cdm/src/main/java/ucar/unidata/util/StringUtil2.java
static public String filter(String x, String okChars) {
    boolean ok = true;
    for (int pos = 0; pos < x.length(); pos++) {
      char c = x.charAt(pos);
      if (!(Character.isLetterOrDigit(c) || (0 <= okChars.indexOf(c)))) {
        ok = false;
        break;
      }
    }
    if (ok) {
      return x;
    }

    // gotta do it
    StringBuilder sb = new StringBuilder(x.length());
    for (int pos = 0; pos < x.length(); pos++) {
      char c = x.charAt(pos);
      if (Character.isLetterOrDigit(c) || (0 <= okChars.indexOf(c))) {
        sb.append(c);
      }
    }

    return sb.toString();
  }
static public String filter(String x, String okChars) {
    boolean ok = true;
    for (int pos = 0; pos < x.length(); pos++) {
      char c = x.charAt(pos);
      if (!(Character.isLetterOrDigit(c) || (0 <= okChars.indexOf(c)))) {
        ok = false;
        break;
      }
    }
    if (ok) {
      return x;
    }

    // gotta do it
    StringBuilder sb = new StringBuilder(x.length());
    for (int pos = 0; pos < x.length(); pos++) {
      char c = x.charAt(pos);
      if (Character.isLetterOrDigit(c) || (0 <= okChars.indexOf(c))) {
        sb.append(c);
      }
    }

    return sb.toString();
  }
Remove any char not alphanumeric or in okChars.

@param x       filter this string
@param okChars these are ok.
@return filtered string.