Java生成包含大写字母，小写字母以及数字的随机密码

转自 https://www.cnblogs.com/dongliyang/archive/2013/04/01/2994554.html

具体原理是先保证有数字大小写字母，再随机生成剩下字符，再将所有字符随机交换位置，至于重不重复，我算了下至多76T数据后

代码如下：

import java.util.Random;

public final class PasswordUtils {
    private static Random random;
    private static long seed;

    static {
        seed = System.currentTimeMillis();
        random = new Random(seed);
    }

    private static int uniform(int N){
        return random.nextInt(N);
    }

    private static int uniform(int a,int b){
        return a + uniform(b - a);
    }

    public static String getGeneratePassword(){
        int len = 6;
        char[] chArr = new char[len];
        chArr[0] = (char)('0' + uniform(0,10));
        chArr[1] = (char)('A' + uniform(0,26));
        chArr[2] = (char)('a' + uniform(0,26));

        char[] codes = { '0','1','2','3','4','5','6','7','8','9',
                         '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','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'};

        for(int i = 3; i < len; i++){
            chArr[i] = codes[uniform(0,codes.length)];
        }

        for(int i = 0; i < len; i++){
            int r = i + uniform(len - i);
            char temp = chArr[i];
            chArr[i] = chArr[r];
            chArr[r] = temp;
        }

        return new String(chArr);
    }

    public static void main(String[] args) {
        for (int i = 0; i < 10000; i++) {
            System.out.println(getGeneratePassword());
        }
    }
}