Bug ID 4813885 gère ce problème. Le commentaire de "DamonHD", soumis le 9 septembre 2006 (environ à mi-chemin du rapport de bug) contient un exemple de FlushableGZIPOutputStream qu'il a construit au-dessus de Jazzlib'snet.sf.jazzlib.DeflaterOutputStream.
Pour référence, voici un (reformaté) Extrait:
/**
* Substitute for GZIPOutputStream that maximises compression and has a usable
* flush(). This is also more careful about its output writes for efficiency,
* and indeed buffers them to minimise the number of write()s downstream which
* is especially useful where each write() has a cost such as an OS call, a disc
* write, or a network packet.
*/
public class FlushableGZIPOutputStream extends net.sf.jazzlib.DeflaterOutputStream {
private final CRC32 crc = new CRC32();
private final static int GZIP_MAGIC = 0x8b1f;
private final OutputStream os;
/** Set when input has arrived and not yet been compressed and flushed downstream. */
private boolean somethingWritten;
public FlushableGZIPOutputStream(final OutputStream os) throws IOException {
this(os, 8192);
}
public FlushableGZIPOutputStream(final OutputStream os, final int bufsize) throws IOException {
super(new FilterOutputStream(new BufferedOutputStream(os, bufsize)) {
/** Suppress inappropriate/inefficient flush()es by DeflaterOutputStream. */
@Override
public void flush() {
}
}, new net.sf.jazzlib.Deflater(net.sf.jazzlib.Deflater.BEST_COMPRESSION, true));
this.os = os;
writeHeader();
crc.reset();
}
public synchronized void write(byte[] buf, int off, int len) throws IOException {
somethingWritten = true;
super.write(buf, off, len);
crc.update(buf, off, len);
}
/**
* Flush any accumulated input downstream in compressed form. We overcome
* some bugs/misfeatures here so that:
* <ul>
* <li>We won't allow the GZIP header to be flushed on its own without real compressed
* data in the same write downstream.
* <li>We ensure that any accumulated uncompressed data really is forced through the
* compressor.
* <li>We prevent spurious empty compressed blocks being produced from successive
* flush()es with no intervening new data.
* </ul>
*/
@Override
public synchronized void flush() throws IOException {
if (!somethingWritten) { return; }
// We call this to get def.flush() called,
// but suppress the (usually premature) out.flush() called internally.
super.flush();
// Since super.flush() seems to fail to reliably force output,
// possibly due to over-cautious def.needsInput() guard following def.flush(),
// we try to force the issue here by bypassing the guard.
int len;
while((len = def.deflate(buf, 0, buf.length)) > 0) {
out.write(buf, 0, len);
}
// Really flush the stream below us...
os.flush();
// Further flush()es ignored until more input data data written.
somethingWritten = false;
}
public synchronized void close() throws IOException {
if (!def.finished()) {
def.finish();
do {
int len = def.deflate(buf, 0, buf.length);
if (len <= 0) {
break;
}
out.write(buf, 0, len);
} while (!def.finished());
}
// Write trailer
out.write(generateTrailer());
out.close();
}
// ...
}
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Je travaille avec Java6. – Hemeroc