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 * reserved comment block

 * DO NOT REMOVE OR ALTER!

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/*

 * Copyright 1999-2004 The Apache Software Foundation.

 *

 * 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.

 */

/*

 * $Id: CachedXPathAPI.java,v 1.2.4.1 2005/09/10 03:47:42 jeffsuttor Exp $

 */

package com.sun.org.apache.xpath.internal;

import javax.xml.transform.TransformerException;

import com.sun.org.apache.xml.internal.utils.PrefixResolver;

import com.sun.org.apache.xml.internal.utils.PrefixResolverDefault;

import com.sun.org.apache.xpath.internal.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.

 *

 * This is an alternative for the old XPathAPI class, which provided

 * static methods for the purpose but had the drawback of

 * instantiating a new XPathContext (and thus building a new DTMManager,

 * and new DTMs) each time it was called. XPathAPIObject instead retains

 * its context as long as the object persists, reusing the DTMs. This

 * does have a downside: if you've changed your source document, you should

 * obtain a new XPathAPIObject to continue searching it, since trying to use

 * the old DTMs will probably yield bad results or malfunction outright... and

 * the cached DTMs may consume memory until this object and its context are

 * returned to the heap. Essentially, it's the caller's responsibility to

 * decide when to discard the cache.

 *

 * @see <a href="http://www.w3.org/TR/xpath">XPath Specification</a>

 * */

public class CachedXPathAPI

{

  /** XPathContext, and thus the document model system (DTMs), persists through multiple

      calls to this object. This is set in the constructor.

  */

  protected XPathContext xpathSupport;

  /**

   * <p>Default constructor. Establishes its own {@link XPathContext}, and hence

   * its own {@link com.sun.org.apache.xml.internal.dtm.DTMManager}.

   * Good choice for simple uses.</p>

   * <p>Note that any particular instance of {@link CachedXPathAPI} must not be

   * operated upon by multiple threads without synchronization; we do

   * not currently support multithreaded access to a single

   * {@link com.sun.org.apache.xml.internal.dtm.DTM}.</p>

   */

  public CachedXPathAPI()

  {

    xpathSupport = new XPathContext();

  }

  /**

   * <p>This constructor shares its {@link XPathContext} with a pre-existing

   * {@link CachedXPathAPI}.  That allows sharing document models

   * ({@link com.sun.org.apache.xml.internal.dtm.DTM}) and previously established location

   * state.</p>

   * <p>Note that the original {@link CachedXPathAPI} and the new one should

   * not be operated upon concurrently; we do not support multithreaded access

   * to a single {@link com.sun.org.apache.xml.internal.dtm.DTM} at this time.  Similarly,

   * any particular instance of {@link CachedXPathAPI} must not be operated

   * upon by multiple threads without synchronization.</p>

   * <p>%REVIEW% Should this instead do a clone-and-reset on the XPathSupport object?</p>

   *

   */

  public CachedXPathAPI(CachedXPathAPI priorXPathAPI)

  {

    xpathSupport = priorXPathAPI.xpathSupport;

  }

  /** Returns the XPathSupport object used in this CachedXPathAPI

   *

   * %REVIEW% I'm somewhat concerned about the loss of encapsulation

   * this causes, but the xml-security folks say they need it.

   * */

  public XPathContext getXPathContext()

  {

    return this.xpathSupport;

  }

  /**

   * 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  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  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  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  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  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  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 com.sun.org.apache.xpath.internal.objects.XObject

   *  @see com.sun.org.apache.xpath.internal.objects.XNull

   *  @see com.sun.org.apache.xpath.internal.objects.XBoolean

   *  @see com.sun.org.apache.xpath.internal.objects.XNumber

   *  @see com.sun.org.apache.xpath.internal.objects.XString

   *  @see com.sun.org.apache.xpath.internal.objects.XRTreeFrag

   *

   * @throws TransformerException

   */

  public  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 com.sun.org.apache.xpath.internal.objects.XObject

   *  @see com.sun.org.apache.xpath.internal.objects.XNull

   *  @see com.sun.org.apache.xpath.internal.objects.XBoolean

   *  @see com.sun.org.apache.xpath.internal.objects.XNumber

   *  @see com.sun.org.apache.xpath.internal.objects.XString

   *  @see com.sun.org.apache.xpath.internal.objects.XRTreeFrag

   *

   * @throws TransformerException

   */

  public  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 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 com.sun.org.apache.xpath.internal.objects.XObject

   *   @see com.sun.org.apache.xpath.internal.objects.XNull

   *   @see com.sun.org.apache.xpath.internal.objects.XBoolean

   *   @see com.sun.org.apache.xpath.internal.objects.XNumber

   *   @see com.sun.org.apache.xpath.internal.objects.XString

   *   @see com.sun.org.apache.xpath.internal.objects.XRTreeFrag

   *

   * @throws TransformerException

   */

  public  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);

    // Execute the XPath, and have it return the result

    XPathContext xpathSupport = new XPathContext();

    int ctxtNode = xpathSupport.getDTMHandleFromNode(contextNode);

    return xpath.execute(xpathSupport, ctxtNode, prefixResolver);

  }

}