Qfyilyi

guys! I have a question: what does this code do:

Collection<Contract.class> contracts = fillTheCollectionFromDb();

contracts.stream().filter(condition)

                  .map(contractItem ->

                       CompletableFuture.supplyAsync(() -> 

                           {T result = getAnotherDataFromDb(contractItem); 

                            return result;}, Executor.class)

                  )//end .map

                  .map(CompletableFuture::join).collect(Collectors.toList());

this code is equivalent to:

Collection<Contract> contracts = fillTheCollectionFromDb();

contracts.stream().filter(condition)

              .map(this::getAnotherDataFromDb)

              .collect(Collectors.toList());

To make this program truly parallel, it should be modified. First, launch all the requests to database in parallel:

Collection<Contract> contracts = fillTheCollectionFromDb();

List<CompletableFuture> futures = contracts.stream().filter(condition)

              .map(contractItem ->

                   CompletableFuture.supplyAsync(

                         ()->getAnotherDataFromDb(contractItem),

                       executor)

              )//end .map

              .collect(Collectors.toList());

and only after that collect all the results:

List results = futures.stream

      .map(CompletableFuture::join)

      .collect(Collectors.toList());