CompletionException Sınıfı

Giriş

Şu satırı dahil ederiz

import java.util.concurrent.CompletionException;

- Bir CompletableFuture'a join() yaparsak ve CompletableFuture exception ile biterse, CompletionException fırlatılır.

- Bir CompletableFuture'a get() yaparsak ve CompletableFuture exception ile biterse, ExecutionException  fırlatılır.

Örnek - ArithmeticException

Şöyle yaparız

CompletableFuture<Void> completableFuture = CompletableFuture
  .supplyAsync(() -> {
    System.out.println("running task");
    return 1 / 0;
  })
  .thenApply(input -> {
    System.out.println("multiplying by 2");
    return input * 2;
  })
  .thenAccept(System.out::println);

  Thread.sleep(3000);//let the stages complete
  System.out.println("-- checking exceptions --");
  try {
    completableFuture.join();
  } catch (CompletionException exception) {
    exception.printStackTrace();
  }
  //compile error
  //} catch (ExecutionException exception) {
  //    exception.printStackTrace();
  //}

printStackTrace() çıktısı şöyle. "Caused by" kısmında exception'ının hangi satırdan geldiği gösteriliyor.

java.util.concurrent.CompletionException: java.lang.ArithmeticException: / by zero
  at java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:273)
  at java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:280)
  at java.util.concurrent.CompletableFuture$AsyncSupply.run$$$capture(CompletableFuture.java:1606)
  at java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java)
  at java.util.concurrent.CompletableFuture$AsyncSupply.exec(CompletableFuture.java:1596)
  at java.util.concurrent.ForkJoinTask.doExec$$$capture(ForkJoinTask.java:289)
  at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java)
  at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1056)
  at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1692)
 at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:175)
Caused by: java.lang.ArithmeticException: / by zero
  at Scratch.lambda$join$0(scratch.java:13)
  at java.util.concurrent.CompletableFuture$AsyncSupply.run$$$capture(CompletableFuture.java:1604)
  ... 7 more

Örnek - completeExceptionally

Şöyle yaparız

CompletableFuture<Double> completableFuture = CompletableFuture
  .supplyAsync(() -> {
    System.out.println("running task");
    return 2.0;
  });


completableFuture.completeExceptionally(new RuntimeException("my error"));


Thread.sleep(3000);//let the stages complete
System.out.println("-- checking exceptions --");
try {
  completableFuture.join();
} catch (CompletionException exception) {
   exception.printStackTrace();
}

printStackTrace() çıktısı şöyle. "Caused by" kısmında exception'ının hangi satırdan geldiği gösteriliyor.

java.util.concurrent.CompletionException: java.lang.RuntimeException: my error
  at java.util.concurrent.CompletableFuture.reportJoin(CompletableFuture.java:375)
  at java.util.concurrent.CompletableFuture.join(CompletableFuture.java:1947)
  at Scratch.join2(scratch_6.java:49)
  at Scratch.main(scratch_6.java:83)
Caused by: java.lang.RuntimeException: my error
  at Scratch.join2(scratch.java:43)
  ... 1 more