A parallel HttpClient sendAync question

Daniel Fuchs daniel.fuchs at oracle.com
Tue Nov 13 11:05:21 UTC 2018

Hi Max,

On 13/11/2018 02:35, Weijun Wang 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 believe this is true.

> I can only collect the jobs into a list and then call join() on CompletableFuture.allOf(list). Is there a simpler way?

That's what I would use too. Though Chris Y.'s suggestion below
should also work:

On 13/11/2018 03:41, Chris Yin wrote: > lines.flapMap(x -> 
>     .map(l -> download(c, l))
>     .collect(Collectors.toList())
>     .forEach(f -> f.join());

since the collection should exhaust the stream before starting
the forEach loop.

best regards,

-- daniel

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