Get the W3C Node instance associated with the XPath selection supplied : XPath « XML « Java Tutorial

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2. XML
3. XPath

/*
 Milyn - Copyright (C) 2006

 This library is free software; you can redistribute it and/or
 modify it under the terms of the GNU Lesser General Public
 License (version 2.1) as published by the Free Software 
 Foundation.

 This library is distributed in the hope that it will be useful,
 but WITHOUT ANY WARRANTY; without even the implied warranty of
 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  
 
 See the GNU Lesser General Public License for more details:    
 http://www.gnu.org/licenses/lgpl.txt
 */


import org.w3c.dom.Attr;
import org.w3c.dom.DOMException;
import org.w3c.dom.Document;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.EntityResolver;
import org.xml.sax.ErrorHandler;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.SAXParseException;


import javax.xml.XMLConstants;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.FactoryConfigurationError;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import javax.xml.transform.stream.StreamSource;
import javax.xml.validation.Schema;
import javax.xml.validation.SchemaFactory;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpressionException;
import javax.xml.xpath.XPathFactory;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.io.StringReader;
import java.io.StringWriter;
import java.io.Writer;

/**
 * XMl utility methods.
 *
 * @author Tom Fennelly
 */

public class XmlUtil {

    /**
     * Document validation types.
     */
    public static enum VALIDATION_TYPE {
        /**
         * No validation.
         */
        NONE,
        /**
         * DTD based validation.
         */
        DTD,
        /**
         * XSD based validation.
         */
        XSD,
    }
    private static String ELEMENT_NAME_FUNC = "/name()";

    private static XPathFactory xPathFactory = XPathFactory.newInstance();
    /**
     * Get the W3C Node instance associated with the XPath selection supplied.
     *
     * @param node  The document node to be searched.
     * @param xpath The XPath String to be used in the selection.
     * @return The W3C Node instance at the specified location in the document,
     *         or null.
     */
    public static Node getNode(Node node, String xpath) {
        NodeList nodeList = getNodeList(node, xpath);

        if (nodeList == null || nodeList.getLength() == 0) {
            return null;
        } else {
            return nodeList.item(0);
        }
    }
    /**
     * Get the W3C NodeList instance associated with the XPath selection
     * supplied.
     *
     * @param node  The document node to be searched.
     * @param xpath The XPath String to be used in the selection.
     * @return The W3C NodeList instance at the specified location in the
     *         document, or null.
     */
    public static NodeList getNodeList(Node node, String xpath) {
        if (node == null) {
            throw new IllegalArgumentException(
                    "null 'document' arg in method call.");
        } else if (xpath == null) {
            throw new IllegalArgumentException(
                    "null 'xpath' arg in method call.");
        }
        try {
            XPath xpathEvaluater = xPathFactory.newXPath();

            if (xpath.endsWith(ELEMENT_NAME_FUNC)) {
                return (NodeList) xpathEvaluater.evaluate(xpath.substring(0,
                        xpath.length() - ELEMENT_NAME_FUNC.length()), node,
                        XPathConstants.NODESET);
            } else {
                return (NodeList) xpathEvaluater.evaluate(xpath, node,
                        XPathConstants.NODESET);
            }
        } catch (XPathExpressionException e) {
            throw new IllegalArgumentException("bad 'xpath' expression ["
                    + xpath + "].");
        }
    }

}