Question

Given ZipFile zip, its ZipEntry entry and target File unzippedEntryFile, what is the most readable way to write entry to unzippedEntryFile?

I came up with following solution using Google Guava and Apache.Commons.IO:

InputSupplier<ByteArrayInputStream> entryInputSupplier = ByteStreams.newInputStreamSupplier(IOUtils.toByteArray(zip.getInputStream(entry)));
Files.copy(entryInputSupplier, unzippedEntryFile);

However, something tells me it can be made simplier.

Thanks,
Konrad

Answer 1

I don’t know what’s not readable about your code, other than that you have a lot of nested calls. These can be broken out and assigned to local variables, which would make the code longer (but, in my opinion, a bit more readable).

You do seem to be processing the data twice — once to read it into a byte array and again to copy it to the file. I haven’t tested this, but it should work and cut the amount of data movement in half:

final InputStream zipStream = zip.getInputStream(entry);
InputSupplier<InputStream> supplier = new InputSupplier<InputStream>() {
    InputStream getInput() {
        return zipStream;
    }
};
Files.copy(supplier, unzippedEntryFile);

You could, in fact, create your own little class that implements InputSuppler<InputStream>. I’m surprised that I couldn’t find one in the Guava library. (Apparently, others have been surprised at this as well.)