// want to parallelize this for loop
  for (Task task : tasks) {
    if (task.getCategories().isEmpty() || task.getEventList() == null
        || task.getMetaInfo() == null) {
      continue;
    }
    String itemId = task.getEventList().getId();
    String categoryId = task.getCategories().get(0).getId();
    Processor fp = new Processor(siteId, itemId, categoryId, poolType);
    Map<String, Integer> holder = fp.getDataHolder();
    if (!holder.isEmpty()) {
      for (Map.Entry<String, Integer> entry : holder.entrySet()) {
        info.putIfAbsent(entry.getKey(), entry.getValue());
      }
      List<Integer> values = new ArrayList<>();
      for (String key : holder.keySet()) {
        values.add(info.get(key));
      }
      itemToNumberMapping.put(itemId, StringUtils.join(values, ","));
      catToValueHolder.put(categoryId, StringUtils.join(values, ","));
    }
    Category cat = getCategory(task, holder.isEmpty());
    dealsByLeafCategory.add(cat);
    LinkedList<String> ids = getCategoryIds(task);
    catHolder.put(categoryId, ids.getLast());
    itemIds.add(itemId);
  }

private final ExecutorService service = Executors.newFixedThreadPool(10);

List<Future<Output>> futures = new ArrayList<Future<Output>>();
for (final Input input : inputs) {
  Callable<Output> callable = new Callable<Output>() {
    public Output call() throws Exception {
      Output output = new Output();
      // process your input here and compute the output
      return output;
    }
  };
  futures.add(service.submit(callable));
}

service.shutdown();

List<Output> outputs = new ArrayList<Output>();
for (Future<Output> future : futures) {
  outputs.add(future.get());
}