Scheduling tasks with Spring (updated)

Spring provides an easy way to schedule tasks.

Let's say that we would like to have an information about current time printed on a console periodically.

The class that prints the time may look like this:

	public class TimePrinter {
	private static final SimpleDateFormat DATE_FORMAT = new SimpleDateFormat("HH:mm:ss");
	private static final Logger LOGGER = LoggerFactory.getLogger(TimePrinter.class.getName());
	public void reportCurrentTime() {
	LOGGER.info("The time is now " + DATE_FORMAT.format(new Date()));
	}
	}

view raw TimePrinter.java hosted with ❤ by GitHub

We need to define a class that will encapsulate the printing task:

	public class ScheduledTask {
	static final String THREAD_NAME = ScheduledTask.class.getName() + "!";
	@Autowired private TimePrinter timePrinter;
	@Scheduled(fixedRate = 5000)
	public void reportCurrentTime() {
	Thread.currentThread().setName(THREAD_NAME);
	timePrinter.printCurrentTime();
	}
	}

view raw ScheduledTask.java hosted with ❤ by GitHub

The @Scheduled annotation is the key here: the method reportCurrentTime is annotated by it, therefore it will be invoked every 5 seconds.
You can also specify cron expression. You can use fixedRateString parameter if you want to read it from properties file.
Please note setting of the thread name - it will be needed for the test.
Adding production code only for tests is generally not a good practice, but in this case it can also be used for monitoring purposes.

The spring configuration looks as following:

	@Configuration
	@EnableScheduling
	@ComponentScan("pl.mjedynak")
	public class AppConfig {
	@Bean
	public ScheduledTask scheduledTask() {
	return new ScheduledTask();
	}
	@Bean
	public TimePrinter timePrinter() {
	return new TimePrinter();
	}
	}

view raw AppConfig.java hosted with ❤ by GitHub

To run it we need to create an invoker class:

	public class App {
	public static void main(String[] args) {
	new AnnotationConfigApplicationContext(AppConfig.class);
	}
	}

view raw App.java hosted with ❤ by GitHub

Unfortunately there is no trivial way to test it automatically. We can do it the following way.
Let's create a test class:

	@RunWith(SpringJUnit4ClassRunner.class)
	@ContextConfiguration(classes = AppConfig.class)
	public class ScheduledTaskIntegrationTest {
	@Test
	public void shouldInvokeTask() {
	Callable<Boolean> threadWithNameExists =
	() -> getAllStackTraces().keySet().stream().
	anyMatch(t -> t.getName().equals(ScheduledTask.THREAD_NAME));
	await().until(threadWithNameExists, is(true));
	}
	}

view raw ScheduledTaskIntegrationTest.java hosted with ❤ by GitHub

When we run the test, the spring context will start and the task will be invoked by scheduler.
We check if the thread with our name exists.
We do it for some time to avoid race condition - it may happen that verification method will be invoked before thread starts.
The whole project alongside with dependencies can be found on github.