This is a good point to review the packages that make up the Java XML library, their purpose, and their classes. The different package names reflect the different origins of the code. The Java interfaces came from Sun Microsystems, the DOM implementation came from the W3C, and the SAX parser implementation came from yet a third organization.
Package: javax.xml.parsers
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Purpose: Is the Java interface to the XML standard for parsing.
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Contains these classes/interfaces: DocumentBuilderFactory, DocumentBuilder, SAXParserFactory, SAXParser. These get instances of a Parser and undertake a parse on an XML file.
Package: javax.xml.transform
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Purpose: is the Java interface to the XML standard for tree transformation
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Contains: classes to convert an XML tree into an HTML file or XML with a different DTD. Tree transformation is beyond the scope of this text, but you can read more about it by searching for “transform” at java.sun.com.
Package: org.w3c.dom
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Purpose: has the classes that make up a DOM tree in memory
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Contains these classes/interfaces:
Nodeplus its subtypes:Document,DocumentType,Element, Entity,Attr,Text, etc.
Package: org.xml.sax
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Purpose: has the classes that can be used to navigate the data returned in a SAX parse
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Contains: two packages
org.xml.sax.ext(extensions) andorg.xml.sax.helpersplus these classes/interfaces:Attributes,ContentHandler,EntityResolver,DTDHandler,XMLReader. The helpers package contains theDefaultHandlerclass which is typically extended by one of your classes to handle a SAX parse, as explained below.
All the listed packages are kept in a file called jaxp.jar. The JAXP distribution also includes two other jar files: crimson.jar and xalan.jar. Crimson.jar holds the DOM and SAX parser implementations. Xalan.jar contains the implementation of the xml transformation interface. Make sure that the right jar files are in your path for the features you are using.
Because of the seemingly unrelated package names, XML parsing may appear a little unorganized. Just remember it this way: You always need the java.xml.parsers package. And you need the package with “dom” in its name to do a DOM parse, or “sax” in its name to do a SAX parse. The SAX packages also have the error-handling classes for both kinds of parse.