src/org/apache/xml/utils/PrefixResolverDefault.java

/*
 * The Apache Software License, Version 1.1
 *
 *
 * Copyright (c) 1999 The Apache Software Foundation.  All rights 
 * reserved.
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 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
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 *
 * 1. Redistributions of source code must retain the above copyright
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 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
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 * 5. Products derived from this software may not be called "Apache",
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 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation and was
 * originally based on software copyright (c) 1999, Lotus
 * Development Corporation., http://www.lotus.com.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */
package org.apache.xml.utils;

import org.w3c.dom.Node;
import org.w3c.dom.NamedNodeMap;

/**
 * <meta name="usage" content="general"/>
 * This class implements a generic PrefixResolver that
 * can be used to perform prefix-to-namespace lookup
 * for the XPath object.
 */
public class PrefixResolverDefault implements PrefixResolver
{

  /**
   * The context to resolve the prefix from, if the context
   * is not given.
   */
  Node m_context;

  /**
   * The URI for the XML namespace.
   * (Duplicate of that found in org.apache.xpath.XPathContext).
   */
  public static final String S_XMLNAMESPACEURI =
    "http://www.w3.org/XML/1998/namespace";

  /**
   * Construct a PrefixResolverDefault object.
   * @param xpathExpressionContext The context from
   * which XPath expression prefixes will be resolved.
   * Warning: This will not work correctly if xpathExpressionContext
   * is an attribute node.
   * @param xpathExpressionContext Node from which to start searching for a
   * xmlns attribute that binds a prefix to a namespace (when the namespace
   * context is not specified in the getNamespaceForPrefix call).
   */
  public PrefixResolverDefault(Node xpathExpressionContext)
  {
    m_context = xpathExpressionContext;
  }

  /**
   * Given a namespace, get the corrisponding prefix.  This assumes that
   * the PrevixResolver hold's it's own namespace context, or is a namespace
   * context itself.
   * @param prefix Prefix to resolve.
   * @return Namespace that prefix resolves to, or null if prefix
   * is not bound.
   */
  public String getNamespaceForPrefix(String prefix)
  {
    return getNamespaceForPrefix(prefix, m_context);
  }

  /**
   * Given a namespace, get the corrisponding prefix.
   * Warning: This will not work correctly if namespaceContext
   * is an attribute node.
   * @param prefix Prefix to resolve.
   * @param namespaceContext Node from which to start searching for a
   * xmlns attribute that binds a prefix to a namespace.
   * @return Namespace that prefix resolves to, or null if prefix
   * is not bound.
   */
  public String getNamespaceForPrefix(String prefix,
                                      org.w3c.dom.Node namespaceContext)
  {

    Node parent = namespaceContext;
    String namespace = null;

    if (prefix.equals("xml"))
    {
      namespace = S_XMLNAMESPACEURI;
    }
    else
    {
      int type;

      while ((null != parent) && (null == namespace)
             && (((type = parent.getNodeType()) == Node.ELEMENT_NODE)
                 || (type == Node.ENTITY_REFERENCE_NODE)))
      {
        if (type == Node.ELEMENT_NODE)
        {
          NamedNodeMap nnm = parent.getAttributes();

          for (int i = 0; i < nnm.getLength(); i++)
          {
            Node attr = nnm.item(i);
            String aname = attr.getNodeName();
            boolean isPrefix = aname.startsWith("xmlns:");

            if (isPrefix || aname.equals("xmlns"))
            {
              int index = aname.indexOf(':');
              String p = isPrefix ? aname.substring(index + 1) : "";

              if (p.equals(prefix))
              {
                namespace = attr.getNodeValue();

                break;
              }
            }
          }
        }

        parent = parent.getParentNode();
      }
    }

    return namespace;
  }

  /**
   * Return the base identifier.
   *
   * @return null
   */
  public String getBaseIdentifier()
  {
    return null;
  }
}