diff --git a/core-java-8/src/test/java/com/baeldung/completablefuture/CompletableFutureTest.java b/core-java-8/src/test/java/com/baeldung/completablefuture/CompletableFutureTest.java new file mode 100644 index 0000000000..47700f60c7 --- /dev/null +++ b/core-java-8/src/test/java/com/baeldung/completablefuture/CompletableFutureTest.java @@ -0,0 +1,196 @@ +package com.baeldung.completablefuture; + +import java.util.concurrent.CompletableFuture; +import java.util.concurrent.ExecutionException; +import java.util.concurrent.Executors; +import java.util.concurrent.Future; +import java.util.stream.Collectors; +import java.util.stream.Stream; + +import org.junit.Test; + +import static org.junit.Assert.assertEquals; +import static org.junit.Assert.assertTrue; + +public class CompletableFutureTest { + + @Test + public void whenRunningCompletableFutureAsyncronously_thenGetMethodWaitsForResult() throws InterruptedException, ExecutionException { + + Future completableFuture = calculateAsync(); + + String result = completableFuture.get(); + assertEquals("Hello", result); + + } + + public Future calculateAsync() throws InterruptedException { + CompletableFuture completableFuture = new CompletableFuture<>(); + + Executors.newCachedThreadPool().submit(() -> { + Thread.sleep(500); + completableFuture.complete("Hello"); + return null; + }); + + return completableFuture; + } + + @Test + public void whenRunningCompletableFutureWithResult_thenGetMethodReturnsImmediately() throws InterruptedException, ExecutionException { + + Future completableFuture = CompletableFuture.completedFuture("Hello"); + + String result = completableFuture.get(); + assertEquals("Hello", result); + + } + + @Test + public void whenCreatingCompletableFutureWithSupplyAsync_thenFutureReturnsValue() throws ExecutionException, InterruptedException { + + CompletableFuture future = CompletableFuture.supplyAsync(() -> "Hello"); + + assertEquals("Hello", future.get()); + + } + + @Test + public void whenAddingThenAcceptToFuture_thenFunctionExecutesAfterComputationIsFinished() throws ExecutionException, InterruptedException { + + CompletableFuture completableFuture = CompletableFuture.supplyAsync(() -> "Hello"); + + CompletableFuture future = completableFuture.thenAccept(s -> System.out.println("Computation returned: " + s)); + + future.get(); + + } + + @Test + public void whenAddingThenRunToFuture_thenFunctionExecutesAfterComputationIsFinished() throws ExecutionException, InterruptedException { + + CompletableFuture completableFuture = CompletableFuture.supplyAsync(() -> "Hello"); + + CompletableFuture future = completableFuture.thenRun(() -> System.out.println("Computation finished.")); + + future.get(); + + } + + @Test + public void whenAddingThenApplyToFuture_thenFunctionExecutesAfterComputationIsFinished() throws ExecutionException, InterruptedException { + + CompletableFuture completableFuture = CompletableFuture.supplyAsync(() -> "Hello"); + + CompletableFuture future = completableFuture.thenApply(s -> s + " World"); + + assertEquals("Hello World", future.get()); + + } + + @Test + public void whenUsingThenCompose_thenFuturesExecuteSequentially() throws ExecutionException, InterruptedException { + + CompletableFuture completableFuture = CompletableFuture.supplyAsync(() -> "Hello") + .thenCompose(s -> CompletableFuture.supplyAsync(() -> s + " World")); + + assertEquals("Hello World", completableFuture.get()); + + } + + @Test + public void whenUsingThenCombine_thenWaitForExecutionOfBothFutures() throws ExecutionException, InterruptedException { + + CompletableFuture completableFuture = CompletableFuture.supplyAsync(() -> "Hello") + .thenCombine(CompletableFuture.supplyAsync(() -> " World"), + (s1, s2) -> s1 + s2); + + assertEquals("Hello World", completableFuture.get()); + + } + + @Test + public void whenUsingThenAcceptBoth_thenWaitForExecutionOfBothFutures() throws ExecutionException, InterruptedException { + + CompletableFuture.supplyAsync(() -> "Hello") + .thenAcceptBoth(CompletableFuture.supplyAsync(() -> " World"), + (s1, s2) -> System.out.println(s1 + s2)); + + } + + @Test + public void whenFutureCombinedWithAllOfCompletes_thenAllFuturesAreDone() throws ExecutionException, InterruptedException { + + CompletableFuture future1 = CompletableFuture.supplyAsync(() -> "Hello"); + CompletableFuture future2 = CompletableFuture.supplyAsync(() -> "Beautiful"); + CompletableFuture future3 = CompletableFuture.supplyAsync(() -> "World"); + + CompletableFuture combinedFuture = CompletableFuture.allOf(future1, future2, future3); + + // ... + + combinedFuture.get(); + + assertTrue(future1.isDone()); + assertTrue(future2.isDone()); + assertTrue(future3.isDone()); + + String combined = Stream.of(future1, future2, future3) + .map(CompletableFuture::join) + .collect(Collectors.joining(" ")); + + assertEquals("Hello Beautiful World", combined); + + } + + @Test + public void whenFutureThrows_thenHandleMethodRecievesException() throws ExecutionException, InterruptedException { + + String name = null; + + // ... + + CompletableFuture completableFuture = CompletableFuture.supplyAsync(() -> { + if (name == null) { + throw new RuntimeException("Computation error!"); + } + return "Hello, " + name; + }).handle((s, t) -> { + if (s != null) { + return s; + } else { + return "Hello, Stranger!"; + } + }); + + assertEquals("Hello, Stranger!", completableFuture.get()); + + } + + @Test(expected = ExecutionException.class) + public void whenCompletingFutureExceptionally_thenGetMethodThrows() throws ExecutionException, InterruptedException { + + CompletableFuture completableFuture = new CompletableFuture<>(); + + // ... + + completableFuture.completeExceptionally(new RuntimeException("Calculation failed!")); + + // ... + + completableFuture.get(); + + } + + @Test + public void whenAddingThenApplyAsyncToFuture_thenFunctionExecutesAfterComputationIsFinished() throws ExecutionException, InterruptedException { + + CompletableFuture completableFuture = CompletableFuture.supplyAsync(() -> "Hello"); + + CompletableFuture future = completableFuture.thenApplyAsync(s -> s + " World"); + + assertEquals("Hello World", future.get()); + + } + +}