Dangers of DOM
by, 04-27-2012 at 05:13 PM (604 Views)
At first glance, the DOM API seems to be more feature-rich, and therefore better, than the SAX API. However, DOM has serious efficiency problems that can hurt performance-sensitive applications.
The current group of XML parsers that support DOM implement the in-memory object model by creating many tiny objects that represent DOM nodes containing either text or other DOM nodes. This sounds natural enough, but has negative performance implications. One of the most expensive operations in Java is the new operator. Correspondingly, for every new operator executed in Java, the JVM garbage collector must eventually remove the object from memory when no references to the object remain. The DOM API tends to really thrash the JVM memory system with its many small objects, which are typically tossed aside soon after parsing.
Another DOM issue is the fact that it loads the entire XML document into memory. For large documents, this becomes a problem. Again, since the DOM is implemented as many tiny objects, the memory footprint is even larger than the XML document itself because the JVM stores a few extra bytes of information regarding all of these objects, as well as the contents of the XML document.