Support for one-time tasks with just @Scheduled(initialDelay=...)

Closes gh-31211

spring-context/src/test/java/org/springframework/scheduling/annotation/EnableSchedulingTests.java

@@ -218,15 +218,6 @@ public class EnableSchedulingTests {
 		assertThat(ctx.getBean(ThreadAwareWorker.class).executedByThread).startsWith("taskScheduler-");
 	}
 
-	@Test
-	@EnabledForTestGroups(LONG_RUNNING)
-	public void withTriggerTask() throws InterruptedException {
-		ctx = new AnnotationConfigApplicationContext(TriggerTaskConfig.class);
-
-		Thread.sleep(110);
-		assertThat(ctx.getBean(AtomicInteger.class).get()).isGreaterThan(1);
-	}
-
 	@Test
 	@EnabledForTestGroups(LONG_RUNNING)
 	public void withInitiallyDelayedFixedRateTask() throws InterruptedException {
@@ -235,9 +226,30 @@ public class EnableSchedulingTests {
 		Thread.sleep(1950);
 		AtomicInteger counter = ctx.getBean(AtomicInteger.class);
 
-		// The @Scheduled method should have been called at least once but
-		// not more times than the delay allows.
-		assertThat(counter.get()).isBetween(1, 10);
+		// The @Scheduled method should have been called several times
+		// but not more times than the delay allows.
+		assertThat(counter.get()).isBetween(2, 10);
+	}
+
+	@Test
+	@EnabledForTestGroups(LONG_RUNNING)
+	public void withOneTimeTask() throws InterruptedException {
+		ctx = new AnnotationConfigApplicationContext(OneTimeTaskConfig.class);
+
+		Thread.sleep(110);
+		AtomicInteger counter = ctx.getBean(AtomicInteger.class);
+
+		// The @Scheduled method should have been called exactly once.
+		assertThat(counter.get()).isEqualTo(1);
+	}
+
+	@Test
+	@EnabledForTestGroups(LONG_RUNNING)
+	public void withTriggerTask() throws InterruptedException {
+		ctx = new AnnotationConfigApplicationContext(TriggerTaskConfig.class);
+
+		Thread.sleep(110);
+		assertThat(ctx.getBean(AtomicInteger.class).get()).isGreaterThan(1);
 	}
 
 
@@ -598,6 +610,38 @@ public class EnableSchedulingTests {
 	}
 
 
+	@Configuration
+	@EnableScheduling
+	static class FixedRateTaskConfig_withInitialDelay {
+
+		@Bean
+		public AtomicInteger counter() {
+			return new AtomicInteger();
+		}
+
+		@Scheduled(initialDelay = 1000, fixedRate = 100)
+		public void task() {
+			counter().incrementAndGet();
+		}
+	}
+
+
+	@Configuration
+	@EnableScheduling
+	static class OneTimeTaskConfig {
+
+		@Bean
+		public AtomicInteger counter() {
+			return new AtomicInteger();
+		}
+
+		@Scheduled(initialDelay = 10)
+		public void task() {
+			counter().incrementAndGet();
+		}
+	}
+
+
 	@Configuration
 	static class TriggerTaskConfig {
 
@@ -616,20 +660,4 @@ public class EnableSchedulingTests {
 		}
 	}
 
-
-	@Configuration
-	@EnableScheduling
-	static class FixedRateTaskConfig_withInitialDelay {
-
-		@Bean
-		public AtomicInteger counter() {
-			return new AtomicInteger();
-		}
-
-		@Scheduled(initialDelay = 1000, fixedRate = 100)
-		public void task() {
-			counter().incrementAndGet();
-		}
-	}
-
 }

spring-context/src/test/java/org/springframework/scheduling/annotation/ScheduledAnnotationBeanPostProcessorTests.java

@@ -57,6 +57,7 @@ import org.springframework.scheduling.Trigger;
 import org.springframework.scheduling.TriggerContext;
 import org.springframework.scheduling.config.CronTask;
 import org.springframework.scheduling.config.IntervalTask;
+import org.springframework.scheduling.config.OneTimeTask;
 import org.springframework.scheduling.config.ScheduledTaskHolder;
 import org.springframework.scheduling.config.ScheduledTaskRegistrar;
 import org.springframework.scheduling.support.CronTrigger;
@@ -266,6 +267,33 @@ class ScheduledAnnotationBeanPostProcessorTests {
 		assertThat(task2.getIntervalDuration()).isEqualTo(Duration.ofMillis(4_000L));
 	}
 
+	@Test
+	void oneTimeTask() {
+		BeanDefinition processorDefinition = new RootBeanDefinition(ScheduledAnnotationBeanPostProcessor.class);
+		BeanDefinition targetDefinition = new RootBeanDefinition(OneTimeTaskBean.class);
+		context.registerBeanDefinition("postProcessor", processorDefinition);
+		context.registerBeanDefinition("target", targetDefinition);
+		context.refresh();
+
+		ScheduledTaskHolder postProcessor = context.getBean("postProcessor", ScheduledTaskHolder.class);
+		assertThat(postProcessor.getScheduledTasks()).hasSize(1);
+
+		Object target = context.getBean("target");
+		ScheduledTaskRegistrar registrar = (ScheduledTaskRegistrar)
+				new DirectFieldAccessor(postProcessor).getPropertyValue("registrar");
+		@SuppressWarnings("unchecked")
+		List<OneTimeTask> oneTimeTasks = (List<OneTimeTask>)
+				new DirectFieldAccessor(registrar).getPropertyValue("oneTimeTasks");
+		assertThat(oneTimeTasks).hasSize(1);
+		OneTimeTask task = oneTimeTasks.get(0);
+		ScheduledMethodRunnable runnable = (ScheduledMethodRunnable) task.getRunnable();
+		Object targetObject = runnable.getTarget();
+		Method targetMethod = runnable.getMethod();
+		assertThat(targetObject).isEqualTo(target);
+		assertThat(targetMethod.getName()).isEqualTo("oneTimeTask");
+		assertThat(task.getInitialDelayDuration()).isEqualTo(Duration.ofMillis(2_000L));
+	}
+
 	@Test
 	void cronTask() {
 		BeanDefinition processorDefinition = new RootBeanDefinition(ScheduledAnnotationBeanPostProcessor.class);
@@ -848,6 +876,14 @@ class ScheduledAnnotationBeanPostProcessorTests {
 	}
 
 
+	static class OneTimeTaskBean {
+
+		@Scheduled(initialDelay = 2_000)
+		private void oneTimeTask() {
+		}
+	}
+
+
 	@Validated
 	static class CronTestBean {