[FIXED] How can I consolidate each thread result - java

Issue

I want execute some java logic with multiple threads and that method return a List. So finally I want all threads result into single List? Is it possible with Java ExecutorService or Multithreading ? or any other java frameworks ?

Solution

There are different ways to do it, here is my suggestion:

Create a list of Callable (see more about it in the docs):

List<Callable<Object>> callables = new ArrayList<>();

Add your tasks to this list:

callables.add(() -> {
            // do something
        });

Then invoke those Callables by passing them to the invokeAll() method of ExecutorService and receive a List of Future<Object>. For example:

ExecutorService executor = Executors.newFixedThreadPool(5);
List<Future<Object>> results = executor.invokeAll(callables);

You can then get each of the thread results by getting them via index call from the result list - in the same order as which you passed them to your Callable list.

So, to get the result of the first thread that you passed to the Callable list, simply do:

  CastedResult result = (CastedResult) results.get(0).get(); 

Finally, you can collect all results in a single list as you wish.

Also, this is a helpful article on how to use ExecutorService (and remember to shutdown the Executor after you finish working with it, as explained here).

Answered By - Petar Bivolarski