private String getRandomString(int length) {
    StringBuilder sb = new StringBuilder(length);
    for (int i = 0; i < length; i++) {
      sb.append(CHARACTERS.charAt(random.nextInt(CHARACTERS.length())));
    }
    return sb.toString();
  }
Gets a random string of size {@code length}.
@param length the size of the required random string.
@return a random string of size {@code length}.
ambry-tools/src/main/java/com/github/ambry/tools/perf/rest/PerfRouter.java