Lab M06P01

1. Enable scheduling with the @EnableScheduling annotation on Application class

2. Implement a library checker component, which periodically checks number of books in library every 3 seconds. Use the @Scheduled annotation on handler method. This method will be scheduler by Spring task scheduler for execution.

     @Component
     public class LibraryChecker {
       private static final Logger LOG = LoggerFactory.getLogger(LibraryChecker.class);
       private LibraryService libraryService;
   
       public LibraryChecker(LibraryService libraryService) {
         this.libraryService = libraryService;
       }
   
       @Scheduled(initialDelay = 2000, fixedRate = 3000)
       public void check(){
         LOG.info("--- [check] Library contains {} books ---", libraryService.getAllBooks().size());
       }
     } 
   

3. Add test to verify, if scheduler works correctly.

     import org.awaitility.Duration;
     import static org.awaitility.Awaitility.await;
     import static org.mockito.Mockito.atLeast;
     import static org.mockito.Mockito.verify;
   
     @SpringBootTest
     public class LibraryCheckerTest {
   
       @SpyBean
       LibraryChecker libraryChecker;
   
       @Test
       public void checkTest(){
         await().atMost(Duration.TEN_SECONDS).untilAsserted(() -> {
             verify(libraryChecker, atLeast(2)).check();
         });
       }
     }
   

4. You can, configure custom task scheduler bean and use its API for programmatic scheduling.

     @Bean
     public ThreadPoolTaskScheduler threadPoolTaskScheduler(){
         ThreadPoolTaskScheduler threadPoolTaskScheduler = new ThreadPoolTaskScheduler();
         threadPoolTaskScheduler.setPoolSize(10);
         threadPoolTaskScheduler.setThreadNamePrefix("my-scheduler");
         return threadPoolTaskScheduler;
     }  
   

5. Extends the LibraryChecker with method for initialization of a programmatic scheduler. You need to implement Runnable Task.

     @Component
     public class LibraryChecker {
       private static final Logger LOG = LoggerFactory.getLogger(LibraryChecker.class);
   
       private LibraryService libraryService;
       private TaskScheduler threadPoolTaskScheduler;
   
       public LibraryChecker(LibraryService libraryService, TaskScheduler threadPoolTaskScheduler) {
         this.libraryService = libraryService;
         this.threadPoolTaskScheduler = threadPoolTaskScheduler;
       }
   
       public void checkWithScheduler(long rate){
           LOG.info("Scheduling task using task scheduler...");
           threadPoolTaskScheduler.scheduleAtFixedRate(new LibraryTask("checkWithScheduler"), rate);
       }
   
       class LibraryTask implements Runnable{
         private String name;
   
         public LibraryTask(String name){
           this.name = name;
         }
   
         @Override
         public void run() {
           LOG.info("---[{}}] Library contains {} books ---", name, libraryService.getAllBooks().size());
         }
       }
     }
   

6. You can also use Trigger to schedule task.

      public void checkWithSchedulerTrigger(Trigger trigger){
        LOG.info("Scheduling task using triggered task scheduler...");
        threadPoolTaskScheduler.schedule(new LibraryTask("checkWithSchedulerTrigger"), trigger);
      }
   

     // Every 5 seconds
     CronTrigger cronTrigger = new CronTrigger("0/5 * * * * ?");
     libraryChecker.checkWithSchedulerTrigger(cronTrigger);