1 /*
   2  * Copyright (c) 2003, 2005, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package javax.xml.xpath;
  27 
  28 import javax.xml.namespace.QName;
  29 
  30 /**
  31  * <p><code>XPathFunctionResolver</code> provides access to the set of user defined <code>XPathFunction</code>s.</p>
  32  *
  33  * <p>XPath functions are resolved by name and arity.
  34  * The resolver is not needed for XPath built-in functions and the resolver
  35  * <strong><em>cannot</em></strong> be used to override those functions.</p>
  36  *
  37  * <p>In particular, the resolver is only called for functions in an another
  38  * namespace (functions with an explicit prefix). This means that you cannot
  39  * use the <code>XPathFunctionResolver</code> to implement specifications
  40  * like <a href="http://www.w3.org/TR/xmldsig-core/">XML-Signature Syntax
  41  * and Processing</a> which extend the function library of XPath 1.0 in the
  42  * same namespace. This is a consequence of the design of the resolver.</p>
  43  *
  44  * <p>If you wish to implement additional built-in functions, you will have to
  45  * extend the underlying implementation directly.</p>
  46  *
  47  * @author  Norman Walsh
  48  * @author  Jeff Suttor
  49  * @see <a href="http://www.w3.org/TR/xpath#corelib">XML Path Language (XPath) Version 1.0, Core Function Library</a>
  50  * @since 1.5
  51  */
  52 public interface XPathFunctionResolver {
  53   /**
  54    * <p>Find a function in the set of available functions.</p>
  55    *
  56    * <p>If <code>functionName</code> or <code>arity</code> is <code>null</code>, then a <code>NullPointerException</code> is thrown.</p>
  57    *
  58    * @param functionName The function name.
  59    * @param arity The number of arguments that the returned function must accept.
  60    *
  61    * @return The function or <code>null</code> if no function named <code>functionName</code> with <code>arity</code> arguments exists.
  62    *
  63    * @throws NullPointerException If <code>functionName</code> or <code>arity</code> is <code>null</code>.
  64    */
  65   public XPathFunction resolveFunction(QName functionName, int arity);
  66 }
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