XML Processing With Java Overview

There’re basically two ways of processing xml with Java. One is the DOM way, that is tree-structure based way, and the other way is the SAX way that is event-driven stream based way. However, the bad thing is that there’re pros and cons for both ways, and the good thing is that we can use one of them in different situation to meet different needs.

The DOM way
DOM, Document Object Model, is the standard specification released by w3c consortium. It is a tree like structure which represents the structure of a XML document and is what what we often first parse a XML document into before we do any manipulation to it. It is quite intuitive for most programmers to manipulate. With it we can easily get what we want from a XML document, element names, attributes, values of elements, etc. But the price to pay is that before any manipulation we have to read the entire xml document and parse it into a DOM object during which everything must be stored in memory. This is inefficient and sometimes impossible, especially for extremely large documents. By the way, besides DOM, there’re some unofficially object models in use, such as JDOM, XOM, DOM4J and so on.

The SAX way
It is a stream like and event-based way. We can processing a document while we’re reading it. It is a very flexible but more complicated way than the DOM way. It is flexible because the SAX stream can be redirected to other process or document. It is complicated because the event handler (usually the DefaultHandler or ContentHandler) must be first written and then registered with the Parser (alternatively reader, or something like that). And there’re other disadvantages. Because it is processed like a stream, it is impossible to make changes to it or move backward to the data stream. But it is possilbe to make some simple structure (not the data itself) changes by using xsl transformation. In general, the SAX way is much faster than the DOM way.

What make up the “XML Processing”
So-called XML processing or sometimes called parsing consists of several aspects or procedures.
Validation
Data Modification and Retrieve
Transformation
Data Query

Examples

Higher Level Application
What are mentioned above are only those basic aspects about xml processing. Seen from a more global perspective, there’re many other higher level application of xml or xml processing.

Published temporarily and remains further refinement.