GZIPInputStream format issues

Question

I'm having trouble reading through a GZipped BlueCoat log file. The first six lines of the file are a header, and these lines can be read perfectly, but none of the following content.

I have tried unzipping the log manually, and then trying to read the file with slightly modified code, and that works okay. I suspect this is an issue with ASCII versus UTF8 versus UTF16 but I cannot get to the bottom of this, especially since it seems to change mid-file.

Code I have at the moment is:

InputStream fileStream;
InputStream gzipStream;
Reader decoder;
BufferedReader thisBr;

try {
    fileStream  = new FileInputStream(currentFile);
    gzipStream  = new GZIPInputStream(fileStream);
    decoder     = new InputStreamReader(gzipStream, "UTF-8");
    thisBr      = new BufferedReader(decoder);                    

    String logLine = thisBr.readLine();
    while (logLine != null)
    {
        logWriter.write(logLine + "\n");
        logLine = thisBr.readLine();
    }
    logWriter.flush();
    gzipStream.close();
} catch (IOException e) {
    System.out.println("Exception has been thrown:" + e);
}