BAEL-7187 implemented (#15208)

* BAEL-7139 implemented

* BAEL-7187 implemented

core-java-modules/core-java-concurrency-advanced-5/src/test/java/com/baeldung/exceptions_completablefuture/CompletableFutureExceptionsHandlingUnitTest.java

@@ -0,0 +1,126 @@
+package com.baeldung.exceptions_completablefuture;
+
+import java.util.List;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutionException;
+import java.util.stream.Stream;
+
+import org.assertj.core.api.Assertions;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+
+public class CompletableFutureExceptionsHandlingUnitTest {
+
+    @ParameterizedTest
+    @MethodSource("parametersSource_handle")
+    void whenCompletableFutureIsScheduled_thenHandleStageIsAlwaysInvoked(int radius, long expected)
+      throws ExecutionException, InterruptedException {
+        long actual = CompletableFuture
+          .supplyAsync(() -> {
+              if (radius <= 0) {
+                  throw new IllegalArgumentException("Supplied with non-positive radius '%d'");
+              }
+              return Math.round(Math.pow(radius, 2) * Math.PI);
+          })
+          .handle((result, ex) -> {
+              if (ex == null) {
+                  return result;
+              } else {
+                  return -1L;
+              }
+          })
+          .get();
+
+        Assertions.assertThat(actual).isEqualTo(expected);
+    }
+
+    @ParameterizedTest
+    @MethodSource("parametersSource_exceptionally")
+    void whenCompletableFutureIsScheduled_thenExceptionallyExecutedOnlyOnFailure(int a, int b, int c, long expected)
+      throws ExecutionException, InterruptedException {
+        long actual = CompletableFuture
+          .supplyAsync(() -> {
+              if (a <= 0 || b <= 0 || c <= 0) {
+                  throw new IllegalArgumentException(String.format("Supplied with incorrect edge length [%s]", List.of(a, b, c)));
+              }
+              return a * b * c;
+          })
+          .exceptionally((ex) -> -1)
+          .get();
+
+        Assertions.assertThat(actual).isEqualTo(expected);
+    }
+
+    @ParameterizedTest
+    @MethodSource("parametersSource_exceptionally")
+    void givenCompletableFutureIsScheduled_whenHandleIsAlreadyPresent_thenExceptionallyIsNotExecuted(int a, int b, int c, long expected)
+      throws ExecutionException, InterruptedException {
+        long actual = CompletableFuture
+          .supplyAsync(() -> {
+              if (a <= 0 || b <= 0 || c <= 0) {
+                  throw new IllegalArgumentException(String.format("Supplied with incorrect edge length [%s]", List.of(a, b, c)));
+              }
+              return a * b * c;
+          })
+          .handle((result, throwable) -> {
+              if (throwable != null) {
+                  return -1;
+              }
+              return result;
+          })
+          .exceptionally((ex) -> {
+              System.exit(1);
+              return 0;
+          })
+          .get();
+
+        Assertions.assertThat(actual).isEqualTo(expected);
+    }
+
+    @ParameterizedTest
+    @MethodSource("parametersSource_whenComplete")
+    void whenCompletableFutureIsScheduled_thenWhenCompletedExecutedAlways(Double a, long expected, Class<Exception> ifAny) {
+        try {
+            CountDownLatch countDownLatch = new CountDownLatch(1);
+
+            long actual = CompletableFuture
+              .supplyAsync(() -> {
+                  if (a.isNaN()) {
+                      throw new IllegalArgumentException("Supplied value is NaN");
+                  }
+                  return Math.round(Math.pow(a, 2));
+              })
+              .whenComplete((result, exception) -> countDownLatch.countDown())
+              .get();
+
+            Assertions.assertThat(countDownLatch.await(20L, java.util.concurrent.TimeUnit.SECONDS));
+            Assertions.assertThat(actual).isEqualTo(expected);
+        } catch (Exception e) {
+            Assertions.assertThat(e.getClass()).isSameAs(ExecutionException.class);
+            Assertions.assertThat(e.getCause().getClass()).isSameAs(ifAny);
+        }
+    }
+
+    static Stream<Arguments> parametersSource_handle() {
+        return Stream.of(
+          Arguments.of(1, 3),
+          Arguments.of(-1, -1)
+        );
+    }
+
+    static Stream<Arguments> parametersSource_exceptionally() {
+        return Stream.of(
+          Arguments.of(1, 5, 5, 25),
+          Arguments.of(-1, 10, 15, -1)
+        );
+    }
+
+    static Stream<Arguments> parametersSource_whenComplete() {
+        return Stream.of(
+          Arguments.of(2d, 4, null),
+          Arguments.of(Double.NaN, 1, IllegalArgumentException.class)
+        );
+    }
+}