Question

Scenario

I need to write a validation function that validates XML tag names (or attribute names) .

Eg.:

• "div" is valid
• "d<iv" is not valid
• "d\iv" is not valid

If a string is not valid i should escape that makes it invalid, and replace them with some arbitrary character (or remove it) .

Eg.:

• "d<iv" is not valid -> I replace it with "div" .

Those functions will be heavily called – so I need to take in consideration code effectiveness.

My problem(s)

• What are the rules that describe a valid XML tag/attribute name ? Is it safe to consider a valid XML tag/attribute to be described by the same rules as java variable name ? Or are those rules too restrictive ?
• Should I use the java regex package or I should write my own specialized method ? (As I said speed is important) .
• Do you have any suggestions ?

Thank you!

Answer 1

The rules are defined in the xml spec (look at the name definition)

If speed matters, then don’t use regular expressions. Do it more like this:

public static String correctName(String name) {
  StringBuilder nameBuilder = new StringBuilder();
  for (char nameChar:name.charArray())
     if (isValidXml(nameChar))          // some magic left to do ;)
         nameBuilder.append(nameChar);
  return nameBuilder.toString();
}

Note – the code above is a simple guideline, it does not cover the little annoyance, that the first char of an xml name has a different value range … if you want to correct illegal tags like $%&div then it’s a bit more complicated (more magic needed)