Java http download corrupts file

Question

Hello all!

I have a problem, which I do not seem to be able to solve... I do a http download of a file, but the CRC32 of the file on the server and on the client do not match. Also, the file has different size, so obviously I must be doing something wrong... when I download via Firefox, the filesize is ok... so I guess it is somewhere in the client code.

I already found http://stackoverflow.com/questions/401748/corrupt-file-when-using-java-to-download-file, but that didn't help me either...

Here's the code:

private void downloadJar(String fileName, long crc32Server) throws IOException {
  System.out.println("Downloading file '" + fileName + "' from server '" + mServer + "'.");
  HttpURLConnection sourceConnection = null;
  BufferedInputStream inputStream = null;
  BufferedWriter fileWriter = null;
  long crc32Client;
  try {
    URL sourceURL = new URL(fileName);
    try {
      sourceConnection = (HttpURLConnection)sourceURL.openConnection();
    }
    catch (MalformedURLException exc) {
      throw new RuntimeException("Configured URL caused a MalformedURLException: ", exc);
    }
    sourceConnection.setRequestProperty("Accept-Encoding", "zip, jar");
    sourceConnection.connect();
    inputStream = new BufferedInputStream(sourceConnection.getInputStream());
    fileWriter = new BufferedWriter(new FileWriter(targetFolder + File.separator + fileName));
    CRC32 crc32 = new CRC32();
    for (int singleByte = inputStream.read(); singleByte != -1; singleByte = inputStream.read()) {
      fileWriter.write(singleByte);
      crc32.update(singleByte);
    }
    crc32Client = crc32.getValue();
  }
  finally {
    if (inputStream != null) {
      inputStream.close();
    }
    if (fileWriter != null) {
      fileWriter.flush();
      fileWriter.close();
    }
    if (sourceConnection != null) {
      sourceConnection.disconnect();
    }
  }
  if (crc32Client != crc32Server) {
    //      deleteFile(fileName);
    throw new IOException("CRC32 did not match for file '" + fileName + "': " + crc32Client + "!="
        + crc32Server);
  }
}

Answer 1

You should use a BufferedOutputStream instead of a FileWriter/BufferedWriter. In general, *Streams handle raw binary data, while *Writers handle character data (which is an interpretation of the raw binary data for a given character encoding).