How can we pass play.libs.concurrent.HttpExecutionContext to parallel stream in Java 8?

user_6106147 0
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In a play framework project controller, I was processing a list of objects using forEach() which was working fine. 

List<Post> posts = repository.getPosts();
posts.forEach(post -> {
    //...some processing

    anyFunc(); //<-- internally uses HttpExecutionContext

    //...further processing
});

But when I tried to process these list of objects parallelly using parallelStream() to improve the performance, I lost instance of HttpExecutionContext inside parallel stream.

List<Post> posts = repository.getPosts();
posts.parallelStream().forEach(post -> {
    //...some processing

    anyFunc(); //<-- not able to use HttpExecutionContext now

    //...further processing
});

I cannot pass HttpExecutionContext as argument to anyFunc. Is there any way in which I can pass/set HttpExecutionContext in parallelStream()?

playframework stream java
1 Answers

Use HttpExecutionContext.execute 

public class HomeController extends Controller {
    @Inject HttpExecutionContext ec;

    public Result index() {
        // The data to parallel processing
        List<String> list = List.of("Item 1", "Item 2", "Item 3","Item 4", "Item 5", "Item 6", "Item 7", "Item 8");

        // Make a Stream. The `parallelStream` is not used because 
        // `current.execute` will make it run in parallel.
        Stream<String> listInParralel = list.stream(); 

        // The current executor with the HTTP context. 
        Executor current = ec.current();

        System.out.println("START");
        listInParralel.forEach(item -> {
          current.execute(()-> {
            // request().uri() internally uses HttpExecutionContext
            System.out.println("item: " + item + " in "  +  request().uri()  + "(" + Thread.currentThread().getName() + ")");
          });
        });

        // Results
        /*
        START
        item: Item 7 in /(application-akka.actor.default-dispatcher-9)
        item: Item 5 in /(application-akka.actor.default-dispatcher-7)
        item: Item 3 in /(application-akka.actor.default-dispatcher-5)
        item: Item 1 in /(application-akka.actor.default-dispatcher-6)
        item: Item 6 in /(application-akka.actor.default-dispatcher-8)
        item: Item 4 in /(application-akka.actor.default-dispatcher-2)
        item: Item 2 in /(application-akka.actor.default-dispatcher-4)
        item: Item 8 in /(application-akka.actor.default-dispatcher-9)
        */

        return ok("Done");
    }

}

Still, I prefer to cache the HTTP data and then use them in parallel processing. Do not like to bother with HttpExecutionContext:

public class HomeController extends Controller {
    @Inject HttpExecutionContext ec;

    public Result index() {
        // The data to parallel processing
        List<String> list = List.of("Item 1", "Item 2", "Item 3","Item 4", "Item 5", "Item 6", "Item 7", "Item 8");
        Stream<String> listInParralel = list.parallelStream(); 

        // Take all that you need from the HttpExecutionContext.  
        String uri = request().uri();

        System.out.println("START");
        listInParralel.forEach(item -> {
            // use pre cached HTTP context data, liek `uri`
            System.out.println("item: " + item + " in "  +  uri  + "(" + Thread.currentThread().getName() + ")");
        });

        // Results
        /*
        START
        item: Item 1 in /(ForkJoinPool.commonPool-worker-7)
        item: Item 8 in /(ForkJoinPool.commonPool-worker-3)
        item: Item 7 in /(ForkJoinPool.commonPool-worker-15)
        item: Item 4 in /(ForkJoinPool.commonPool-worker-9)
        item: Item 3 in /(ForkJoinPool.commonPool-worker-13)
        item: Item 2 in /(ForkJoinPool.commonPool-worker-5)
        item: Item 5 in /(ForkJoinPool.commonPool-worker-11)
        item: Item 6 in /(application-akka.actor.default-dispatcher-4)
        */

        return ok("Done");
    }

}
user_11184190
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