public class Test {

    /**
     * m进制n位随机字符串生成方法
     * m:大小写字母+数字生成26+26+9=61，所以可采用62进制（例子）
     * n:生成随机串的位数（以下以6位字符串为例）
     */
    private static long minValue = 1000000000L; // 62^5 = 916132832,为了防止生成的短码太规律，设置初始值从1000000000L(10亿)开始
    private static long maxValue = 56800235584L; // 62^6 = 56800235584L （568亿）
    private static String elements = "G86futKrpN2OgZhTmHX0EiyDnqRvxdCa1SYLQVUzB475IM39ocPJwejkbWslAF";

    public static void main(String[] args) {
        for (long i = minValue; i < minValue+10; i++) {
            System.out.println(generateStr(i));
        }
    }

    public static String generateStr(long seq) {
        if (seq < minValue || seq > maxValue) {
            System.out.println("超出随机串生成数量！");
            return null;
        }

        StringBuilder sb = new StringBuilder();
        do {
            int i = (int) (seq % 62);
            sb.append(elements.charAt(i));
            seq /= 62;
        } while (seq > 0);
        return sb.reverse().toString();
    }
}

输出结果：

Connected to the target VM, address: '127.0.0.1:59315', transport: 'socket'
8t4k7m
8t4k7H
8t4k7X
8t4k70
8t4k7E
8t4k7i
8t4k7y
8t4k7D
8t4k7n
8t4k7q
Disconnected from the target VM, address: '127.0.0.1:59315', transport: 'socket'

Process finished with exit code 0