String.replaceAll how far can you take it?

Question

Hi,
I want to do 2 (or 3) simple string conversions like this:
1. in: "CustomerOrderHistory" out: "customer_order_history"
2. in: "customer_order_history " out: either "CustomerOrderHistory" or "customerOrderHistory" (either ok)
Actually number 2 is no problem, I did it like this:
public static String mixedCaseToCaseInsensitiveLower (String input) {
     return input.replaceAll("([a-z])([A-Z])", "$1_$2").toLowerCase();           
}No problem works fine, but now I'm wondering if it's possible to implement case 1 in a one liner like that.
Of course, I I can see how I could code it with a specific routine, but I'd like to know if the replaceAll method can do it for me.
So far I have this:
return input.toLowerCase().replaceAll("((_)([a-z]))", "$1")This just removes any underscores that occur before a lower case character, but I don't see any way to tell it that the character after the underscore, ie "$1" should be upper cased.
It may be that I'm asking too much, or it may be that I've missed something... tell me what you think,
Thanks
Iain

Answer 1

You're asking too much. :/
You have to process the replacement text before it gets inserted into the result string, which means you can't use replaceAll(). You can, however, do it he long way, using Matcher's appendReplacement() and appendTail() methods:  private static Pattern p = Pattern.compile("(?:$|_)([a-z])");
  // to leave the first letter lowercase, use "_[a-z]"
  public static String toCamelCase(String input)
    Matcher m = p.matcher(input);
    StringBuffer sb = new StringBuffer();
    while (m.find())
      m.appendReplacement(sb, m.group(1).toUppercase());
    m.appendTail(sb);
    return sb.toString();
  }Of course, with about the same amount of effort, you do the same thing with indexOf(), charAt(), and a for loop. Now, if we could combine Matcher with the new Formatter (sprintf) class, we could really have some fun...