why is sax parsing faster than dom parsing ? and how does stax work?

Assuming you do nothing but parse the document, the ranking of the different parser standards is as follows:

1. StAX is the fastest

• The event is reported to you

2. SAX is next

• It does everything StAX does plus the content is realized automatically (element name, namespace, attributes, ...)

3. DOM is last

• It does everything SAX does and presents the information as an instance of Node.

Your Use Case

• If you need to maintain all of the XML, DOM is the standard representation. It integrates cleanly with XSLT transforms (javax.xml.transform), XPath (javax.xml.xpath), and schema validation (javax.xml.validation) APIs. However if performance is key, you may be able to build your own tree structure using StAX faster than a DOM parser could build a DOM.

DOM parsing requires you to load the entire document into memory and then traverse a tree to find the information you want.

SAX only requires as much memory as you need to do basic IO, and you can extract the information that you need as the document is being read. Because SAX is stream oriented, you can even process a file which is still being written by another process.

SAX is faster because DOM parsers often use a SAX parser to parse a document internally, then do the extra work of creating and manipulating objects to represent each and every node, even if the application doesn't care about them.

An application that uses SAX directly is likely to utilize the information set more efficiently than a DOM "parser" does.

StAX is a happy medium where an application gets a more convenient API than SAX's event-driven approach, yet doesn't suffer the inefficiency of creating a complete DOM.