This guide walks you through the steps for scheduling tasks with Spring.
You will build an application that prints out the current time every five seconds by using
Spring Framework’s @Scheduled annotation.
You can use this pre-initialized project and click Generate to download a ZIP file. This project is configured to fit the examples in this guide.
To manually initialize the project:
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Navigate to https://start.spring.io. This service pulls in all the dependencies you need for an application and does most of the setup for you.
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Choose either Gradle or Maven and the language you want to use. This guide assumes that you chose Java and Gradle.
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Click Generate.
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Download the resulting ZIP file, which is an archive of an application that is configured with your choices.
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Note
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If your IDE has the Spring Initializr integration, you can complete this process from your IDE. |
Although scheduled tasks can be embedded in web applications, the simpler approach (shown in this guide) creates a standalone application. To do so, package everything in a single, executable JAR file, driven by a Java main() method. The following snippet (from src/main/java/com/example/schedulingtasks/SchedulingTasksApplication.java) shows the application class:
@SpringBootApplication
@EnableScheduling
public class SchedulingTasksApplication {Spring Initializr adds the @SpringBootApplication annotation to our main class. @SpringBootApplication is a convenience annotation that adds all of the following:
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@Configuration: Tags the class as a source of bean definitions for the application context. -
@EnableAutoConfiguration: Spring Boot attempts to automatically configure your Spring application based on the dependencies that you have added. -
@ComponentScan: Tells Spring to look for other components, configurations, and services. If specific packages are not defined, recursive scanning begins with the package of the class that declares the annotation.
Additionally, add the @EnableScheduling annotation. This annotation enables Spring’s scheduled task execution capability.
Create a new class src/main/java/com/example/schedulingtasks/ScheduledTasks.java called:
@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()));
}
}The Scheduled annotation defines when a particular method runs.
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Note
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This example uses fixedRate(), which specifies the interval between method
invocations, measured from the start time of each invocation. Other options are cron() and fixedDelay(). For periodic tasks, exactly one of these three options must be specified, and optionally, initialDelay(). For a one-time task, it is sufficient to just specify an initialDelay()
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You should now be able to run the application by executing the main method in SchedulingTasksApplication. You can run the program from your IDE, or by executing the following Gradle command in the project root directory:
./gradlew bootRun
Doing so starts the application, and the method annotated with @Scheduled runs. You should see log messages similar to:
20yy-mm-ddT07:23:01.665-04:00 INFO 19633 --- [ scheduling-1] c.e.schedulingtasks.ScheduledTasks : The time is now 07:23:01 20yy-mm-ddT07:23:06.663-04:00 INFO 19633 --- [ scheduling-1] c.e.schedulingtasks.ScheduledTasks : The time is now 07:23:06 20yy-mm-ddT07:23:11.663-04:00 INFO 19633 --- [ scheduling-1] c.e.schedulingtasks.ScheduledTasks : The time is now 07:23:11
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Note
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This example uses fixedRate() scheduling, so the application runs indefinitely until you interrupt it manually.
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To properly test your application, you can use the awaitility library. Since Spring Boot 3.2, this is a dependency that Boot manages. You can create a new test or view the existing test at src/test/java/com/example/schedulingtasks/ScheduledTasksTest.java:
@SpringBootTest
public class ScheduledTasksTest {
@SpyBean
ScheduledTasks tasks;
@Test
public void reportCurrentTime() {
await().atMost(Durations.TEN_SECONDS).untilAsserted(() -> {
verify(tasks, atLeast(2)).reportCurrentTime();
});
}
}This test automatically runs when you run the ./gradlew clean build task.
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