Writing zipped byte[] into file

Question

I am trying to write a zipfile to a byte[] in memory, and then write that out to disk. The resulting zipfile is corrupt.

This works:

try (FileOutputStream fos = new FileOutputStream(Files.createTempFile("works", ".zip").toFile());
     ZipOutputStream zos = new ZipOutputStream(fos)) {
    zos.putNextEntry(new ZipEntry("test.txt"));
    zos.write("hello world".getBytes());
    zos.closeEntry();
}

This is broken and creates a corrupt zip file:

try (ByteArrayOutputStream bos = new ByteArrayOutputStream();
     ZipOutputStream zos = new ZipOutputStream(bos)) {
    zos.putNextEntry(new ZipEntry("test.txt"));
    zos.write("hello world".getBytes());
    zos.closeEntry();

    Files.write(Files.createTempFile("broken", ".zip"), bos.toByteArray());
}

Why would the second one not work? And how can I fix it, assuming that I need to operate on a raw byte[] (I can't create the zip file directly into a file, since I need the byte[] for other purposes).

There is a more suitable format for single file compression: `test.txt.gz` using a **GZipOutputStream**. — Joop Eggen, May 06 '15 at 14:51
Close `ZipOutputStream` and `FileOutputStream ` after `zos.closeEntry();`. — LittlePanda, May 06 '15 at 14:54
Why? Why not just write it direct to disk and save all that time and space? — user207421, May 07 '15 at 02:03
@EJP as I noted in the question, I need the `byte[]` for other purposes — Yosef Weiner, May 15 '15 at 04:21

Kayaman · Accepted Answer · 2015-05-06T14:53:47.483

4

You might want to flush zos before writing bos, since it won't be closed until after the try-with-resources (and therefore zos is not necessarily flushed through to bos yet when you're writing the bytes to file).

Edit: you need to call zos.finish(); to...well finish the compression. The close() method will call it normally.

edited May 06 '15 at 14:53

answered May 06 '15 at 14:50

Kayaman

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Doesn't help, still corrupt – Yosef Weiner May 06 '15 at 14:51
How does the corrupt file differ from the intact one? – Kayaman May 06 '15 at 14:51
1

I would compare the sizes first, but see my edit about `finish()`. – Kayaman May 06 '15 at 14:55

Writing zipped byte[] into file

1 Answers1