使用可完成的期货处理实体清单

Question

I have a list of entities of type T . I also have a functional interface which acts as Supplier which has the method to performTask on entity and send back the result R which looks like:
R performTask(T entity) throws Exception .

I want to filter both: the successful results and errors & exceptions coming out of it onto separate maps. The code I wrote here is taking time, Kindly suggest what can be done.

I am looping on the list of entities, then process their completable future one by one, which I think is not the right way to do. Can you all suggest what can be done here ?

private void updateResultAndExceptionMaps(List < T > entities, final TaskProcessor < T, R > taskProcessor) {

 ExecutorService executor = createExecutorService();
 Map < T, R > outputMap = Collections.synchronizedMap(new HashMap < T, R > ());
 Map < T, Exception > errorMap = new ConcurrentHashMap < T, Exception > ();
 try {

  entities.stream()
   .forEach(entity -> CompletableFuture.supplyAsync(() -> {
     try {
      return taskProcessor.performTask(entity);
     } catch (Exception e) {
      errorMap.put(entity, (Exception) e.getCause());
      LOG.error("Error processing entity Exception: " + entity, e);
     }
     return null;
    }, executor)
    .exceptionally(throwable -> {
     errorMap.put(entity, (Exception) throwable);
     LOG.error("Error processing entity Throwable: " + entity, throwable);
     return null;
    })
    .thenAcceptAsync(R -> outputMap.put(entity, R))
    .join()
   ); // end of for-each 

  LOG.info("outputMap Map -> " + outputMap);
  LOG.info("errorMap Map -> " + errorMap);
 } catch (Exception ex) {
  LOG.warn("Error: " + ex, ex);
 } finally {
  executor.shutdown();
 }
}

outputmap should contain the entity and result, R .
errorMap should contain entity and Exception .

Answer 1

This is because you iterate over List of entities one by one, create CompletableFuture object and immediately block iteration because of join method which waits until given processor finishes it work or throw exception. You can do that with full multithreading support by converting each entity to CompletableFuture , collect all CompletableFuture instances and after that wait for all invoking join on each.

Below code should do the trick in your case:

entities.stream()
    .map(entity -> CompletableFuture.supplyAsync(() -> {
            try {
                return taskProcessor.performTask(entity);
            } catch (Exception e) {
                errorMap.put(entity, (Exception) e.getCause());
            }
            return null;
        }, executor)
                .exceptionally(throwable -> {
                    errorMap.put(entity, (Exception) throwable);
                    return null;
                })
                .thenAcceptAsync(R -> outputMap.put(entity, R))
    ).collect(Collectors.toList())
    .forEach(CompletableFuture::join);