Question

We are processing a byte[] as shown below (the file is POST’ed to a web server, this code is running in Glassfish) and have found that some files have a byte-order mark (BOM, a three-byte sequence 0xEF,0xBB,0xBF, see: http://en.wikipedia.org/wiki/Byte_order_mark) at the beginning, and we want to remove this BOM. How would we detect and remove a BOM in this code? Thanks.

  private final void serializePayloadToFile(File file, byte[] payload) throws IOException {

    FileOutputStream fos;
    DataOutputStream dos;

    fos = new FileOutputStream(file, true); // true for append
    dos = new DataOutputStream(fos);

    dos.write(payload);
    dos.flush();
    dos.close();
    fos.close();

    return;
  }  

Answer 1

How would we detect […]

There’s obviously no way to tell for sure if the three bytes are three random bytes or three bytes representing a BOM.

You could check if the array starts with 0xEF, 0xBB, 0xBF and in that case skip them.

[…] and remove a BOM in this code?

Something like this should do:

int off = payload.length >= 3
       && payload[0] == 0xEF
       && payload[1] == 0xBB
       && payload[2] == 0xBF ? 3 : 0

dos.write(payload, off, payload.length - off);