A parallel HttpClient sendAync question

[Chris Yin]

> On 13 Nov 2018, at 10:35 AM, Weijun Wang <weijun.wang at oracle.com> wrote:
> 
> I'm scanning a file and downloading links inside:
> 
> lines.flapMap(x -> Stream.ofNullable(findURIFrom(x)))
>     .map(l -> download(c, l))
>     .forEach(f -> f.join());
> 
> CompletableFuture<HttpResponse<Path>> download(HttpClient c, URI link) {
>    return c.sendAsync(HttpRequest.newBuilder(link).build(),
>            HttpResponse.BodyHandlers.ofFile(Path.of(link.getPath())));
> }
> 
> However, it seems the download is one by one and not parallel. I guess maybe map() is lazy and each request is only send when forEach() is called and the next one is only sent after join().
> 
> I can only collect the jobs into a list and then call join() on CompletableFuture.allOf(list). Is there a simpler way?

Just guess your Stream (lines) is not parallel, so either use parallel stream or collect into list before join should work?

lines.parallel().flapMap(x -> Stream.ofNullable(findURIFrom(x)))
    .map(l -> download(c, l))
    .forEach(f -> f.join());

Or

lines.flapMap(x -> Stream.ofNullable(findURIFrom(x)))
    .map(l -> download(c, l))
    .collect(Collectors.toList())
    .forEach(f -> f.join());

Regards,
Chris

> 
> Thanks
> Max