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Chapter 3. Processing XML 61
implements the ContentHandler interface. To use DefaultHandler, create a
subclass and override the methods that interest you. The other methods can
safely be ignored, since they are just empty methods.
The ParserAdapter class makes a SAX1 Parser behave as a SAX2 XMLReader.
The XMLReaderAdapter class makes a SAX2 XML reader behave as a SAX1
parser. The two classes should ease the transition from SAX1 to SAX2 by
allowing SAX1 drivers and clients to co-exist with SAX2 drivers and clients in the
same application.
XML namespace support
SAX2 adds XML namespace support. Every implementation of the SAX2
XMLReader interface is required to support namespace processing in its default
state. Additionally, many XML readers allow namespace processing to be
modified or disabled. Namespace processing changes only element and attribute
naming, although it places restrictions on some other names. Each XML element
and attribute has a single name called the qName which may contain colons.
With namespaces, elements and attributes have two-part name, sometimes
called the universal or expanded name, which consists of a URI, and a
localName.
SAX2 is capable of supporting either of these views or both simultaneously.
Similarly, documents may use both views simultaneously. SAX2 XMLReader
implementations are required to report the namespace style names when
documents use them.
Namespace support affects the ContentHandler and Attributes interfaces. In
SAX2, the startElement and endElement callbacks in a content handler look like
Example 3-3 on page 61.
Example 3-3 SAX2 callback methods
public void startElement (String uri, String localName,String qName,
Attributes atts) throws SAXException;
public void endElement (String uri, String localName, String qName)
throws SAXException;
By default, an XML reader will report a namespace URI and a local name for
every element that belongs to a namespace, in both the start and end handler.
Consider Example 3-4 on page 61.
Example 3-4 Sample namespace
<html:hr xmlns:html="http://www.ibm.com"/>