CompletableFuture

CompletableFuture 

Example

supplyAsync 메서드를 이용한 방식

CompletableFuture<String> future

  = CompletableFuture.supplyAsync(() -> "Hello");

 

// ...

 

assertEquals("Hello", future.get());

thenApply 메서드를 이용한 결과값 처리

CompletableFuture<String> completableFuture

  = CompletableFuture.supplyAsync(() -> "Hello");

 

CompletableFuture<String> future = completableFuture

  .thenApply(s -> s + " World");

 

assertEquals("Hello World", future.get());

thenCompose를 이용하여 Future을 이용하여 처리하기

CompletableFuture<String> completableFuture 

  = CompletableFuture.supplyAsync(() -> "Hello")

    .thenCompose(s -> CompletableFuture.supplyAsync(() -> s + " World"));

 

assertEquals("Hello World", completableFuture.get());

multiple futures

CompletableFuture<String> future1  

  = CompletableFuture.supplyAsync(() -> "Hello");

CompletableFuture<String> future2  

  = CompletableFuture.supplyAsync(() -> "Beautiful");

CompletableFuture<String> future3  

  = CompletableFuture.supplyAsync(() -> "World");

 

CompletableFuture<Void> combinedFuture 

  = CompletableFuture.allOf(future1, future2, future3);

 

// ...

 

combinedFuture.get();

 

assertTrue(future1.isDone());

assertTrue(future2.isDone());

assertTrue(future3.isDone());

stream을 이용하여 결과값 합치기

String combined = Stream.of(future1, future2, future3)

  .map(CompletableFuture::join)

  .collect(Collectors.joining(" "));

 

assertEquals("Hello Beautiful World", combined);

에러 핸들링

String name = null;

 

// ...

 

CompletableFuture<String> completableFuture  

  =  CompletableFuture.supplyAsync(() -> {

      if (name == null) {

          throw new RuntimeException("Computation error!");

      }

      return "Hello, " + name;

  })}).handle((s, t) -> s != null ? s : "Hello, Stranger!");

 

assertEquals("Hello, Stranger!", completableFuture.get());

Async Method

CompletableFuture<String> completableFuture  

  = CompletableFuture.supplyAsync(() -> "Hello");

 

CompletableFuture<String> future = completableFuture

  .thenApplyAsync(s -> s + " World");

 

assertEquals("Hello World", future.get());

Custom ExecutorService

private static ExecutorService service = Executors.newCachedThreadPool();

CompletableFuture<Void> runAsync = CompletableFuture.runAsync(() -> System.out.println("running async task"), service);

• 기본적으로 PorkJoinPool.commonPool()를 사용하기 때문에 Executor Service를 활용해서 성능을 상승 시킬수가 있다.