BAEL-7001: retry RetryCompletableFuture

core-java-modules/core-java-concurrency-basic-3/src/main/java/com/baeldung/concurrent/completablefuture/retry/RetryCompletableFuture.java

@@ -0,0 +1,63 @@
+package com.baeldung.concurrent.completablefuture.retry;
+
+import java.util.concurrent.CompletableFuture;
+import java.util.function.Function;
+import java.util.function.Supplier;
+
+public class RetryCompletableFuture {
+	public static <T> CompletableFuture<T> retryTask(Supplier<T> supplier, int maxRetries) {
+		Supplier<T> retryableSupplier = retryFunction(supplier, maxRetries);
+		return CompletableFuture.supplyAsync(retryableSupplier);
+	}
+
+	static <T> Supplier<T> retryFunction(Supplier<T> supplier, int maxRetries) {
+		return () -> {
+			int retries = 0;
+			while (retries < maxRetries) {
+				try {
+					return supplier.get();
+				} catch (Exception e) {
+					retries++;
+				}
+			}
+			throw new IllegalStateException(String.format("Task failed after %s attempts", maxRetries));
+		};
+	}
+
+	public static <T> CompletableFuture<T> retryUnsafe(Supplier<T> supplier, int maxRetries) {
+		CompletableFuture<T> cf = CompletableFuture.supplyAsync(supplier);
+		sleep(100l);
+		for (int i = 0; i < maxRetries; i++) {
+			cf = cf.exceptionally(__ -> supplier.get());
+		}
+		return cf;
+	}
+
+	public static <T> CompletableFuture<T> retryNesting(Supplier<T> supplier, int maxRetries) {
+		CompletableFuture<T> cf = CompletableFuture.supplyAsync(supplier);
+		sleep(100);
+		for (int i = 0; i < maxRetries; i++) {
+			cf = cf.thenApply(CompletableFuture::completedFuture)
+			  .exceptionally(__ -> CompletableFuture.supplyAsync(supplier))
+			  .thenCompose(Function.identity());
+		}
+		return cf;
+	}
+
+	public static <T> CompletableFuture<T> retryExceptionallyAsync(Supplier<T> supplier, int maxRetries) {
+		CompletableFuture<T> cf = CompletableFuture.supplyAsync(supplier);
+		sleep(100);
+		for (int i = 0; i < maxRetries; i++) {
+			cf = cf.exceptionallyAsync(__ -> supplier.get());
+		}
+		return cf;
+	}
+
+	private static void sleep(long millis) {
+		try {
+			Thread.sleep(millis);
+		} catch (InterruptedException e) {
+			throw new RuntimeException(e);
+		}
+	}
+}

core-java-modules/core-java-concurrency-basic-3/src/test/java/com/baeldung/concurrent/completablefuture/retry/RetryCompletableFutureUnitTest.java

@@ -0,0 +1,125 @@
+package com.baeldung.concurrent.completablefuture.retry;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CompletionException;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.function.Supplier;
+
+import static com.baeldung.concurrent.completablefuture.retry.RetryCompletableFuture.*;
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+class RetryCompletableFutureUnitTest {
+	private AtomicInteger retriesCounter = new AtomicInteger(0);
+
+	@BeforeEach
+	void beforeEach() {
+		retriesCounter.set(0);
+	}
+
+	@Test
+	void whenRetryingTask_thenReturnsCorrectlyAfterFourInvocations() {
+		Supplier<Integer> codeToRun = () -> failFourTimesThenReturn(100);
+
+		CompletableFuture<Integer> result = retryTask(codeToRun, 10);
+
+		assertThat(result.join())
+		  .isEqualTo(100);
+		assertThat(retriesCounter)
+		  .hasValue(4);
+	}
+
+	@Test
+	void whenRetryingTask_thenThrowsExceptionAfterThreeInvocations() {
+		Supplier<Integer> codeToRun = () -> failFourTimesThenReturn(100);
+
+		CompletableFuture<Integer> result = retryTask(codeToRun, 3);
+
+		assertThatThrownBy(result::join)
+		  .isInstanceOf(CompletionException.class)
+		  .hasMessageContaining("IllegalStateException: Task failed after 3 attempts");
+	}
+
+	@Test
+	void whenRetryingExceptionally_thenReturnsCorrectlyAfterFourInvocations() {
+		Supplier<Integer> codeToRun = () -> failFourTimesThenReturn(100);
+
+		CompletableFuture<Integer> result = retryUnsafe(codeToRun, 10);
+
+		assertThat(result.join())
+		  .isEqualTo(100);
+		assertThat(retriesCounter)
+		  .hasValue(4);
+	}
+
+	@Test
+	void whenRetryingExceptionally_thenThrowsExceptionAfterThreeInvocations() {
+		Supplier<Integer> codeToRun = () -> failFourTimesThenReturn(100);
+
+		CompletableFuture<Integer> result = retryUnsafe(codeToRun, 3);
+
+		assertThatThrownBy(result::join)
+		  .isInstanceOf(CompletionException.class)
+		  .hasMessageContaining("RuntimeException: task failed for 3 time(s)");
+	}
+
+	@Test
+	void whenRetryingExceptionallyAsync_thenReturnsCorrectlyAfterFourInvocations() {
+		Supplier<Integer> codeToRun = () -> failFourTimesThenReturn(100);
+
+		CompletableFuture<Integer> result = retryExceptionallyAsync(codeToRun, 10);
+
+		assertThat(result.join())
+		  .isEqualTo(100);
+		assertThat(retriesCounter)
+		  .hasValue(4);
+	}
+
+	@Test
+	void whenRetryingExceptionallyAsync_thenThrowsExceptionAfterThreeInvocations() {
+		Supplier<Integer> codeToRun = () -> failFourTimesThenReturn(100);
+
+		CompletableFuture<Integer> result = retryExceptionallyAsync(codeToRun, 3);
+
+		assertThatThrownBy(result::join)
+		  .isInstanceOf(CompletionException.class)
+		  .hasMessageContaining("RuntimeException: task failed for 3 time(s)");
+	}
+
+	@Test
+	void whenRetryingNesting_thenReturnsCorrectlyAfterFourInvocations() {
+		Supplier<Integer> codeToRun = () -> failFourTimesThenReturn(100);
+
+		CompletableFuture<Integer> result = retryNesting(codeToRun, 10);
+
+		assertThat(result.join())
+		  .isEqualTo(100);
+		assertThat(retriesCounter)
+		  .hasValue(4);
+	}
+
+	@Test
+	void whenRetryingNesting_thenThrowsExceptionAfterThreeInvocations() {
+		Supplier<Integer> codeToRun = () -> failFourTimesThenReturn(100);
+
+		CompletableFuture<Integer> result = retryNesting(codeToRun, 3);
+
+		assertThatThrownBy(result::join)
+		  .isInstanceOf(CompletionException.class)
+		  .hasMessageContaining("RuntimeException: task failed for 3 time(s)");
+	}
+
+	int failFourTimesThenReturn(int returnValue) {
+		int retryNr = retriesCounter.get();
+		System.out.println(String.format("invocation: %s, thread: %s", retryNr, Thread.currentThread().getName()));
+		if (retryNr < 4) {
+			retriesCounter.set(retryNr + 1);
+			throw new RuntimeException(String.format("task failed for %s time(s)", retryNr));
+		}
+		return returnValue;
+	}
+
+}