//第一种随机字母数字生成private static String reduceNum() {    //定义一个字符串（A-Z，a-z，0-9）即62位；    String str = "zxcvbnmlkjhgfdsaqwertyuiopQWERTYUIOPASDFGHJKLZXCVBNM1234567890";    //由Random生成随机数    Random random = new Random();    StringBuffer buffer = new StringBuffer();    //生成一个长度为7的字符串    for (int i = 0; i < 7; i++) {        //产生0-61个数字        int num = random.nextInt(62);        //将产生的数字循环7次存放进StringBuffer中        buffer.append(str.charAt(num));    }    //将StringBuffer转换成string    return buffer.toString();}

//第二种随机字母数字生成public String getRandom(int length) {    String str = "";    Random ran = new Random();    //参数length,表示生成几位数    for (int i = 0; i < length; i++) {        String charOrNum = ran.nextInt(2) % 2 == 0 ? "char" : "num";        //输出字母还是数字        if ("char".equalsIgnoreCase(charOrNum)) {            //输出大写字母还是小写字母            int temp = ran.nextInt(2) % 2 == 0 ? 65 : 97;            str += (char) (ran.nextInt(26) + temp);        } else if ("num".equalsIgnoreCase(charOrNum)) {            str += String.valueOf(ran.nextInt(10));        }    }    return str;}

@Testpublic void run2() {    String random = getRandom(7);    String s = reduceNum();    System.out.println(random);    System.out.println(s);}