How to use CompletableFuture to execute the threads parallaly without waiting and combine the result-CodePudding

I have executeGetCapability method which is executed in different threads but these threads runs sequentially..meaning one is completed after the other

    @Async("threadPoolCapabilitiesExecutor")
    public CompletableFuture<CapabilityDTO>  executeGetCapability(final String id, final LoggingContextData data){...}

and this method is called in following way:

public CapabilityResponseDTO getCapabilities(final List<String> ids) {
    final CapabilityResponseDTO responseDTO = new CapabilityResponseDTO();
    final List<CapabilityDTO> listOfCapabilityDTOS = new ArrayList<>();
    try {
        for (String id: ids) {
            listOfCapabilityDTOS .add(
                    asyncProcessService.executeGetCapability(id, LoggingContext.getLoggingContextData()).get());
        }
    } catch (Exception e) {
        ....
    }
    responseDTO.setDTOS(listOfCapabilityDTOS );
    return responseDTO;
}

How can i call executeGetCapability method using CompletableFuture so that thread runs in parallel without waiting for each other and then the result is combined ?? how can i use here CompletableFuture.supplyAsync and or .allOf methods ? Can someone explain me

Thanks

CodePudding user response：

The reduce helper function from this answer converts a CompletableFuture<Stream<T>> to a Stream<CompletableFuture<T>>. You can use it to asynchronously combine the results for multiple calls to executeGetCapability:

// For each id create a future to asynchronously execute executeGetCapability
Stream<CompletableFuture<CapabilityDTO>> futures = ids.stream()
    .map(id -> executeGetCapability(id, LoggingContext.getLoggingContextData()));

// Reduce the stream of futures to a future for a stream 
// and convert the stream to list
CompletableFuture<List<CapabilityDTO>> capabilitiesFuture = reduce(futures)
    .thenApply(Stream::toList);

responseDTO.setDTOS(capabilitiesFuture.get());

CodePudding user response：

This post was really helpful and answered my question. https://dzone.com/articles/java-8-parallel-processing-with-completable-future