public static String getRandomText(int length) {

    String base = "abcdefghijklmnopqrstuvwxyz0123456789";
    StringBuilder st = new StringBuilder();
    for (int i = 0; i < length; i++) {
      int number = random.nextInt(base.length());
      st = st.append(base.charAt(number));
    }
    return st.toString();
  }
get random text consisting of lowercase letters and numbers.

@param length -the size of random text
iotdb-core/datanode/src/test/java/org/apache/iotdb/db/utils/RandomNum.java