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Understanding JDOM: A Java-centric Approach to XML Handling

This presentation introduces JDOM, a convenient and efficient Java library for XML document manipulation. Unlike DOM and SAX, JDOM focuses on offering a straightforward API that simplifies XML processing for Java developers. It integrates seamlessly with DOM and SAX while prioritizing ease of use through features like method overloading and type conversions. Participants will learn about JDOM's philosophy, benefits, and overall structure, as well as how it can streamline XML handling in Java applications.

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Understanding JDOM: A Java-centric Approach to XML Handling

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Presentation Transcript

  1. Acknowledgments This PowerPoint is based on slides from: Jason Hunter and Brett McLaughlin

  2. Java + XML = JDOM Webprogramming (WEBP) 2. Mar. 2010 By Henrik Høltzer

  3. What is JDOM? • JDOM is a way to represent an XML document for easy and efficient reading, manipulation, and writing • Straightforward API • Lightweight and fast • Java-optimized • Despite the name similarity, it's not built on DOM or modeled after DOM • An open source project with an Apache-style license • 950 developers on jdom-interest (high traffic) • 800 lurkers on jdom-announce (low traffic)

  4. The JDOM Philosophy • JDOM should be straightforward for Java programmers • Use the power of the language (Java 2) • Take advantage of method overloading, the Collections APIs, reflection, weak references • Provide conveniences like type conversions • JDOM should hide the complexities of XML wherever possible • An Element has text content, not a child Text node with content • Exceptions should contain useful error messages • Give line numbers and specifics, use no SAX or DOM specifics

  5. More JDOM Philosophy • JDOM should integrate with DOM and SAX • Reads and writes DOM docs and SAX events • Can use anyDOM or SAX parser (uses adapter model or can use JAXP) • Why not use DOM: • Same API on multiple languages, defined using IDL • Foreign to the Java environment, Java programmer • Fairly heavyweight in memory • Why not use SAX: • No document modification, random access, or output • Fairly steep learning curve to use correctly • JDOM is to DOM/SAX as RMI is to CORBA • Java optimized, plays well with the other

  6. The org.jdom.input Package • Classes for reading XML from existing sources: • DOMBuilder • SAXBuilder • Also, outside contributions in jdom-contrib: • ResultSetBuilder • SpitfireBuilder

  7. The org.jdom.output Package • Classes for writing XML to various forms of output: • DOMOutputter • SAXOutputter • XMLOutputter • Also, outside contributions in jdom-contrib: • JTreeOutputter

  8. General Program Flow • Normally XML Document -> SAXBuilder -> XMLOutputter XML Document Direct Build XMLOutputter SAXBuilder SAXOutputter JDOM Document DOMBuilder DOMOutputter DOM Node(s)

  9. The Document lifecycle • Documents are rep. by the org.jdom.Document class • A lightweight object holding a DocType, ProcessingInstructions, a root Element (containing other Elements), and Comments • A document can be constructed from scratch: • Or it can be constructed from a file, stream, or URL: • Then it can be output as XML, or SAX, or DOM: Document doc = new Document( new Element("root").setText("courseregister")); SAXBuilder builder = new SAXBuilder(); Document doc = builder.build(url); XMLOutputter outputter = new XMLOutputter(); outputter.output(doc, System.out);

  10. Ensuring Well-Formedness • The Element constructor (and all other object constructors) check to make sure the element is legal • i.e. the name and content don't contain inappropriate characters • The add and remove methods also check document structure • An element may only exist at one point in the tree • Only one value can be returned by getParent() • No loops in the graph are allowed • Exactly one root element must exist

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