public class ZipFiles {

    private static final String sourceDir = "D:\\test\\";
    private static final String targetDir = "D:\\test_archive\\";
    private static Map<String,ZipOutputStream> zosMap = null;

    private static void zipFile(String fileName) throws FileNotFoundException, IOException {
        File fl = new File(sourceDir + fileName);

        Date fileDate = new Date(fl.lastModified());
        SimpleDateFormat dateFormat = new SimpleDateFormat("yyyyMMdd");
        String zipFileName = dateFormat.format(fileDate) + ".zip";
        String dateFormatString = dateFormat.format(fileDate);

        ZipOutputStream zout = null;
        //ZipOutputStream zout = new ZipOutputStream(new FileOutputStream(targetDir + zipFileName));
        if (zosMap.containsKey(dateFormatString)){
            zout = zosMap.get(dateFormatString);
        } else {
            zosMap.put(dateFormatString,new ZipOutputStream(new FileOutputStream(targetDir + zipFileName)));
        }
        FileInputStream fis = null;
        try {
            fis = new FileInputStream(sourceDir + fileName);
            ZipEntry entry = new ZipEntry(fileName);
            zout.putNextEntry(entry);

            byte[] buffer = new byte[fis.available()];
            fis.read(buffer);
            // вроде как добавляем содержимое к архиву
            zout.write(buffer);
            fl.delete();
        } catch (Exception ex) {
            System.out.println(ex.getMessage());
        } finally {
            // zout.closeEntry();
            fis.close();
        }
    }

    public static void main(String[] args) throws Exception {
        zosMap = new HashMap<>();
        try (DirectoryStream<Path> stream = Files.newDirectoryStream(Paths.get(sourceDir))) {
            for (Path file : stream)
                if (!file.toFile().isDirectory() && file.getFileName().toString().endsWith(".xml"))
                    zipFile(file.getFileName().toString());
            for(Map.Entry<String,ZipOutputStream> zentry : zosMap.entrySet()){
                zentry.getValue().close();
            }
        } catch (IOException | DirectoryIteratorException x) {
            System.err.println(x);
        }
    }
}