Wait for the async callback function to return in java

Question

final Function<Boolean, ? extends Class<Void>> functionCallback = (Boolean t) -> {
   if(t) {
     plugin.setIsInstalled(Boolean.TRUE);             
   }
   return Void.TYPE;
};

foo.install(plugin,functionCallback);

if(plugin.getIsInstalled().getValue())
  return "done";
else 
  return "not done";

I want to check if(plugin.getIsInstalled().getValue()) once the callback has finished executing. How can I prevent execution of this if condition until callback has completed execution?

BooleanProperty of javafx package. This property is set inside callback function which I want to access once callback has finished execution — pratik ashani
– pratik ashani, Commented Mar 12, 2019 at 17:05

Lothar · Accepted Answer · 2019-03-12 21:15:14Z

7

You can use a FutureTask that gets called in your callback function:

final FutureTask<Object> ft = new FutureTask<Object>(() -> {}, new Object());
final Function<Boolean, ? extends Class<Void>> functionCallback = (Boolean t) -> {
    if(t) {
        plugin.setIsInstalled(Boolean.TRUE);
        ft.run();
    }
    return Void.TYPE;
};

foo.install(plugin,functionCallback); 
ft.get();
if(plugin.getIsInstalled().getValue())
    return "done";
else 
    return "not done";

Future.get waits till the run method was called, you can also use the get-method that accepts a timeout so you can react on that if it takes too long.

edited Mar 12, 2019 at 21:15

answered Mar 12, 2019 at 17:44

Lothar

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Prathik Rajendran M · Accepted Answer · 2019-03-12 18:07:17Z

3

You can use a CountDownLatch or a ReentrantLock that gets released when the function is run.
Your foo#install can return a CompletableFuture and you can consume the results as follows

CompletableFuture<Integer> future = CompletableFuture.supplyAsync(() -> 1);
future.thenAccept((v) -> System.out.println("v = " + v));

Function itself has an andThen method which you can use to run whatever is required post apply.

answered Mar 12, 2019 at 18:07

Prathik Rajendran M

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Comments

Dharmu Immannavar · Accepted Answer · 2019-03-12 17:19:27Z

-1

The callback is mostly used to perform a task after a particular task is done. So it better separate the code you want to execute into a different function call that function.

If you want to execute something after callback have nested callbacks.

answered Mar 12, 2019 at 17:19

Dharmu Immannavar

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