随机长度字符串

public static String getStrNumRandom(Integer length) {          StringBuilder str = new StringBuilder();        Random random = new Random();          for (int i = 0; i < length; i++) {              boolean b = random.nextBoolean();              if (b) { // 字符串                  int choice = random.nextBoolean() ? 65 : 97; //取得65大写字母还是97小写字母                  str.append((char) (choice + random.nextInt(26)));// 取得大写字母              } else { // 数字                  str.append(random.nextInt(10));              }          }          return str.toString();      }