public static String getHexString(byte[] b) throws Exception {
  String result = "";
  for (int i=0; i < b.length; i++) {
    result +=
          Integer.toString( ( b[i] & 0xff ) + 0x100, 16).substring( 1 );
  }
  return result;
}

import java.io.UnsupportedEncodingException;

public class StringUtils {

  static final byte[] HEX_CHAR_TABLE = {
    (byte)'0', (byte)'1', (byte)'2', (byte)'3',
    (byte)'4', (byte)'5', (byte)'6', (byte)'7',
    (byte)'8', (byte)'9', (byte)'a', (byte)'b',
    (byte)'c', (byte)'d', (byte)'e', (byte)'f'
  };

  private StringUtils () {}

  public static String getHexString(byte[] raw)
    throws UnsupportedEncodingException
  {
    byte[] hex = new byte[2 * raw.length];
    int index = 0;

    for (byte b : raw) {
      int v = b & 0xFF;
      hex[index++] = HEX_CHAR_TABLE[v >>> 4];
      hex[index++] = HEX_CHAR_TABLE[v & 0xF];
    }
    return new String(hex, "ASCII");
  }

  public static void main(String args[]) throws Exception{
    byte[] byteArray = {
      (byte)255, (byte)254, (byte)253,
      (byte)252, (byte)251, (byte)250
    };

    System.out.println(StringUtils.getHexString(byteArray));

    /*
     * output :
     *   fffefdfcfbfa
     */

  }
}

  static final String HEXES = "0123456789ABCDEF";
  public static String getHex( byte [] raw ) {
    if ( raw == null ) {
      return null;
    }
    final StringBuilder hex = new StringBuilder( 2 * raw.length );
    for ( final byte b : raw ) {
      hex.append(HEXES.charAt((b & 0xF0) >> 4))
         .append(HEXES.charAt((b & 0x0F)));
    }
    return hex.toString();
  }