如何异步调用一个方法并运行它？

Question

有没有办法在 Java 8 中仅从 main() 异步运行 getUsers()?

运行 getUsers() 在主线程上需要 300 秒。我希望用 4 个核心在 180 秒内完成。

public class Main {

  // Getting users (with sleep)
  public List<User> getUsers() {

    
    List<User> users = new ArrayList();
    for(int i = 0; i < 100; i++) {
      users.add(new User("someName", "someAge"));
      TimeUnit.MILLISECONDS.sleep(3000);
    }
    return users;
  }

  public static void main(String[] args) {
    
    List<User> users = getUsers();
  }  
}

在不修改 getUsers()（objective）的情况下，运行以下内容仍需要 300 秒：

  public static void main(String[] args) {
    
    List<User> users =
    CompletableFuture.supplyAsync(() -> getUsers()).join();
  }

Answer 1

您可以将用户创建循环分成更小的循环，然后运行它们并行进行。考虑这个例子，运行s 快 4 倍：

public static void main(String[] args) {
    // create a pool executor of 4 threads, increase or decrease it if need
    Executor executor = Executors.newFixedThreadPool(4); 

    CompletableFuture<List<User>> future1 = CompletableFuture.supplyAsync(() -> getUsers(25), executor);
    CompletableFuture<List<User>> future2 = CompletableFuture.supplyAsync(() -> getUsers(25), executor);
    CompletableFuture<List<User>> future3 = CompletableFuture.supplyAsync(() -> getUsers(25), executor);
    CompletableFuture<List<User>> future4 = CompletableFuture.supplyAsync(() -> getUsers(25), executor);

    List<User> allUsers = Stream.of(future1, future2, future3, future4)
                    .map(CompletableFuture::join)
                    .flatMap(List::stream)
                    .collect(Collectors.toList());
}


public static List<User> getUsers(int count) {
    List<User> users = new ArrayList<>();
    for (int i = 0; i < count; i++) {
        users.add(new User("someName", "someAge"));
        try {
            TimeUnit.MILLISECONDS.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
    return users;
}

如何异步调用一个方法并运行它？

How to call a method and run it asynchronously?

java

loops

list

completable-future

如何异步调用一个方法并 运行 它？

How to call a method and run it asynchronously?

java

loops

list

completable-future

如何异步调用一个方法并运行它？