## javax.xml.xpath
Interface XPathFunctionResolver

public interface XPathFunctionResolver

`XPathFunctionResolver` provides access to the set of user defined `XPathFunction`s.

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.

Since:
  1.5
See Also:
  XML Path Language (XPath) Version 1.0, Core Function Library

Method Summary
`XPathFunction` `resolveFunction(QName functionName, int arity)` Find a function in the set of available functions.

Method Detail

### resolveFunction

    public XPathFunction resolveFunction(QName functionName,
                                         int arity)

  Find a function in the set of available functions.

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

  Parameters:
    `functionName` - The function name.
    `arity` - The number of arguments that the returned function must accept.
  Returns:
    The function or `null` if no function named `functionName` with `arity` arguments exists.
  Throws:
    `java.lang.NullPointerException` - If `functionName` or `arity` is `null`.