Java Reference
In-Depth Information
System.err.println("FCE: "+fce);
}
catch (ParserConfigurationException pce)
{
System.err.println("PCE: "+pce);
}
catch (XPathException xpe)
{
System.err.println("XPE: "+xpe);
}
}
}
After parsing
contacts.xml
and building the DOM tree,
main()
instantiates
XPathFactory
by calling its
XPathFactory newInstance()
method. The
resulting
XPathFactory
instance can be used to set features (such as secure pro-
cessing, to process XML documents securely) by calling its
void
setFeature(String name, boolean value)
method,createan
XPath
ob-
ject by calling its
XPath newXPath()
method, and more.
XPath
declares an
XPathExpression compile(String expression)
methodforcompilingthespecified
expression
(anXPathexpression)andreturning
thecompiledexpressionasaninstanceofaclassthatimplementsthe
XPathExpres-
sion
interface.Thismethodthrows
XPathExpressionException
(asubclassof
XMLException
) when the expression cannot be compiled.
XPath
also declares several overloaded
evaluate()
methods for immediately
evaluatinganexpressionandreturningtheresult.Becauseitcantaketimetoevaluatean
expression,youmightchoosetocompileacomplexexpressionfirst(toboostperform-
ance) when you plan to evaluate this expression many times.
After compiling the expression,
main()
calls
XPathExpression
's
Object
evaluate(Object item, QName returnType)
method to evaluate the ex-
pression.Thefirstargumentisthecontextnodefortheexpression,whichhappenstobe
a
Document
instanceintheexample.Thesecondargumentspecifiesthekindofobject
returned by
evaluate()
and is set to
XPathConstants.NODESET
, a qualified
namefortheXPath1.0nodesettype,whichisimplementedviaDOM's
NodeList
in-
terface.
