Added test for the Guide to CompletableFuture (#611)

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<String> completableFuture = calculateAsync();
+
+        String result = completableFuture.get();
+        assertEquals("Hello", result);
+
+    }
+
+    public Future<String> calculateAsync() throws InterruptedException {
+        CompletableFuture<String> 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<String> completableFuture = CompletableFuture.completedFuture("Hello");
+
+        String result = completableFuture.get();
+        assertEquals("Hello", result);
+
+    }
+
+    @Test
+    public void whenCreatingCompletableFutureWithSupplyAsync_thenFutureReturnsValue() throws ExecutionException, InterruptedException {
+
+        CompletableFuture<String> future = CompletableFuture.supplyAsync(() -> "Hello");
+
+        assertEquals("Hello", future.get());
+
+    }
+
+    @Test
+    public void whenAddingThenAcceptToFuture_thenFunctionExecutesAfterComputationIsFinished() throws ExecutionException, InterruptedException {
+
+        CompletableFuture<String> completableFuture = CompletableFuture.supplyAsync(() -> "Hello");
+
+        CompletableFuture<Void> future = completableFuture.thenAccept(s -> System.out.println("Computation returned: " + s));
+
+        future.get();
+
+    }
+
+    @Test
+    public void whenAddingThenRunToFuture_thenFunctionExecutesAfterComputationIsFinished() throws ExecutionException, InterruptedException {
+
+        CompletableFuture<String> completableFuture = CompletableFuture.supplyAsync(() -> "Hello");
+
+        CompletableFuture<Void> future = completableFuture.thenRun(() -> System.out.println("Computation finished."));
+
+        future.get();
+
+    }
+
+    @Test
+    public void whenAddingThenApplyToFuture_thenFunctionExecutesAfterComputationIsFinished() throws ExecutionException, InterruptedException {
+
+        CompletableFuture<String> completableFuture = CompletableFuture.supplyAsync(() -> "Hello");
+
+        CompletableFuture<String> future = completableFuture.thenApply(s -> s + " World");
+
+        assertEquals("Hello World", future.get());
+
+    }
+
+    @Test
+    public void whenUsingThenCompose_thenFuturesExecuteSequentially() throws ExecutionException, InterruptedException {
+
+        CompletableFuture<String> completableFuture = CompletableFuture.supplyAsync(() -> "Hello")
+                .thenCompose(s -> CompletableFuture.supplyAsync(() -> s + " World"));
+
+        assertEquals("Hello World", completableFuture.get());
+
+    }
+
+    @Test
+    public void whenUsingThenCombine_thenWaitForExecutionOfBothFutures() throws ExecutionException, InterruptedException {
+
+        CompletableFuture<String> 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<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());
+
+        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<String> 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<String> completableFuture = new CompletableFuture<>();
+
+        // ...
+
+        completableFuture.completeExceptionally(new RuntimeException("Calculation failed!"));
+
+        // ...
+
+        completableFuture.get();
+
+    }
+
+    @Test
+    public void whenAddingThenApplyAsyncToFuture_thenFunctionExecutesAfterComputationIsFinished() throws ExecutionException, InterruptedException {
+
+        CompletableFuture<String> completableFuture = CompletableFuture.supplyAsync(() -> "Hello");
+
+        CompletableFuture<String> future = completableFuture.thenApplyAsync(s -> s + " World");
+
+        assertEquals("Hello World", future.get());
+
+    }
+
+}