Spring Scheduling & Async

Full Reference: See async.md for async configuration, multiple executors, and CompletableFuture patterns. Full Reference: See distributed.md for ShedLock, error handling, dynamic scheduling, and testing.

Quick Start

@SpringBootApplication
@EnableScheduling
@EnableAsync
public class Application {}

@Service
@Slf4j
public class ScheduledTasks {

    @Scheduled(fixedRate = 60000)  // Every minute
    public void runEveryMinute() {
        log.info("Task executed at {}", LocalDateTime.now());
    }

    @Async
    public CompletableFuture<String> asyncOperation() {
        return CompletableFuture.completedFuture("Done");
    }
}

---

@Scheduled

Fixed Rate vs Fixed Delay

@Service
public class ScheduledTasks {

    // Fixed Rate: runs every 5s from start of previous
    @Scheduled(fixedRate = 5000)
    public void fixedRateTask() { }

    // Fixed Delay: runs 5s after previous completes
    @Scheduled(fixedDelay = 5000)
    public void fixedDelayTask() { }

    // Initial delay before first run
    @Scheduled(fixedRate = 5000, initialDelay = 10000)
    public void delayedStart() { }

    // Configurable via properties
    @Scheduled(fixedRateString = "${task.rate:5000}")
    public void configurableTask() { }

    // With TimeUnit
    @Scheduled(fixedRate = 1, timeUnit = TimeUnit.MINUTES)
    public void everyMinute() { }
}

Cron Expressions

@Service
public class CronTasks {

    // Daily at 2:00 AM
    @Scheduled(cron = "0 0 2 * * *")
    public void dailyAt2AM() { }

    // Every Monday at 9:00 AM
    @Scheduled(cron = "0 0 9 * * MON")
    public void everyMondayAt9AM() { }

    // Every 15 minutes during business hours (9-18)
    @Scheduled(cron = "0 */15 9-18 * * MON-FRI")
    public void businessHoursTask() { }

    // With timezone
    @Scheduled(cron = "0 0 9 * * *", zone = "Europe/Rome")
    public void dailyAt9AMRome() { }

    // Disable with "-"
    @Scheduled(cron = "${task.cron:-}")
    public void optionalTask() { }
}

Cron Expression Reference

┌───────────── second (0-59)
│ ┌───────────── minute (0-59)
│ │ ┌───────────── hour (0-23)
│ │ │ ┌───────────── day of month (1-31)
│ │ │ │ ┌───────────── month (1-12 or JAN-DEC)
│ │ │ │ │ ┌───────────── day of week (0-7 or SUN-SAT)
│ │ │ │ │ │
* * * * * *

Expression	Description
0 0 * * * *	Every hour
0 */10 * * * *	Every 10 minutes
0 0 8-18 * * *	Every hour from 8 AM to 6 PM
0 0 9 * * MON-FRI	9 AM on weekdays
0 0 0 1 * *	First day of every month

---

@Async

Basic Configuration

@Configuration
@EnableAsync
public class AsyncConfig implements AsyncConfigurer {

    @Override
    @Bean(name = "taskExecutor")
    public Executor getAsyncExecutor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(5);
        executor.setMaxPoolSize(10);
        executor.setQueueCapacity(100);
        executor.setThreadNamePrefix("Async-");
        executor.setRejectedExecutionHandler(new ThreadPoolExecutor.CallerRunsPolicy());
        executor.setWaitForTasksToCompleteOnShutdown(true);
        executor.setAwaitTerminationSeconds(60);
        executor.initialize();
        return executor;
    }
}

Async Methods

@Service
public class AsyncService {

    // Fire and forget
    @Async
    public void sendEmailAsync(String to, String subject, String body) {
        emailSender.send(to, subject, body);
    }

    // With result
    @Async
    public CompletableFuture<Report> generateReportAsync(ReportRequest request) {
        Report report = reportGenerator.generate(request);
        return CompletableFuture.completedFuture(report);
    }

    // With specific executor
    @Async("reportExecutor")
    public CompletableFuture<Report> generateHeavyReport(ReportRequest request) {
        return CompletableFuture.completedFuture(reportGenerator.generateHeavy(request));
    }
}

---

Task Executor Configuration

spring:
  task:
    execution:
      pool:
        core-size: 5
        max-size: 10
        queue-capacity: 100
        keep-alive: 60s
      thread-name-prefix: task-
      shutdown:
        await-termination: true
        await-termination-period: 60s

    scheduling:
      pool:
        size: 3
      thread-name-prefix: scheduling-

---

Best Practices

Do	Don't
Use ShedLock for clustered env	Allow duplicate executions
Configure error handler	Ignore task exceptions
Monitor execution time	Deploy without metrics
Use CompletableFuture for results	Use void async without handler
Configure graceful shutdown	Kill running tasks abruptly

Production Checklist

• @EnableScheduling and @EnableAsync configured
• Thread pool properly sized
• ShedLock for clustered environment
• Error handling implemented
• Metrics for monitoring
• Graceful shutdown configured
• Retry for transient failures

Anti-Patterns

Anti-Pattern	Problem	Solution
Missing @EnableScheduling	Task doesn't run	Add annotation
Internal @Async call	Proxy bypassed	Use self-injection
Task overlap	Concurrent execution	Use fixed delay or ShedLock
Small thread pool	Thread starvation	Size pool appropriately
Void async without handler	Lost exceptions	Implement AsyncUncaughtExceptionHandler

Quick Troubleshooting

Problem	Diagnostic	Fix
Task not executing	Check annotations	Add @EnableScheduling
Async not working	Check call site	Avoid internal calls
Task runs multiple times	Check cluster	Add ShedLock
Thread pool exhausted	Check pool config	Increase pool size

Reference Documentation

• Task Execution and Scheduling
• ShedLock