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XML: Another TLA or the Future?

XML (eXtensible Markup Language) is a widely-used W3C standard that is simple, flexible, and perfect for various applications. It serves as the backbone for technologies like SOAP and WSDL. Understanding XML is crucial for developers, as it plays a significant role in data interchange and configuration. Validating XML documents using a DTD ensures the structure's integrity, making it easier to manage complex data. This guide covers XML basics, parsing techniques (SAX and DOM), and practical examples to help you grasp this essential technology in the software landscape.

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XML: Another TLA or the Future?

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  1. XML: Another TLA or the Future? http://java.sun.com/xml/tutorial_intro.html • XML is eXtensible Markup Language • It's a w3c standard (what does this mean?) • http://www.w3.org/XML/ • It's simple, flexible, portable, extensible, hierarchical, complicated (see simple) • Basis for XMP-RPC, SOAP, UDDI, WSDL • Why do we need to understand XML? • It really is simple, and it really is powerful • It really is in-demand and one of the FOTDay

  2. XML in brief • Need some method to create XML • Exported by applications, e.g., iTunes • Edited by hand, this is a bad idea • Done programatically, see bullet 1 • XML can be validated with a DTD • Document Type Definition • Often provided by applications • Really necessary for complex XML data

  3. What does it look like? <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN "http://www.apple.com/DTDs/PropertyList-1.0.dtd"> <plist version="1.0"> <dict> <key>Major Version</key><integer>1</integer> <key>Minor Version</key><integer>1</integer> <key>Application Version</key><string>6.0.1</string> <key>Features</key><integer>1</integer> <key>MusicFolder</key> <string>file://localhost/Users/ola/Music/iTunes/iTunes%20Music/</string> <key>Library Persistent ID</key><string>2D2047AF6D8A9673</string> <key>Tracks</key> <dict> <key>40</key> <dict> <key>Track ID</key><integer>40</integer> <key>Name</key><string>Track 01</string> <key>Kind</key><string>AAC audio file</string>

  4. Elements of XML • There's an XML header, specifies global "stuff" • There's the content • Root element • Sub elements • What is an element? • Tagged, case-sensitive, semantic • Can contain text, data, attributes <project name="foo" type="java"> <file>Glob.java</file> <file>Blib.java</file> </project>

  5. Handling XML • There are two ways to parse/read XML • SAX: Simple API for XML • Stream based, register callbacks that are called when certain tags/data parsed • Can't move around, but can read and discard • DOM: Document Object Model • Entire tree-like structure read into memory • Easy to move around

  6. Saving and restoring objects • Classes should implement Serializable, this is a tag interface, not necessary to implement a function (see Cloneable) • mark non-serializable fields as transient • platform specific objects like font sizes, these need to be reconstructed rather than re-read • fields that aren’t needed when an object is deserialized • use ObjectOutputStream and ObjectInputStream, can customize behavior using private?! functions below private void writeObject(java.io.ObjectOutputStream out) throws IOException private void readObject(java.io.ObjectInputStream in) throws IOException, ClassNotFoundException; • also defaultReadObject() and defaultWriteObject()

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