Zipping InputStream, returning InputStream (in memory, no file)

Question

I am trying to do compress an InputStream and return an InputStream:

public InputStream compress (InputStream in){
  // Read "in" and write to ZipOutputStream
  // Convert ZipOutputStream into InputStream and return
}

I am compressing one file (so I could use GZIP) but will do more in future (so I opted for ZIP). In most of the places:

Compress an InputStream with gzip
How can I convert ZipInputStream to InputStream?

They use toBytesArray() or getBytes() which do not exist (!) - ZipOutputStream

My problems are:

How do I convert the ZipOutPutStream into InputStream if such methods don't exist?
When creating the ZipOutPutStream() there is no default constructor. Should I create a new ZipOutputStrem(new OutputStream() ) ??

[This](http://www.javaworld.com/community/node/8362) should help. — Boris the Spider, Jul 29 '13 at 15:33
Thanks Boris the Spider, but that only shows operation with ZIP files, which I know. I am missing some basic Java I/O I think, not how to compress them — user1156544, Jul 29 '13 at 15:36

score 11 · Answer 1 · edited May 16 '17 at 16:10

11

Something like that:

private InputStream compress(InputStream in, String entryName) throws IOException {
        final int BUFFER = 2048;
        byte buffer[] = new byte[BUFFER];
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        ZipOutputStream zos = new ZipOutputStream(out);
        zos.putNextEntry(new ZipEntry(entryName));
        int length;
        while ((length = in.read(buffer)) >= 0) {
            zos.write(buffer, 0, length);
        }
        zos.closeEntry();
        zos.close();
        return new ByteArrayInputStream(out.toByteArray());
}

edited May 16 '17 at 16:10

Zefiro

2,821
2
20
21

answered Aug 08 '13 at 11:07

soda

111
3

3

Just a small note: In the while statement, you should check if in.read(buffer) >= 0. Because if the inputstream isn't ready, it might return 0 bytes read, but the end isn't reached, the stream might be ready later. So it shouldn't be considered finished until it returns -1 – Einar Bjerve Jun 03 '16 at 13:29
1

Is it possible to do the same using GZIP? – Dinesh Nov 29 '19 at 10:21

score 2 · Accepted Answer · answered Jul 30 '13 at 12:32

2

Solved it with a ByteArrayOutputStream which has a .toByteArray()
Same here, passing the aforementioned element

answered Jul 30 '13 at 12:32

user1156544

1,725
2
25
51

Zipping InputStream, returning InputStream (in memory, no file)

2 Answers2