MD5(Message Digest algorithm 5，信息摘要算法)

private String MD5(String s) {
    try {
        MessageDigest md = MessageDigest.getInstance("MD5");
        byte[] bytes = md.digest(s.getBytes("utf-8"));
        return toHex(bytes);
    }
    catch (Exception e) {
        throw new RuntimeException(e);
    }
}

private static String toHex(byte[] bytes) {

    final char[] HEX_DIGITS = "0123456789ABCDEF".toCharArray();
    StringBuilder ret = new StringBuilder(bytes.length * 2);
    for (int i=0; i<bytes.length; i++) {
        ret.append(HEX_DIGITS[(bytes[i] >> 4) & 0x0f]);
        ret.append(HEX_DIGITS[bytes[i] & 0x0f]);
    }
    return ret.toString();
}