Java Reference
In-Depth Information
The
getNamespaceURI()
method is passed a
prefix
argument that must be
mappedtoaURI.Ifthisargumentis
null
,an
IllegalArgumentException
ob-
ject must be thrown (according to the Java documentation). When the argument is the
desired prefix value, the namespace URI is returned.
Afterinstantiatingthe
XPath
class,youwouldinstantiate
NSContext
andregister
this instance with the
XPath
instance by calling
XPath
's
void
setNamespaceContext(NamespaceContext nsContext)
method.Forex-
ample, you would specify
xp.setNamespaceContext(new NSContext());
after
XPath xp = xpf.newXPath();
toregisterthe
NSContext
instancewith
xp
.
All that's left to accomplish is to apply the prefix to the XPath expression, which
now becomes
//tt:contact[tt:city='Chicago']/tt:name/text()
be-
causethe
contact
,
city
,and
name
elementsarenowpartofthedefaultnamespace,
whose URI is mapped to arbitrary prefix
tt
in the
NSContext
instance's
getNamespaceURI()
method.
Compileandruntherevised
XPathSearch
applicationandyou'llsee
John Doe
followed by
Bob Jones
on separate lines.
Extension Functions and Function Resolvers
The XPath API lets you define functions (via Java methods) that extend XPath's pre-
defined function repertoire by offering new features not already provided. These Java
methods cannot have side effects because XPath functions can be evaluated multiple
timesandinanyorder.Furthermore,theycannotoverridepredefinedfunctions;aJava
method with the same name as a predefined function is never executed.
that records a contact's date of birth information in YYYY-MM-DD format.
Listing
10-24
shows the resulting XML file.
Listing 10-24.
XML-based contacts database with birth information
<?xml version="1.0"?>
<contacts xmlns="http://www.tutortutor.ca/">
<contact>
<name>John Doe</name>
<birth>1953-01-02</birth>
<city>Chicago</city>
<city>Denver</city>
