Parsing XML strings in MATLAB

Question

I need to parse an XML string with MATLAB (caution: without file I/O, so I don't want to write the string to a file and then read them). I'm receiving the strings from an HTTP connection and the parsing should be very fast. I'm mostly concerned about reading the values of certain tags in the entire string

The net is full of death threats about parsing XML with regexp so I didn't want to get into that just yet. I know MATLAB has seamless java integration but I'm not very java savvy. Is there a quick way to get certain values from XML very very rapidly?

For example I want to get the 'volume' information from this string below and write this to a variable.

<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>


<root>
  <volume>256</volume>
  <length>0</length>
  <time>0</time>
  <state>stop</state>
  ....

Answer 1

There's an entire class of functions for dealing with xml, including xmlread and xmlwrite. Those should be pretty useful for your problem.

Answer 2

For what it's worth, below is the Matlab executable Java code to perform the required task, without writing to an intermediate file:

%An XML formatted string
strXml = [...
    '<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>' char(10)...
    '<root>' char(10) ...
    '  <volume>256</volume>' char(10) ...
    '  <length>0</length>' char(10) ...
    '  <time>0</time>' char(10) ...
    '  <state>stop</state>' char(10) ...
    '</root>' ];

%"simple" java code to create a document from said string
xmlDocument = javax.xml.parsers.DocumentBuilderFactory.newInstance().newDocumentBuilder.parse(java.io.StringBufferInputStream(strXml));

%"intuitive" methods to explore the xmlDocument
nodeList = xmlDocument.getElementsByTagName('volume');
numberOfNodes = nodeList.getLength();

firstNode = nodeList.item(0);
firstNodeContent = firstNode.getTextContent;

disp(firstNodeContent);  %Returns '256'

---

As an alternative, if your application allows it, consider passing the URL directly into your XML parser. Untested java code is below, but that probably also opens up the Matlab built-in xslt function as well.

xmlDocument = javax.xml.parsers.DocumentBuilderFactory.newInstance().newDocumentBuilder.parse('URL_AS_A_STRING_HERE');

Documentation here. Start at the "javax.xml.parsers" package.