@Test

    public void getRamdonString() {

        final int maxNum = 36;

        int i; // 生成的随机数

        int count = 0; // 生成的密码的长度

        char[] str = {'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's',

                't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9'};

        StringBuffer pwd = new StringBuffer("");

        Random r = new Random();

        while (count < maxNum) {

            // 生成随机数，取绝对值，防止生成负数，

            i = Math.abs(r.nextInt(50)); // 生成的数最大为36-1

            if (i >= 0 && i < str.length) {

                pwd.append(str[i]);

                count++;

            }

        }

        System.out.println(pwd);

    }

    @Test

    public void getRamdonString2() {

        StringBuffer sb = new StringBuffer();

        String ALLCHAR = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";

        Random random = new Random();

        for (int i = 0; i < 20; i++) {

            sb.append(ALLCHAR.charAt(random.nextInt(ALLCHAR.length())));

        }

        System.out.println(sb.toString());

    }