Url Encode function. Encode a string according to W3C standards

this is a function that turns all the chars in a string to the W3C Standards. 

/**
  * Encode a string according to W3C standards.
  *
  */
 public static String urlEncoder(String s) {
  if (s == null)
   return s;
  StringBuffer sb = new StringBuffer(s.length() * 3);
  try {
   char c;
   for (int i = 0; i < s.length(); i++) {
    c = s.charAt(i);
    if (c == '&') {
     sb.append("&amp;");
    } else if (c == ' ') {
     sb.append('+');
    } else if (
     (c >= ',' && c <= ';')
       (c >= 'A' && c <= 'Z')
       (c >= 'a' && c <= 'z')
       c == '_'
       c == '?') {
     sb.append(c);
    } else {
     sb.append('%');
     if (c > 15) { // is it a non-control char, ie. >x0F so 2 chars
      sb.append(Integer.toHexString((int)c)); // just add % and the string
     } else {
      sb.append("0" + Integer.toHexString((int)c));
      // otherwise need to add a leading 0
     }
    }
   }

  } catch (Exception ex) {
   return (null);
  }
  return (sb.toString());
 }

source of this function : http://forum.java.sun.com/thread.jspa?threadID=594204&messageID=3596899