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package javax.xml.xpath;

import javax.xml.namespace.QName;


XPathFunctionResolver provides access to the set of user defined XPathFunctions.


XPath functions are resolved by name and arity.
The resolver is not needed for XPath built-in functions and the resolver
cannot be used to override those functions.


In particular, the resolver is only called for functions in an another
namespace (functions with an explicit prefix). This means that you cannot
use the XPathFunctionResolver to implement specifications
like XML-Signature Syntax
and Processing which extend the function library of XPath 1.0 in the
same namespace. This is a consequence of the design of the resolver.


If you wish to implement additional built-in functions, you will have to
extend the underlying implementation directly.


Author: Norman Walsh,  Jeff Suttor
See Also:
Since:1.5
/**
 * <p><code>XPathFunctionResolver</code> provides access to the set of user defined <code>XPathFunction</code>s.</p>
 *
 * <p>XPath functions are resolved by name and arity.
 * The resolver is not needed for XPath built-in functions and the resolver
 * <strong><em>cannot</em></strong> be used to override those functions.</p>
 *
 * <p>In particular, the resolver is only called for functions in an another
 * namespace (functions with an explicit prefix). This means that you cannot
 * use the <code>XPathFunctionResolver</code> to implement specifications
 * like <a href="http://www.w3.org/TR/xmldsig-core/">XML-Signature Syntax
 * and Processing</a> which extend the function library of XPath 1.0 in the
 * same namespace. This is a consequence of the design of the resolver.</p>
 *
 * <p>If you wish to implement additional built-in functions, you will have to
 * extend the underlying implementation directly.</p>
 *
 * @author  <a href="mailto:Norman.Walsh@Sun.com">Norman Walsh</a>
 * @author  <a href="mailto:Jeff.Suttor@Sun.com">Jeff Suttor</a>
 * @see <a href="http://www.w3.org/TR/xpath#corelib">XML Path Language (XPath) Version 1.0, Core Function Library</a>
 * @since 1.5
 */
public interface XPathFunctionResolver {
  
Find a function in the set of available functions.


If functionName or arity is null, then a NullPointerException is thrown.


Params:
  • functionName – The function name.
  • arity – The number of arguments that the returned function must accept.
Throws:
Returns:The function or null if no function named functionName with arity arguments exists.
/**
   * <p>Find a function in the set of available functions.</p>
   *
   * <p>If <code>functionName</code> or <code>arity</code> is <code>null</code>, then a <code>NullPointerException</code> is thrown.</p>
   *
   * @param functionName The function name.
   * @param arity The number of arguments that the returned function must accept.
   *
   * @return The function or <code>null</code> if no function named <code>functionName</code> with <code>arity</code> arguments exists.
   *
   * @throws NullPointerException If <code>functionName</code> or <code>arity</code> is <code>null</code>.
   */
  public XPathFunction resolveFunction(QName functionName, int arity);
}