Task Executor 与 Java 8 并行流

Question

I can't find a specific answer to the line of investigation that we've been requested to take on

I see that parallel streams may not be so performant when using small amount of threads, and that apparently it doesn't behave so well when the DB blocks the next request while processing the current one

However, I find that the overhead of implementing Task Executor vs Parallel Streams is huge, we've implemented a POC that takes care of our concurrency needs with just this one line of code:

List<Map<String, String>> listWithAllMaps = mappedValues.entrySet().parallelStream().map(e -> callPlugins(e))
        .collect(Collectors.toList());

Whereas in Task Executor, we'd need to override the Runnable interface and write some cumbersome code just to get the runnables not to be void and return the values we're reading from the DB, leading us into several hours, if not days of coding, and producing a less maintainable, more bug prone code

However, our CTO is still reluctant to using parallel streams due to unforeseen issues that could come up down the road

So the question is, in an environment where I need to make several concurrent read-only queries to a database, using different java-components/REST calls for each query: Is it preferrable in any way to use Task Executor instead of parallel streaming, if so, why?

Answer 1

Use the TaskExecutor as an Executor for a CompletableFuture .

List<CompletableFuture> futures = mappedValues.entrySet().stream().map(e - > CompletableFuture.supplyAsync(() -> callPlugins(e), taskExecutor)).collect(Collectors.toList());

List<Map<String, String>> listWithAllMaps = futures.stream().map(CompletableFuture::join).collect(Collectors.toList());

Not sure how this is cumbersome. Yes it is a bit more code, but with the advantage that you can easily configure the TaskExecutor and increase the number of threads, queueu-size etc. etc.

DISCLAIMER: Typed it from the top of my head, so some minor things might be of with the code snippet.