监控GZip下载Java的进展

Question

I download some files in my java app and implemented a download monitor dialog. But recently I compressed all the files with gzip and now the download monitor is kind of broken.

I open the file as a GZIPInputStream and update the download status after every kB downloaded. If the file has a size of 1MB the progress goes up to eg 4MB which is the uncompressed size. I want to monitor the compressed download progress. Is this possible?

EDIT: To clarify: I'm reading the bytes from the GZipInputStream which are the uncompressed bytes. So that does not give me the right filesize at the end.

Here is my code:

URL url = new URL(urlString);
HttpURLConnection con = (HttpURLConnection) url.openConnection();
con.connect();
...
File file = new File("bibles/" + name + ".xml");
if(!file.exists())
    file.createNewFile();
out = new FileOutputStream(file);
in = new BufferedInputStream(new GZIPInputStream(con.getInputStream()));

byte[] buffer = new byte[1024];
int count;
while((count = in.read(buffer)) != -1) {
    out.write(buffer, 0, count);
    downloaded += count;
    this.stateChanged();
}

...

private void stateChanged() {
    this.setChanged();
    this.notifyObservers();
}

Thanks for any help!

Answer 1

According to the specification, GZIPInputStream is a subclass of InflaterInputStream . InflaterInputStream has a protected Inflater inf field that is the Inflater used for the decompression work. Inflater.getBytesRead should be particularly useful for your purposes.

Unfortunately, GZIPInputStream does not expose inf , so probably you'll have to create your own subclass and expose the Inflater , eg

public final class ExposedGZIPInputStream extends GZIPInputStream {

  public ExposedGZIPInputStream(final InputStream stream) {
    super(stream);
  }

  public ExposedGZIPInputStream(final InputStream stream, final int n) {
    super(stream, n);
  }

  public Inflater inflater() {
    return super.inf;
  }
}
...
final ExposedGZIPInputStream gzip = new ExposedGZIPInputStream(...);
...
final Inflater inflater = gzip.inflater();
final long read = inflater.getBytesRead();