node xpathnode, String str, Node namespaceNode)
        throws TransformerException {
        if (!str.equals(xpathStr) || xpathExpression == null) {
            if (xpf == null) {
                xpf = XPathFactory.newInstance();
                try {
                    xpf.setFeature(XMLConstants.FEATURE_SECURE_PROCESSING, Boolean.TRUE);
                } catch (XPathFactoryConfigurationException ex) {
                    throw new TransformerException(ex);
                }
            }
            XPath xpath = xpf.newXPath();
            xpath.setNamespaceContext(new DOMNamespaceContext(namespaceNode));
            xpathStr = str;
            try {
                xpathExpression = xpath.compile(xpathStr);
            } catch (XPathExpressionException ex) {
                throw new TransformerException(ex);
            }
        }
        try {
            return (Boolean)xpathExpression.evaluate(contextNode, XPathConstants.BOOLEAN);
        } catch (XPathExpressionException ex) {
            throw new TransformerException(ex);
        }
    }

    /**
     * Clear any context information from this object
     */
    @Override
    public void clear() {
        xpathStr = null;
        xpathExpression = null;
        xpf = null;
    }

}