🚀 go-pugleaf

I'm trying to create a bitmap file using the data in an old .rc file.  For
example, the input data looks as follows:
BOXIN BITMAP LOADONCALL MOVEABLE DISCARDABLE
{
 '42 4D 56 02 00 00 00 00 00 00 76 00 00 00 28 00'
 '00 00 1E 00 00 00 1E 00 00 00 01 00 04 00 00 00'
 '00 00 E0 01 00 00 00 00 00 00 00 00 00 00 00 00'
 '00 00 00 00 00 00 00 00 00 00 00 00 80 00 00 80'
 '00 00 00 80 80 00 80 00 00 00 80 00 80 00 80 80'
}
 I'm using the following to create the binary file:
  FileReader filereader = new FileReader(rcfile);
  LineNumberReader linereader = new LineNumberReader(filereader);

  FileOutputStream out = new FileOutputStream(file);
  OutputStreamWriter outwriter = new OutputStreamWriter(out);

   String nextLine = linereader.readLine().trim();
   while (nextLine.charAt(0) != '}') {
           StringTokenizer tokenizer = new StringTokenizer(nextLine, "' ");
           while (tokenizer.hasMoreTokens()) {
               String token = tokenizer.nextToken();

               int hexdata = Integer.parseInt(token, 16);
               outwriter.write(hexdata);
            }
            nextLine = linereader.readLine().trim();
   }
    outwriter.close();

The problem that I'm having is with the '80' values in the resource file.
It seems that 'outwriter.write(hexdata)' writes out 0x3F to the output file
rather than 0x80.
I suspect the heart of the problem lies with the fact that bytes are signed
in Java.

But I don't know the right way of doing this.
Can anyone suggest how this should be done?
Thanks.