Add execution metadata to scheduled tasks actuator endpoint

As of spring-projects/spring-framework#24560, Spring provides additional
metadata for scheduled tasks:
* next execution time
* last execution outcome (including status, time and raised exception)

This commit leverages this information to enhance the existing
`scheduledtasks` Actuator endpoint.

Closes gh-17585

Author: bclozel

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/endpoint/web/documentation/ScheduledTasksEndpointDocumentationTests.java

@@ -27,11 +27,13 @@
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.Import;
 import org.springframework.restdocs.payload.FieldDescriptor;
+import org.springframework.restdocs.payload.JsonFieldType;
 import org.springframework.scheduling.Trigger;
 import org.springframework.scheduling.TriggerContext;
 import org.springframework.scheduling.annotation.EnableScheduling;
 import org.springframework.scheduling.annotation.Scheduled;
 import org.springframework.scheduling.annotation.SchedulingConfigurer;
+import org.springframework.scheduling.concurrent.SimpleAsyncTaskScheduler;
 import org.springframework.scheduling.config.ScheduledTaskHolder;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -57,9 +59,12 @@ void scheduledTasks() {
 							"com.example.Processor")),
 					responseFields(fieldWithPath("cron").description("Cron tasks, if any."),
 							targetFieldWithPrefix("cron.[]."),
+							nextExecutionWithPrefix("cron.[].").description("Time of the next scheduled execution."),
 							fieldWithPath("cron.[].expression").description("Cron expression."),
 							fieldWithPath("fixedDelay").description("Fixed delay tasks, if any."),
 							targetFieldWithPrefix("fixedDelay.[]."), initialDelayWithPrefix("fixedDelay.[]."),
+							nextExecutionWithPrefix("fixedDelay.[].")
+								.description("Time of the next scheduled execution."),
 							fieldWithPath("fixedDelay.[].interval")
 								.description("Interval, in milliseconds, between the end of the last"
 										+ " execution and the start of the next."),
@@ -68,9 +73,15 @@ void scheduledTasks() {
 							fieldWithPath("fixedRate.[].interval")
 								.description("Interval, in milliseconds, between the start of each execution."),
 							initialDelayWithPrefix("fixedRate.[]."),
+							nextExecutionWithPrefix("fixedRate.[].")
+								.description("Time of the next scheduled execution."),
 							fieldWithPath("custom").description("Tasks with custom triggers, if any."),
 							targetFieldWithPrefix("custom.[]."),
-							fieldWithPath("custom.[].trigger").description("Trigger for the task."))));
+							fieldWithPath("custom.[].trigger").description("Trigger for the task."))
+						.andWithPrefix("*.[].",
+								fieldWithPath("lastExecution").description("Last execution of this task, if any.")
+									.optional())
+						.andWithPrefix("*.[].lastExecution.", lastExecution())));
 	}
 
 	private FieldDescriptor targetFieldWithPrefix(String prefix) {
@@ -81,6 +92,22 @@ private FieldDescriptor initialDelayWithPrefix(String prefix) {
 		return fieldWithPath(prefix + "initialDelay").description("Delay, in milliseconds, before first execution.");
 	}
 
+	private FieldDescriptor nextExecutionWithPrefix(String prefix) {
+		return fieldWithPath(prefix + "nextExecution.time").description("Time of the next scheduled execution.");
+	}
+
+	private FieldDescriptor[] lastExecution() {
+		return new FieldDescriptor[] {
+				fieldWithPath("status").description("Status of the last execution (STARTED, SUCCESS, ERROR)."),
+				fieldWithPath("time").description("Time of the last execution.").type(JsonFieldType.STRING),
+				fieldWithPath("exception.type").description("Exception type thrown by the task, if any.")
+					.type(JsonFieldType.STRING)
+					.optional(),
+				fieldWithPath("exception.message").description("Message of the exception thrown by the task, if any.")
+					.type(JsonFieldType.STRING)
+					.optional() };
+	}
+
 	@Configuration(proxyBeanMethods = false)
 	@EnableScheduling
 	@Import(BaseDocumentationConfiguration.class)
@@ -96,7 +123,7 @@ void processOrders() {
 
 		}
 
-		@Scheduled(fixedDelay = 5000, initialDelay = 5000)
+		@Scheduled(fixedDelay = 5000, initialDelay = 0)
 		void purge() {
 
 		}
@@ -108,7 +135,10 @@ void retrieveIssues() {
 
 		@Bean
 		SchedulingConfigurer schedulingConfigurer() {
-			return (registrar) -> registrar.addTriggerTask(new CustomTriggeredRunnable(), new CustomTrigger());
+			return (registrar) -> {
+				registrar.setTaskScheduler(new TestTaskScheduler());
+				registrar.addTriggerTask(new CustomTriggeredRunnable(), new CustomTrigger());
+			};
 		}
 
 		static class CustomTrigger implements Trigger {
@@ -124,7 +154,18 @@ static class CustomTriggeredRunnable implements Runnable {
 
 			@Override
 			public void run() {
+				throw new IllegalStateException("Failed while running custom task");
+			}
+
+		}
+
+		static class TestTaskScheduler extends SimpleAsyncTaskScheduler {
 
+			TestTaskScheduler() {
+				setThreadNamePrefix("test-");
+				// do not log task errors
+				setErrorHandler((throwable) -> {
+				});
 			}
 
 		}