A question about encrypting file using AES

my code is:

-----------------------------------------------------
  public static boolean enDeCrypt(String keyStr, File fin, File fout) {
    try {
     FileInputStream in = new FileInputStream(fin);
      FileOutputStream out = new FileOutputStream(fout);
      Cipher desCipher = Cipher.getInstance("AES");
      desCipher.init(Cipher.ENCRYPT_MODE,
                            new SecretKeySpec(keyStr.getBytes("UTF-8"),
"AES"));
      CipherOutputStream cos = new CipherOutputStream(out, desCipher);
      byte[] enBuffer = new byte[4096];
      int n;
      while ( (n = in.read(enBuffer)) != -1) {
        cos.write(enBuffer, 0, n);
      }
      cos.close();
    }
    catch (Exception e) {
      e.printStackTrace();
      return false;
    }
    return true;
  }
-----------------------------------------------------

but it throw exception:
java.security.InvalidKeyException: Illegal key size or default
parameters
I used a 192-bit key

if I change the key's length, it will throw excepion:
java.security.InvalidKeyException: Invalid AES key length: 272
It seemed that it is not the problem about the length of the key

how can I fix it

Thank you very much in advance