Despite the wide adoption of the Document Object Model (DOM) and the Simple API for XML (SAX), enterprise developers face the numerous shortcomings of these technologies almost daily.
Tutorial Details:
My last JavaWorld article "Simplify XML Processing with VTD-XML" looked at three important benefits of VTD-XML: performance, memory usage, and ease of use. VTD-XML makes XML applications not only easier to write, but also leaner and faster. XML applications written in VTD-XML are 10 times more responsive when compared to the same applications written with the Document Object Model (DOM) and are capable of serving 10 times the workload, while maintaining the same quality of services for proportionally bigger XML messages.
However, parsing is often only part of what needs to be done in an XML-based application; many applications change the XML data as well. Consider the following three use-cases involving XML content updates:
1. An address-book application internally saves data into XML format, and the user wants to update the contact information (e.g., a phone number)
2. An XML-enabled content switch inspects the incoming and outgoing SOAP messages and selectively turns on the values of mustUnderstand attributes in the SOAP header
3. An SOA (service-oriented architecture) security application canonicalizes a subset of XML data for the subsequent signing and encryption, then inserts the digest and ciphered text back into XML payload
The double whammy of updating XML with DOM or SAX
Unfortunately, DOM and SAX (Simple API for XML) tax application performance twice when applying changes to XML. First with parsing, which is notoriously slow and CPU intensive; even worse is the reserialization needed to generate updated XML. Consider modifying the text content of the following XML snippet from "red" to "blue."
red
Using DOM, you would have to go through the following three steps:
1. Build the DOM tree
2. Navigate to and then update the text node
3. Write the updated structure back into XML
SAX and Pull are not even worth mentioning here since neither provides you with the liberty to navigate the tree structure. If the XML file size increases, writing out updated XML—effectively, many string concatenations, buffer allocations, and encoding conversions—further degrades overall application performance already constrained by slow parsing.
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