code: /*
   * 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.
   */
  /*
   * $Id$
   */
  package org.apache.xpath;
  
  import javax.xml.transform.TransformerException;
  
  import org.apache.xml.utils.PrefixResolver;
  import org.apache.xml.utils.PrefixResolverDefault;
  import org.apache.xpath.objects.XObject;
  
  import org.w3c.dom.Document;
  import org.w3c.dom.Node;
  import org.w3c.dom.NodeList;
  import org.w3c.dom.traversal.NodeIterator;
  
  /**
   * The methods in this class are convenience methods into the
   * low-level XPath API.
   * These functions tend to be a little slow, since a number of objects must be
   * created for each evaluation.  A faster way is to precompile the
   * XPaths using the low-level API, and then just use the XPaths
   * over and over.
   *
   * NOTE: In particular, each call to this method will create a new
   * XPathContext, a new DTMManager... and thus a new DTM. That's very
   * safe, since it guarantees that you're always processing against a
   * fully up-to-date view of your document. But it's also portentially
   * very expensive, since you're rebuilding the DTM every time. You should
   * consider using an instance of CachedXPathAPI rather than these static
   * methods.
   *
   * @see <a href="http://www.w3.org/TR/xpath">XPath Specification</a> 
   * */
  public class XPathAPI
  {
  
    /**
     * Use an XPath string to select a single node. XPath namespace
     * prefixes are resolved from the context node, which may not
     * be what you want (see the next method).
     *
     * @param contextNode The node to start searching from.
     * @param str A valid XPath string.
     * @return The first node found that matches the XPath, or null.
     *
     * @throws TransformerException
     */
    public static Node selectSingleNode(Node contextNode, String str)
            throws TransformerException
    {
      return selectSingleNode(contextNode, str, contextNode);
    }
  
    /**
     * Use an XPath string to select a single node.
     * XPath namespace prefixes are resolved from the namespaceNode.
     *
     * @param contextNode The node to start searching from.
     * @param str A valid XPath string.
     * @param namespaceNode The node from which prefixes in the XPath will be resolved to namespaces.
     * @return The first node found that matches the XPath, or null.
     *
     * @throws TransformerException
     */
    public static Node selectSingleNode(
            Node contextNode, String str, Node namespaceNode)
              throws TransformerException
    {
  
      // Have the XObject return its result as a NodeSetDTM.
      NodeIterator nl = selectNodeIterator(contextNode, str, namespaceNode);
  
      // Return the first node, or null
      return nl.nextNode();
    }
  
    /**
     *  Use an XPath string to select a nodelist.
     *  XPath namespace prefixes are resolved from the contextNode.
     *
     *  @param contextNode The node to start searching from.
     *  @param str A valid XPath string.
     *  @return A NodeIterator, should never be null.
     *
     * @throws TransformerException
     */
    public static NodeIterator selectNodeIterator(Node contextNode, String str)
            throws TransformerException
    {
      return selectNodeIterator(contextNode, str, contextNode);
    }
  
    /**
     *  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 str A valid XPath string.
     *  @param namespaceNode The node from which prefixes in the XPath will be resolved to namespaces.
     *  @return A NodeIterator, should never be null.
     *
     * @throws TransformerException
     */
    public static NodeIterator selectNodeIterator(
            Node contextNode, String str, Node namespaceNode)
              throws TransformerException
    {
  
      // Execute the XPath, and have it return the result
      XObject list = eval(contextNode, str, namespaceNode);
  
      // Have the XObject return its result as a NodeSetDTM.                
      return list.nodeset();
    }
  
    /**
     *  Use an XPath string to select a nodelist.
     *  XPath namespace prefixes are resolved from the contextNode.
     *
     *  @param contextNode The node to start searching from.
     *  @param str A valid XPath string.
     *  @return A NodeIterator, should never be null.
     *
     * @throws TransformerException
     */
    public static NodeList selectNodeList(Node contextNode, String str)
            throws TransformerException
    {
      return selectNodeList(contextNode, str, contextNode);
    }
  
    /**
     *  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 str A valid XPath string.
     *  @param namespaceNode The node from which prefixes in the XPath will be resolved to namespaces.
     *  @return A NodeIterator, should never be null.
     *
     * @throws TransformerException
     */
    public static NodeList selectNodeList(
            Node contextNode, String str, Node namespaceNode)
              throws TransformerException
    {
  
      // Execute the XPath, and have it return the result
      XObject list = eval(contextNode, str, namespaceNode);
  
      // Return a NodeList.
      return list.nodelist();
    }
  
    /**
     *  Evaluate XPath string to an XObject.  Using this method,
     *  XPath namespace prefixes will be resolved from the namespaceNode.
     *  @param contextNode The node to start searching from.
     *  @param str A valid XPath string.
     *  @return An XObject, which can be used to obtain a string, number, nodelist, etc, should never be null.
     *  @see org.apache.xpath.objects.XObject
     *  @see org.apache.xpath.objects.XNull
     *  @see org.apache.xpath.objects.XBoolean
     *  @see org.apache.xpath.objects.XNumber
     *  @see org.apache.xpath.objects.XString
     *  @see org.apache.xpath.objects.XRTreeFrag
     *
     * @throws TransformerException
     */
    public static XObject eval(Node contextNode, String str)
            throws TransformerException
    {
      return eval(contextNode, str, contextNode);
    }
  
    /**
     *  Evaluate XPath string to an XObject.
     *  XPath namespace prefixes are resolved from the namespaceNode.
     *  The implementation of this is a little slow, since it creates
     *  a number of objects each time it is called.  This could be optimized
     *  to keep the same objects around, but then thread-safety issues would arise.
     *
     *  @param contextNode The node to start searching from.
     *  @param str A valid XPath string.
     *  @param namespaceNode The node from which prefixes in the XPath will be resolved to namespaces.
     *  @return An XObject, which can be used to obtain a string, number, nodelist, etc, should never be null.
     *  @see org.apache.xpath.objects.XObject
     *  @see org.apache.xpath.objects.XNull
     *  @see org.apache.xpath.objects.XBoolean
     *  @see org.apache.xpath.objects.XNumber
     *  @see org.apache.xpath.objects.XString
     *  @see org.apache.xpath.objects.XRTreeFrag
     *
     * @throws TransformerException
     */
    public static XObject eval(Node contextNode, String str, Node namespaceNode)
            throws TransformerException
    {
  
      // Since we don't have a XML Parser involved here, install some default support
      // for things like namespaces, etc.
      // (Changed from: XPathContext xpathSupport = new XPathContext();
      //    because XPathContext is weak in a number of areas... perhaps
      //    XPathContext should be done away with.)
      // Create an XPathContext that doesn't support pushing and popping of
      // variable resolution scopes.  Sufficient for simple XPath 1.0 expressions.
      XPathContext xpathSupport = new XPathContext(false);
  
      // Create an object to resolve namespace prefixes.
      // XPath namespaces are resolved from the input context node's document element
      // if it is a root node, or else the current context node (for lack of a better
      // resolution space, given the simplicity of this sample code).
      PrefixResolverDefault prefixResolver = new PrefixResolverDefault(
        (namespaceNode.getNodeType() == Node.DOCUMENT_NODE)
        ? ((Document) namespaceNode).getDocumentElement() : namespaceNode);
  
      // Create the XPath object.
      XPath xpath = new XPath(str, null, prefixResolver, XPath.SELECT, null);
  
      // Execute the XPath, and have it return the result
      // return xpath.execute(xpathSupport, contextNode, prefixResolver);
      int ctxtNode = xpathSupport.getDTMHandleFromNode(contextNode);
  
      return xpath.execute(xpathSupport, ctxtNode, prefixResolver);
    }
  
    /**
     *   Evaluate XPath string to an XObject.
     *   XPath namespace prefixes are resolved from the namespaceNode.
     *   The implementation of this is a little slow, since it creates
     *   a number of objects each time it is called.  This could be optimized
     *   to keep the same objects around, but then thread-safety issues would arise.
     *
     *   @param contextNode The node to start searching from.
     *   @param str A valid XPath string.
     *   @param prefixResolver Will be called if the parser encounters namespace
     *                         prefixes, to resolve the prefixes to URLs.
     *   @return An XObject, which can be used to obtain a string, number, nodelist, etc, should never be null.
     *   @see org.apache.xpath.objects.XObject
     *   @see org.apache.xpath.objects.XNull
     *   @see org.apache.xpath.objects.XBoolean
     *   @see org.apache.xpath.objects.XNumber
     *   @see org.apache.xpath.objects.XString
     *   @see org.apache.xpath.objects.XRTreeFrag
     *
     * @throws TransformerException
     */
    public static XObject eval(
            Node contextNode, String str, PrefixResolver prefixResolver)
              throws TransformerException
    {
  
      // Since we don't have a XML Parser involved here, install some default support
      // for things like namespaces, etc.
      // (Changed from: XPathContext xpathSupport = new XPathContext();
      //    because XPathContext is weak in a number of areas... perhaps
      //    XPathContext should be done away with.)
      // Create the XPath object.
      XPath xpath = new XPath(str, null, prefixResolver, XPath.SELECT, null);
  
      // Create an XPathContext that doesn't support pushing and popping of
      // variable resolution scopes.  Sufficient for simple XPath 1.0 expressions.
      XPathContext xpathSupport = new XPathContext(false);
  
      // Execute the XPath, and have it return the result
      int ctxtNode = xpathSupport.getDTMHandleFromNode(contextNode);
  
      return xpath.execute(xpathSupport, ctxtNode, prefixResolver);
    }
  }
  