public static String getRandomString(int length) { //length表示生成字符串的长度

    String base = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";

    Random random = new Random();

    StringBuffer sb = new StringBuffer();

    for (int i = 0; i < length; i++) {

        int number = random.nextInt(base.length());

        sb.append(base.charAt(number));

    }

    return sb.toString();

 }