I would like to create a zip archive from a folder and keep entries for (non-empty) directories.

In the code below, FileInputStream throws a FileNotFoundException when a directory is passed to AddToZip. I have tried to put a condition around the actual writing of bytes but it makes the whole archive invalid. How can I add directory entries to the archive?

public static void addToZip(File directoryToZip, File file, ZipOutputStream zos) throws FileNotFoundException,
        IOException {

    String zipFilePath = file.getCanonicalPath().substring(directoryToZip.getCanonicalPath().length() + 1,file.getCanonicalPath().length());
    System.out.println("Writing '" + zipFilePath + "' to zip file");
    ZipEntry zipEntry = new ZipEntry(zipFilePath);
    zos.putNextEntry(zipEntry);
    FileInputStream fis = new FileInputStream(file); // Throws a FileNotFoundException when directory
    byte[] bytes = new byte[1024];
    int length;
    while ((length = fis.read(bytes)) >= 0) {
        zos.write(bytes, 0, length);
    }

    zos.closeEntry();
    fis.close();

}