How to get client mac address in Java

String getMacInfo(HttpServletRequest request)
    {
        //Get the IP address        String macInfo = null;
        try
        {
            String ip = ();
            //Get mac address under linux            macAddr = (ip);
            //Get mac address under windows            if((macAddr)){
                macAddr = (ip).trim();
            }
        }
        catch (Exception e)
        {
            ("Failed to get mac address");
            return null;
        }
        return macInfo;
    }

	// Get mac address from a Unix machine	 public static String getMac(String ip) throws IOException {
        String mac = ;
        if (ip != null) {
            try {
                Process process = ().exec("arp "+ip);
                InputStreamReader ir = new InputStreamReader(());
                LineNumberReader input = new LineNumberReader(ir);
                String line;
                StringBuffer s = new StringBuffer();
                while ((line = ()) != null) {
                    (line);
                }
                mac = ();
                if ((mac)) {
                    mac = ((":") - 2, (":") + 3);
                }
                return mac;
            } catch (Exception e) {
                ();
            }
        }
        return mac;
    }
    
    // Get the mac address from the windows machine	public static String getMacInWindows(final String ip) {
        String result = "";
        String[] cmd = {"cmd", "/c", "ping " + ip};
        String[] another = {"cmd", "/c", "ipconfig -all"};
        // Get the result after executing the command        String cmdResult = callCmd(cmd, another);
        // Get the mac address from the result of the previous step        result = filterMacAddress(ip, cmdResult, "-");
        return result;
 	}
 	
 	// Command execution 	public static String callCmd(String[] cmd, String[] another) {
        String result = "";
        String line = "";
        try {
            Runtime rt = ();
            // Execute the first command            Process proc = (cmd);
            ();
             // Execute the second command            proc = (another);
            InputStreamReader is = new InputStreamReader(());
            BufferedReader br = new BufferedReader(is);
            while ((line = ()) != null) {
                result += line;
            }
        } catch (Exception e) {
            ();
        }
        return result;
    }
	
	// Get the mac address	public static String filterMacAddress(final String ip, final String sourceString, final String macSeparator) {
        String result = "";
        String regExp = "((([0-9,A-F,a-f]{1,2}" + macSeparator + "){1,5})[0-9,A-F,a-f]{1,2})";
        Pattern pattern = (regExp);
        Matcher matcher = (sourceString);
        while (()) {
            result = (1);
            // Due to the problem of multiple network cards of the computer, the first mac address that is close to the IP is intercepted.            int num = (ip) - (": "+result + " ");
            if (num>0&&num<300) {
                break;
            }
        }
        return result;
    }