Closing GZIPOutputStream after ByteStream copy in finally block break zip

Question

I have code which Zip and Unzip Text. I'm facing weird behavior - only when I close the GZIPOutputStream in certain place, the code works but when I try to place the GZIPOutputStream close in the finally block, it breaks and does not work. If you place the : gzipoutputstream.close() in the czip function where comment is placed, it will work. However if you keep it only in finally block, it will break. Why?

the ByteStreams.copy function is from com.google.common.io guava

public class Main {

    public static byte[] dzip(byte[] s) throws IOException {
        ByteArrayInputStream sStream = null;
        ByteArrayOutputStream oStream = null;
        InputStream gzipoutputStream = null;
        ByteBuffer arrReturn = null;
        try {
            sStream = new ByteArrayInputStream(s);
            oStream = new ByteArrayOutputStream();
            gzipoutputStream = new GZIPInputStream(sStream, 1024);
            ByteStreams.copy(gzipoutputStream, oStream);
            arrReturn = ByteBuffer.wrap(oStream.toByteArray());
        }
        catch (Exception e) {
            return null;
        } finally {
            if (gzipoutputStream != null) {
                gzipoutputStream.close();
            }
            if (oStream != null) {
                oStream.close();
            }
            if (sStream != null) {
                sStream.close();
            }

        }
        return arrReturn.array();
    }
    public static byte[] czip(byte[] s) throws IOException {

        ByteArrayInputStream sStream =null;
        ByteArrayOutputStream oStream =null;
        OutputStream gzipoutputstream = null;
        byte[] returnValue = null;

        try {
            sStream = new ByteArrayInputStream(s);
            oStream = new ByteArrayOutputStream(s.length / 2);
            gzipoutputstream = new GZIPOutputStream(oStream, 1024);
            ByteStreams.copy(sStream, gzipoutputstream);

            ////////////   ------------------------------------ \\\\\\\\\\\\
            //gzipoutputstream.close(); // < --- Works only when placed here
            ////////////   ------------------------------------   \\\\\\\\\\\\

            returnValue = oStream.toByteArray();  // Here the zip is 000

        }catch(Exception e) {
            return null;
        } finally {
            if (gzipoutputstream != null) {
                gzipoutputstream.close();
            }
            if (oStream != null) {
                oStream.close();
            }
            if (sStream != null) {
                sStream.close();
            }
        }
        return returnValue;
    }
    public static void main(String[] args) throws IOException {
        String s = "12313dsfafafafaf";
        byte[] source = (byte[]) s.getBytes();
        byte[] returnZipByteArr = czip(source);
        byte[] dd =  dzip(returnZipByteArr);
        String ss = new String(dd);
        System.out.println(ss);

    }
}

Have you given a try to `try-with-resources`? Didn't it work? — lealceldeiro, Apr 22 '19 at 06:49
I was asking if you tried using `try-with-resources` and how it went? — lealceldeiro, Apr 22 '19 at 07:47
I checked it, with `try-with-resources` it is the same. The problem is during dezipping zipped data. When `ByteStreams.copy` method is invoked there is exception being thrown - `java.io.EOFException: Unexpected end of ZLIB input stream` — Michał Krzywański, Apr 22 '19 at 07:59
You *must* close the `GZIPOutputStream` before executing `oStream.toByteArray()`. Otherwise it isn't finished and flushed. — user207421, Apr 22 '19 at 09:00

score 4 · Accepted Answer · answered Apr 22 '19 at 08:59

That's expected. The javadoc of close() says:

Writes remaining compressed data to the output stream and closes the underlying stream.

So if you try to access the bytes in the ByteArrayOutputStream() before close() has been called, the gzip compression hasn't been finished yet: the GZIP stream needs to know that nothing will never be written again to properly write the remaining data.

You could call finish() to have the same effect but without closing the stream (and thus still close it in the finally block).

Closing GZIPOutputStream after ByteStream copy in finally block break zip

1 Answers1