how to zip a folder itself using java

Have you tried Zeroturnaround Zip library? It's really neat! Zip a folder is just a one liner:

ZipUtil.pack(new File("D:\\reports\\january\\"), new File("D:\\reports\\january.zip"));

(thanks to Oleg Šelajev for the example)

Here is the Java 8+ example:

public static void pack(String sourceDirPath, String zipFilePath) throws IOException {
    Path p = Files.createFile(Paths.get(zipFilePath));
    try (ZipOutputStream zs = new ZipOutputStream(Files.newOutputStream(p))) {
        Path pp = Paths.get(sourceDirPath);
        Files.walk(pp)
          .filter(path -> !Files.isDirectory(path))
          .forEach(path -> {
              ZipEntry zipEntry = new ZipEntry(pp.relativize(path).toString());
              try {
                  zs.putNextEntry(zipEntry);
                  Files.copy(path, zs);
                  zs.closeEntry();
            } catch (IOException e) {
                System.err.println(e);
            }
          });
    }
}