生成8-20位随机密码（大小写字母、数字、特殊字符）

大写字母：ABCDEFGHIJKLMNOPQRSTUVWXYZ
小写字母：abcdefghijklmnopqrstuvwxyz
数字：0123456789
特殊字符：!"#$%&'()*+,-./:;<=>?@[]^_`{|}~
以上四种全部包括
上代码

public static String getRandomPassword() {
        int len = (int) (8 + Math.random() * (20 - 8 + 1));
        String result = null;
        while (len > 7) {
            result = makeRandomPassword(len);
            if (result.matches(".*[a-z]{1,}.*") && result.matches(".*[A-Z]{1,}.*") && result.matches(".*\\d{1,}.*") && result.matches(".*[!\"#$%&'\\()*+,\\-./:;<=>?@\\[\\]^_`{|}~]{1,}.*")) {
                return result;
            }
            result = makeRandomPassword(len);
        }
        return null;
    }

    public static String makeRandomPassword(int len) {
        char charr[] = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890!\"#$%&'()*+,-./:;<=>?@[\\]^_`{|}~)".toCharArray();
        StringBuilder sb = new StringBuilder();
        Random random = new Random();
        for (int i = 0; i < len; ++i) {
            sb.append(charr[random.nextInt(charr.length)]);
        }
        return sb.toString();
    }