When we want to execute a background activity task asynchronously and do not want to return anything from that task, we can use the CompletableFuture.runAsync() method. It takes a parameter as a Runnable object and returns the CompletableFuture<Void> type.

Let's try to use the runAsync() method by creating another controller method in our BankController class, with the following example:

@RequestMapping(value = "/synccust")
  @ResponseBody
  public CompletableFuture<String> syncCustomerDetails() {
    LOGGER.info("Entering in controller");

    CompletableFuture<String> completableFuture = new 
    CompletableFuture<>();
    CompletableFuture.runAsync(new Runnable() {
      
      @Override
      public void run() {
        try {           
           completableFuture.complete(syncService.syncCustomerAccount()
           .get());
        } catch (InterruptedException | ExecutionException e) {
          completableFuture.completeExceptionally(e);
        }
        
      }
    }); 
      LOGGER.info("Leaving from controller");
      return completableFuture;
  }

In the preceding example, when a request comes with the /synccust path, it will run syncCustomerAccount() in a separate thread and will complete the task without returning any value.