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This guide walks you through the steps for scheduling tasks with Spring.
== What You Will Build
You will build an application that prints out the current time every five seconds by using Spring Framework's https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/scheduling/annotation/Scheduled.html[`@Scheduled`^] annotation.
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[[scratch]] == Starting with Spring Initializr
You can use this https://start.spring.io/#!type=gradle-project&language=java&packaging=jar&groupId=com.example&artifactId=scheduling-tasks&name=scheduling-tasks&description=Demo%20project%20for%20Spring%20Boot&packageName=com.example.scheduling-tasks[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:
. Navigate to https://start.spring.io[https://start.spring.io^]. This service pulls in all the dependencies you need for an application and does most of the setup for you. . Choose either Gradle or Maven and the language you want to use. This guide assumes that you chose Java and Gradle. . Click Generate. . Download the resulting ZIP file, which is an archive of an application that is configured with your choices.
NOTE: If your IDE has the Spring Initializr integration, you can complete this process from your IDE.
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== Enable Scheduling
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:
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Spring Initializr adds the @SpringBootApplication annotation to our main class. @SpringBootApplication is a convenience annotation that adds all of the following:
@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 Scheduled Task
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 https://docs.spring.io/spring-framework/reference/integration/scheduling.html#scheduling-annotation-support-scheduled[`Scheduled` annotation^] defines when a particular method runs.
NOTE: This example uses https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/scheduling/annotation/Scheduled.html#fixedRate()[`fixedRate()^], which specifies the interval between method invocations, measured from the start time of each invocation. Other options are https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/scheduling/annotation/Scheduled.html#cron()[cron()^] and https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/scheduling/annotation/Scheduled.html#fixedDelay()[fixedDelay()^]. For periodic tasks, exactly one of these three options must be specified, and optionally, https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/scheduling/annotation/Scheduled.html#initialDelay()[initialDelay()`^]. For a one-time task, it is sufficient to just specify an initialDelay()
== Running the Application
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:
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Doing so starts the application, and the method annotated with @Scheduled runs. You should see log messages similar to:
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NOTE: This example uses https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/scheduling/annotation/Scheduled.html#fixedRate()[`fixedRate()`^] scheduling, so the application runs indefinitely until you interrupt it manually.
== Testing with the awaitility Dependency
To properly test your application, you can use the https://github.com/awaitility/awaitility[`awaitilitylibrary^]. Since Spring Boot 3.2, this is a dependency that Boot manages. You can create a new test or view the existing test atsrc/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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== Summary
Congratulations! You created an application with a scheduled task.
== See Also
The following guides may also be helpful:
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