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Java 8 parallel stream of list of method param

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无人共我
无人共我 2021-01-15 09:09

I have a method:

invokList(List list);



This method is inside a jar and I have no access to the source code of it. So for that         


        
      
      
      

        

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                   暗喜
                                             
                
                
                (楼主)
            
              
                  
    
                2021-01-15 09:25
              
    

            
    
            
    
              
              

    Looks very verbose, but you can try the following. The runAsync() method will make the list chunks run in parallel.
    


    private void test(List list, int chunkSize) throws ExecutionException, InterruptedException {
    AtomicInteger prev = new AtomicInteger(0);
    List futures = new ArrayList<>();
    IntStream.range(1, (int) (chunkSize * (Math.ceil(Math.abs(list.size() / (double) chunkSize)))))
            .filter(i -> i % chunkSize == 0 || i == list.size())
            .forEach(i -> {
                List chunk = list.subList(prev.get(), i);
                futures.add(CompletableFuture.runAsync(() -> invokeList(chunk)));
                prev.set(i);
            });
    CompletableFuture.allOf(futures.toArray(new CompletableFuture[0])).get();
}

private void invokeList(List list) {
    System.out.println("Invoked for: " + list);
}



    I ran it for a list of 30 integers, with a chunk size of 5 like this:
    


    public static void main(String[] args) throws ExecutionException, InterruptedException {
    List list = IntStream.range(0, 30).mapToObj(i1 -> (Object) String.valueOf(i1)).collect(Collectors.toList());
    int chunkSize = 5;
    new Test().test(list, chunkSize);
}



    Output:
    


    Invoked for: [15, 16, 17, 18, 19]
Invoked for: [0, 1, 2, 3, 4]
Invoked for: [5, 6, 7, 8, 9]
Invoked for: [10, 11, 12, 13, 14]
Invoked for: [20, 21, 22, 23, 24]

    
    
    
             
    
                                                        
    
            
            
    
              
                
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