Formatting a byte array to string in java

Question

I am using this code to find the MAC address of a machine.This code prints directly the MAC address, but i want to return it as a string.I am completely confused.

please help.

try {
        InetAddress add = InetAddress.getByName("10.123.96.102");
        NetworkInterface ni1 = NetworkInterface.getByInetAddress(add);
        if (ni1 != null) {
            byte[] mac1 = ni1.getHardwareAddress();
            if (mac1 != null) {
                for (int k = 0; k < mac1.length; k++) {
                    System.out.format("%02X%s", mac1[k], (k < mac1.length - 1) ? "-" : "");
                }
            } else {
                System.out.println("Address doesn't exist ");
            }
            System.out.println();
        } else {
            System.out.println("address is not found.");
        }
    } catch (UnknownHostException e) {
        e.printStackTrace();
    } catch (SocketException e) {
        e.printStackTrace();
    }

Answer 1

Perhaps you could use Hex.encodeHex(bytes) from commons-codec.

Here are other ways to do this, without 3rd party libraries.

Answer 2

There is no standard text representation for Mac addresses. You just need to convert it to hex and separate the bytes for readability. Here is the function I use in the format of ifconfig on Unix,

public static String getMacAddress(String ipAddr)
        throws UnknownHostException, SocketException {
    InetAddress addr = InetAddress.getByName(ipAddr);
    NetworkInterface ni = NetworkInterface.getByInetAddress(addr);
    if (ni == null)
        return null;

    byte[] mac = ni.getHardwareAddress();
    if (mac == null)
        return null;

    StringBuilder sb = new StringBuilder(18);
    for (byte b : mac) {
        if (sb.length() > 0)
            sb.append(':');
        sb.append(String.format("%02x", b));
    }
    return sb.toString();
}

You just need to change the ':' to '-'.

Answer 3

  private static final byte[] NULL_MAC = new byte[] {0, 0, 0, 0, 0, 0};

  public static String getMacString(byte[] macAddress) {
    StringBuilder retval = new StringBuilder(17);
    if (macAddress == null) {
      macAddress = NULL_MAC;
    }
    boolean isFirst = true;
    for (byte b : macAddress) {
      if (!isFirst) {
        retval.append(":");
      } else {
        isFirst = false;
      }
      retval.append(String.format("%02x", b & 0xff));
    }
    return retval.toString();
  }