public static String md5(String string) {
  if (TextUtils.isEmpty(string)) {
   return "";
  }
  MessageDigest md5 = null;
  try {
   md5 = MessageDigest.getInstance("MD5");
   byte[] bytes = md5.digest(string.getBytes());
   String result = "";
   for (byte b : bytes) {
    String temp = Integer.toHexString(b & 0xff);
    if (temp.length() == 1) {
     temp = "0" + temp;
    }
    result += temp;
   }
   return result;
  } catch (NoSuchAlgorithmException e) {
   e.printStackTrace();
  }
  return "";
 }

 // 计算文件的 MD5 值
 public static String md5(File file) {
  if (file == null || !file.isFile() || !file.exists()) {
   return "";
  }
  FileInputStream in = null;
  String result = "";
  byte buffer[] = new byte[8192];
  int len;
  try {
   MessageDigest md5 = MessageDigest.getInstance("MD5");
   in = new FileInputStream(file);
   while ((len = in.read(buffer)) != -1) {
    md5.update(buffer, 0, len);
   }
   byte[] bytes = md5.digest();

   for (byte b : bytes) {
    String temp = Integer.toHexString(b & 0xff);
    if (temp.length() == 1) {
     temp = "0" + temp;
    }
    result += temp;
   }
  } catch (Exception e) {
   e.printStackTrace();
  }finally {
   if(null!=in){
    try {
     in.close();
    } catch (IOException e) {
     e.printStackTrace();
    }
   }
  }
  return result;
 }

 public static String md5(File file) {
  String result = "";
  FileInputStream in = null;
  try {
   in = new FileInputStream(file);
   MappedByteBuffer byteBuffer = in.getChannel().map(FileChannel.MapMode.READ_ONLY, 0, file.length());
   MessageDigest md5 = MessageDigest.getInstance("MD5");
   md5.update(byteBuffer);
   byte[] bytes = md5.digest();
   for (byte b : bytes) {
    String temp = Integer.toHexString(b & 0xff);
    if (temp.length() == 1) {
     temp = "0" + temp;
    }
    result += temp;
   }
  } catch (Exception e) {
   e.printStackTrace();
  } finally {
   if (null != in) {
    try {
     in.close();
    } catch (IOException e) {
     e.printStackTrace();
    }
   }
  }
  return result;
 }

 public static String md5(String string, int times) {
  if (TextUtils.isEmpty(string)) {
   return "";
  }
  String md5 = md5(string);
  for (int i = 0; i < times - 1; i++) {
   md5 = md5(md5);
  }
  return md5(md5);
 }

 public static String md5(String string, String slat) {
  if (TextUtils.isEmpty(string)) {
   return "";
  }
  MessageDigest md5 = null;
  try {
   md5 = MessageDigest.getInstance("MD5");
   byte[] bytes = md5.digest((string + slat).getBytes());
   String result = "";
   for (byte b : bytes) {
    String temp = Integer.toHexString(b & 0xff);
    if (temp.length() == 1) {
     temp = "0" + temp;
    }
    result += temp;
   }
   return result;
  } catch (NoSuchAlgorithmException e) {
   e.printStackTrace();
  }
  return "";
 }