private AsyncTaskHandle<String> buildHandle() {
    String name = "ZipFileBuildTask: " + projectSlug + "-" + iterationSlug + "-" + localeId;
    AsyncTaskHandle<String> newHandle = new AsyncTaskHandle<String>(name);

    // Max documents to process
    DocumentDAO documentDAO = (DocumentDAO) Component.getInstance(DocumentDAO.class);
    final List<HDocument> allIterationDocs =
        documentDAO.getAllByProjectIteration(projectSlug, iterationSlug);
    newHandle.setMaxProgress(allIterationDocs.size() + 1); // all files plus
    // the zanata.xml
    // file

    return newHandle;
  }
  @Override
  public String call() throws Exception {
    // Needed Components
    DocumentDAO documentDAO = (DocumentDAO) Component.getInstance(DocumentDAO.class);
    LocaleDAO localeDAO = (LocaleDAO) Component.getInstance(LocaleDAO.class);
    ResourceUtils resourceUtils = (ResourceUtils) Component.getInstance(ResourceUtils.class);
    TextFlowTargetDAO textFlowTargetDAO =
        (TextFlowTargetDAO) Component.getInstance(TextFlowTargetDAO.class);
    FileSystemService fileSystemService =
        (FileSystemService) Component.getInstance(FileSystemServiceImpl.class);
    ConfigurationService configurationService =
        (ConfigurationService) Component.getInstance(ConfigurationServiceImpl.class);

    final String projectDirectory = projectSlug + "-" + iterationSlug + "/";
    final HLocale hLocale = localeDAO.findByLocaleId(new LocaleId(localeId));
    final String mappedLocale = hLocale.getLocaleId().getId();
    final String localeDirectory = projectDirectory + mappedLocale + "/";

    final File downloadFile = fileSystemService.createDownloadStagingFile("zip");
    final FileOutputStream output = new FileOutputStream(downloadFile);
    final ZipOutputStream zipOutput = new ZipOutputStream(output);
    zipOutput.setMethod(ZipOutputStream.DEFLATED);
    final PoWriter2 poWriter = new PoWriter2(false, !isPoProject);
    final Set<String> extensions = new HashSet<String>();

    extensions.add("gettext");
    extensions.add("comment");

    // Generate the download descriptor file
    String downloadId =
        fileSystemService.createDownloadDescriptorFile(
            downloadFile, projectSlug + "_" + iterationSlug + "_" + localeId + ".zip", userName);

    // Add the config file at the root of the project directory
    String configFilename = projectDirectory + configurationService.getConfigurationFileName();
    zipOutput.putNextEntry(new ZipEntry(configFilename));
    zipOutput.write(
        configurationService
            .getConfigForOfflineTranslation(projectSlug, iterationSlug, hLocale)
            .getBytes());
    zipOutput.closeEntry();
    getHandle().increaseProgress(1);

    final List<HDocument> allIterationDocs =
        documentDAO.getAllByProjectIteration(projectSlug, iterationSlug);
    for (HDocument document : allIterationDocs) {
      // Stop the process if signaled to do so
      if (getHandle().isCancelled()) {
        zipOutput.close();
        downloadFile.delete();
        fileSystemService.deleteDownloadDescriptorFile(downloadId);
        return null;
      }

      TranslationsResource translationResource = new TranslationsResource();
      List<HTextFlowTarget> hTargets = textFlowTargetDAO.findTranslations(document, hLocale);
      resourceUtils.transferToTranslationsResource(
          translationResource, document, hLocale, extensions, hTargets, Optional.<String>absent());

      Resource res = resourceUtils.buildResource(document);

      String filename = localeDirectory + document.getDocId() + ".po";
      zipOutput.putNextEntry(new ZipEntry(filename));
      poWriter.writePo(zipOutput, "UTF-8", res, translationResource);
      zipOutput.closeEntry();

      getHandle().increaseProgress(1);
    }

    zipOutput.flush();
    zipOutput.close();

    return downloadId;
  }