An XPath object is
used to compile or evaluate an XPath expression. Create an
XPath object through an
XPathFactory. Configuration methods of
XPath allow you to specify an
XPathVariableResolver and an
XPathFunctionResolver to resolve variable and
function references in XPath expressions. You may also specify the
javax.xml.namespace.NamespaceContext with which
the XPath can resolve qualified names.
After creating and configuring an XPath object,
you can use the compile(
) method to compile an XPath expression
for later evaluation, or you can use one of the evaluate(
) methods to compile and evaluate an expression directly.
There are four versions of evaluate( ). All expect
a String containing an XPath expression as their
first argument. The second argument is the document or portion of a
document to evaluate the expression against. Two versions of
evaluate( ) expect an
org.xml.sax.InputSource for this second argument.
These versions of the method first parse the document and build a DOM
(or other object model) tree. The other two versions of
evaluate( ) expect an Object as
the second argument. The object passed should be a DOM (or other
object model) object representing the document or some portion of it.
For the org.w3c.dom object model, this might be a
Document, DocumentFragment,
Node, or NodeList object.
The final difference between evaluate( ) methods
is the presence or absence of a third argument. The two-argument
versions of evaluate( ) return the result of the
expression evaluation as a String. The
three-argument versions expect a third argument that specifies the
desired return type and return an Object of an
appropriate type. The valid types are the QName
objects defined in the XPathConstants class, such
as XPathConstants.NODE and
XPathConstants.NODESET. With the DOM object model,
evaluate( ) returns
org.w3c.dom.Node and
org.w3c.dom.NodeList objects for these types.
public interface
XPath {
// Public Instance Methods
XPathExpression
compile (String
expression ) throws XPathExpressionException;
String
evaluate (String
expression , Object
item ) throws XPathExpressionException;
String
evaluate (String
expression , org.xml.sax.InputSource
source )
throws XPathExpressionException;
Object
evaluate (String
expression , org.xml.sax.InputSource
source ,
javax.xml.namespace.QName
returnType )
throws XPathExpressionException;
Object
evaluate (String
expression , Object
item , javax.xml.namespace.
QName
returnType ) throws XPathExpressionException;
javax.xml.namespace.NamespaceContext
getNamespaceContext ( );
XPathFunctionResolver
getXPathFunctionResolver ( );
XPathVariableResolver
getXPathVariableResolver ( );
void
reset ( );
void
setNamespaceContext (javax.xml.namespace.NamespaceContext
nsContext );
void
setXPathFunctionResolver (XPathFunctionResolver
resolver );
void
setXPathVariableResolver (XPathVariableResolver
resolver );
}