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'rapiddweller Common' is an open source Java library forked from Databene Commons by Volker Bergmann. It provides extensions to the Java core library by utility classes, abstract concepts and concrete implementations.
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/*
 * Copyright (C) 2004-2015 Volker Bergmann ([email protected]).
 * All rights reserved.
 *
 * 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 com.rapiddweller.common.xml;

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

import javax.xml.namespace.QName;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpressionException;
import javax.xml.xpath.XPathFactory;
import java.util.List;

/**
 * Provides XPath query functionality on XML documents and elements.
 * Created: 28.03.2014 16:55:12
 *
 * @author Volker Bergmann
 * @since 0.5.29
 */
public class XPathUtil {

  /**
   * Query elements list.
   *
   * @param base       the base
   * @param expression the expression
   * @return the list
   * @throws XPathExpressionException the x path expression exception
   */
  public static List queryElements(Node base, String expression) throws XPathExpressionException {
    return XMLUtil.toElementList(queryNodes(base, expression));
  }

  /**
   * Query element element.
   *
   * @param base       the base
   * @param expression the expression
   * @return the element
   * @throws XPathExpressionException the x path expression exception
   */
  public static Element queryElement(Node base, String expression) throws XPathExpressionException {
    return (Element) query(base, expression, XPathConstants.NODE);
  }

  /**
   * Query element text string.
   *
   * @param base              the base
   * @param elementExpression the element expression
   * @return the string
   * @throws XPathExpressionException the x path expression exception
   */
  public static String queryElementText(Node base, String elementExpression) throws XPathExpressionException {
    // a direct string query for the content of a missing element would return an empty string,
    // not allowing to differ an empty element from a missing one, so I need to take a two-step approach:
    Element element = queryElement(base, elementExpression);
    if (element == null) {
      return null;
    }
    return element.getTextContent();
  }

  /**
   * Query attribute string.
   *
   * @param base              the base
   * @param elementExpression the element expression
   * @param attributeName     the attribute name
   * @return the string
   * @throws XPathExpressionException the x path expression exception
   */
  public static String queryAttribute(Node base, String elementExpression, String attributeName) throws XPathExpressionException {
    // since the result of a string query does not differentiate between empty ("") and not found (null), I need to apply a workaround
    // see http://stackoverflow.com/questions/17390684/jaxp-xpath-1-0-or-2-0-how-to-distinguish-empty-strings-from-non-existent-value
    Element element = queryElement(base, elementExpression);
    if (element == null) {
      return null;
    }
    NodeList nodes = queryNodes(element, "@" + attributeName);
    return (nodes.getLength() == 0 ? null : nodes.item(0).getTextContent());
  }

  /**
   * Query string string.
   *
   * @param base       the base
   * @param expression the expression
   * @return the string
   * @throws XPathExpressionException the x path expression exception
   */
  public static String queryString(Node base, String expression) throws XPathExpressionException {
    return (String) query(base, expression, XPathConstants.STRING);
  }

  /**
   * Query nodes node list.
   *
   * @param base       the base
   * @param expression the expression
   * @return the node list
   * @throws XPathExpressionException the x path expression exception
   */
  public static NodeList queryNodes(Node base, String expression) throws XPathExpressionException {
    return (NodeList) query(base, expression, XPathConstants.NODESET);
  }

  /**
   * Query node node.
   *
   * @param base       the base
   * @param expression the expression
   * @return the node
   * @throws XPathExpressionException the x path expression exception
   */
  public static Node queryNode(Node base, String expression) throws XPathExpressionException {
    return (Node) query(base, expression, XPathConstants.NODE);
  }

  /**
   * Query object.
   *
   * @param base       the base
   * @param expression the expression
   * @param returnType the return type
   * @return the object
   * @throws XPathExpressionException the x path expression exception
   */
  public static Object query(Node base, String expression, QName returnType) throws XPathExpressionException {
    XPath xpath = XPathFactory.newInstance().newXPath();
    return xpath.evaluate(expression, base, returnType);
  }

  /**
   * Is valid x path boolean.
   *
   * @param expression the expression
   * @return the boolean
   */
  public static boolean isValidXPath(String expression) {
    try {
      XPath xpath = XPathFactory.newInstance().newXPath();
      xpath.compile(expression);
      return true;
    } catch (XPathExpressionException e) {
      return false;
    }
  }

}