User problem: Fetch the order summary of a certain customer.

This time, the asynchronous task must return a result, and so runAsync() is not useful. This is a job for supplyAsync(). It takes  Supplier<T> and returns CompletableFuture<T>. T is the type of the result obtained from this supplier via the get() method. In code lines, we can solve this problem as follows:

public static void fetchOrderSummary() {

  CompletableFuture<String> cfOrderSummary 
      = CompletableFuture.supplyAsync(() -> {

    logger.info(() -> "Fetch order summary by: "
      + Thread.currentThread().getName());
    Thread.sleep(500);

    return "Order Summary #93443";
  });

  // wait for summary to be available, this is blocking
  String summary = cfOrderSummary.get();
  logger.info(() -> "Order summary: " + summary + "
");
}