Earlier in this chapter, we discussed how the command-line runners can be used as a place to start the scheduled executor thread pools in order to run the worker threads in intervals. While that is certainly a possibility, Spring provides you with a more concise configuration to achieve the same goal: @EnableScheduling.
We will enhance our application so that it will print a count of books in our repository every 10 seconds. To achieve this, we will make the necessary modifications to the BookPubApplication and StartupRunner classes.
Let's add an
@EnableSchedulingannotation to theBookPubApplicationclass, as follows:@SpringBootApplication @EnableScheduling public class BookPubApplication {…}As an
@Scheduledannotation can be placed only on methods without arguments, let's add a newrun()method to theStartupRunnerclass and annotate it with the@Scheduledannotation, as shown in the following line:@Scheduled(initialDelay = 1000, fixedRate = 10000) public void run() { logger.info("Number of books: " + bookRepository.count()); }Start the application by executing
./gradlew clean bootRunfrom the command line so as to observe theNumber of books: 0message that shows in the logs every 10 seconds.
Like some other annotations that we discussed in this chapter and will further discuss in the book, @EnableScheduling is not a Spring Boot annotation, but instead is a Spring Context module annotation. Similar to the @SpringBootApplication and @EnableAutoConfiguration annotations, this is a meta-annotation and internally imports the SchedulingConfiguration via the @Import(SchedulingConfiguration.class) instruction, which can be seen if looked found inside the code for the @EnableScheduling annotation class.
ScheduledAnnotationBeanPostProcessor that will be created by the imported configuration will scan the declared Spring Beans for the presence of the @Scheduled annotations. For every annotated method without arguments, the appropriate executor thread pool will be created. It will manage the scheduled invocation of the annotated method.