Java - Create Zip file in memory

I find myself writing and rewriting this piece of code whenever I want to zip a set of files (in memory) and return the zipped file back as an object in memory. I often use this when the user requests a download of multiple reports and the deployment environment doesn't allow for disk access.

I thought I'd post it here so that I could copy-paste it the next time I need it :) If you've stumbled upon this page, you're free to use the code below too!

private static byte[] createZip(Map files) throws IOException {
    ByteArrayOutputStream bos = new ByteArrayOutputStream();
    ZipOutputStream zipfile = new ZipOutputStream(bos);
    Iterator i = files.keySet().iterator();
    String fileName = null;
    ZipEntry zipentry = null;
    while (i.hasNext()) {
        fileName = (String) i.next();
        zipentry = new ZipEntry(fileName);
        zipfile.putNextEntry(zipentry);
        zipfile.write((byte[]) files.get(fileName));
    }
    zipfile.close();
    return bos.toByteArray();
}