JAXP is an XML framework by SUN that allows programmers to
plug-in any W3C compliant XML parser using
Java's system property files. It is not a parser by itself, but provides a level of abstraction by facilitating dynamic parser selection. From an architectural perspective JAXP sits between the actual XML parser and your application.
JDOM is another XML framework that integrates standard Java collection classes with any W3C compliant DOM parser allowing programmers to manipulate DOM objects as Java Collections. Very much like JAXP, JDOM sits between the application and the parser. Note that JDOM by itself is not an XML parser.
Hope that helps!
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Ajith Kallambella M. Sun Certified Programmer for the Java�2 Platform.
IBM Certified Developer - XML and Related Technologies, V1.