md5加密后字母分别以大写字母和小写字母显示

//以小写字母方式显示md5加密后的字符串

public static String md5(String str){
        try {
            MessageDigest md = MessageDigest.getInstance("MD5");
            md.update(str.getBytes());
            byte[] b = md.digest();
            StringBuffer sb = new StringBuffer();
            for (int i = 0; i < b.length; i++) {
                int v = (int) b[i];
                v = v < 0 ? 0x100 + v : v;
                String cc = Integer.toHexString(v);
                if (cc.length() == 1)
                    sb.append('0');
                sb.append(cc);
            }
            return sb.toString();
        }
        catch (Exception e) {
        }
        return "";
 }

//以大写字母方式显示md5加密后的字符串

public static String md5Capital(String s){
char hexDigits[] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' };
         try {
             byte[] strTemp = s.getBytes();
             //使用MD5创建MessageDigest对象
             MessageDigest mdTemp = MessageDigest.getInstance("MD5");
             mdTemp.update(strTemp);
             byte[] md = mdTemp.digest();
             int j = md.length;
             char str[] = new char[j * 2];
             int k = 0;
             for (int i = 0; i < j; i++) {
                 byte b = md[i];
                 //System.out.println((int)b);
                 //将没个数(int)b进行双字节加密
                 str[k++] = hexDigits[b >> 4 & 0xf];
                 str[k++] = hexDigits[b & 0xf];
             }
             return new String(str);
         } catch (Exception e) {return null;}
}

2、Java生成任意位数的字母数字组合随机数 //生成随机数字和字母, length为位数

public String getStringRandom(int length) {
    String val = “”;
    Random random = new Random();
    // 参数length，表示生成几位随机数
    for (int i = 0; i < length; i++) {
        String charOrNum = random.nextInt(2) % 2 == 0 ? “char” : “num”;
        // 输出字母还是数字
        if (“char”.equalsIgnoreCase(charOrNum)) {
            // 输出是大写字母还是小写字母
           int temp = random.nextInt(2) % 2 == 0 ? 65 : 97;
           val += (char) (random.nextInt(26) + temp);
        } else if (“num”.equalsIgnoreCase(charOrNum)) {
           val += String.valueOf(random.nextInt(10));
        }
    }
    return val;
}