scheduling_tasks.md

Scheduling Tasks

1. Scheduling tasks with Spring

Project

1. App that prints current time every 5 seconds using @Scheduled

Starting with Spring Initializr

1. No dependencies

Adding the awaitility Dependency

	<dependency>
		<groupId>org.awaitility</groupId>
		<artifactId>awaitility</artifactId>
		<version>3.1.2</version> <!-- latest version doesn't work for this tutorial -->
		<scope>test</scope>
	</dependency>

Construct a Scheduled Task

1. ScheduledTasks

    @Component
    public class ScheduledTasks {
    	private static final Logger log = LoggerFactory.getLogger(ScheduledTasks.class);
    	
    	private static final SimpleDateFormat dateFormat = new SimpleDateFormat("HH:mm:ss");
    	
    	@Scheduled(fixedRate = 5000)
    	public void reportCurrentTime() {
    		log.info("The time is now {}", dateFormat.format(new Date()));
    	}
    }
   

   1. Scheduled - annotation
      1. It defines when a particular method runs
      2. fixedRate - interval between method invocations (from start time of each invocation)
         1. Other options
            1. fixedDelay - interval from completion of the task
         2. @Scheduled(cron="...") - for more sophistication

Enable Scheduling

1. Main class:

    @SpringBootApplication
    @EnableScheduling // **(M)**
    public class SchedulingTasksApplication {
    	public static void main(String[] args) {
    		SpringApplication.run(SchedulingTasksApplication.class);
    	}
    }
   

   1. @EnableScheduling - Ensures that a background task executor is created (required for scheduling)