Merge pull request #14978 from etrandafir93/features/BAEL-7001-retry_completable_future

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 +1,120 @@
+package com.baeldung.concurrent.completablefuture.retry;
+
+import static com.baeldung.concurrent.completablefuture.retry.RetryCompletableFuture.retryExceptionallyAsync;
+import static com.baeldung.concurrent.completablefuture.retry.RetryCompletableFuture.retryNesting;
+import static com.baeldung.concurrent.completablefuture.retry.RetryCompletableFuture.retryTask;
+import static com.baeldung.concurrent.completablefuture.retry.RetryCompletableFuture.retryUnsafe;
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CompletionException;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.function.Supplier;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+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;
+    }
+
+}