http://xml.apache.org/commons/components/external/: xml-commons provides an Apache-hosted set of DOM, SAX, and JAXP interfaces for use in other xml-based projects. Our hope is that we can standardize on both a common version and packaging scheme for these critical XML standards interfaces to make the lives of both our developers and users easier. The External Components portion of xml-commons contains interfaces that are defined by external standards organizations. For DOM, that's the W3C; for SAX it's David Megginson and sax.sourceforge.net; for JAXP it's Sun. 
/*
 * 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.
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// $Id: XPathVariableResolver.java 446598 2006-09-15 12:55:40Z jeremias $

package javax.xml.xpath;

import javax.xml.namespace.QName;


XPathVariableResolver provides access to the set of user defined XPath variables.


The XPathVariableResolver and the XPath evaluator must adhere to a contract that
cannot be directly enforced by the API.  Although variables may be mutable,
that is, an application may wish to evaluate the same XPath expression more
than once with different variable values, in the course of evaluating any
single XPath expression, a variable's value must be immutable.


Author: Norman Walsh,  Jeff Suttor
Version:$Revision: 446598 $, $Date: 2006-09-15 08:55:40 -0400 (Fri, 15 Sep 2006) $
Since:1.5
/**
 * <p><code>XPathVariableResolver</code> provides access to the set of user defined XPath variables.</p>
 *
 * <p>The <code>XPathVariableResolver</code> and the XPath evaluator must adhere to a contract that
 * cannot be directly enforced by the API.  Although variables may be mutable,
 * that is, an application may wish to evaluate the same XPath expression more
 * than once with different variable values, in the course of evaluating any
 * single XPath expression, a variable's value <strong><em>must</em></strong> be immutable.</p>
 *
 * @author  <a href="mailto:Norman.Walsh@Sun.com">Norman Walsh</a>
 * @author  <a href="mailto:Jeff.Suttor@Sun.com">Jeff Suttor</a>
 * @version $Revision: 446598 $, $Date: 2006-09-15 08:55:40 -0400 (Fri, 15 Sep 2006) $
 * @since 1.5
 */
public interface XPathVariableResolver {
  
Find a variable in the set of available variables.


If variableName is null, then a NullPointerException is thrown.


Params:
  • variableName – The QName of the variable name.
Throws:
Returns:The variables value, or null if no variable named variableName
  exists.  The value returned must be of a type appropriate for the underlying object model.
/** 
   * <p>Find a variable in the set of available variables.</p>
   * 
   * <p>If <code>variableName</code> is <code>null</code>, then a <code>NullPointerException</code> is thrown.</p>
   * 
   * @param variableName The <code>QName</code> of the variable name.
   * 
   * @return The variables value, or <code>null</code> if no variable named <code>variableName</code>
   *   exists.  The value returned must be of a type appropriate for the underlying object model.
   * 
   * @throws NullPointerException If <code>variableName</code> is <code>null</code>.
   */
  public Object resolveVariable(QName variableName);
}