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’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 tutorial.
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.
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Click Generate.
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Download the resulting ZIP file, which is an archive of a web 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. |
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Note
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You can also fork the project from Github and open it in your IDE or other editor. |
The tests in
complete/src/test/java/com/example/schedulingtasks/ScheduledTasksTest.java
require the awaitility library.
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Note
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Later versions of the awaitility library do not work for this test, so you have to
specify version 3.1.2.
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To add the awaitility library to Maven, add the following dependency:
<dependency>
<groupId>org.awaitility</groupId>
<artifactId>awaitility</artifactId>
<version>3.1.2</version>
<scope>test</scope>
</dependency>The following listing shows the finished pom.xml file:
link:complete/pom.xml[role=include]To add the awaitility library to Gradle, add the following dependency:
testImplementation 'org.awaitility:awaitility:3.1.2'The following listing shows the finished build.gradle file:
link:complete/build.gradle[role=include]Now that you have set up your project, you can create a scheduled task. The following
listing (from src/main/java/com/example/schedulingtasks/ScheduledTasks.java) shows how
to do so:
link:complete/src/main/java/com/example/schedulingtasks/ScheduledTasks.java[role=include]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. There are
other options,
such as fixedDelay, which specifies the interval between invocations measured from the
completion of the task. You can also use @Scheduled(cron=". . .")
expressions for more sophisticated task scheduling.
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Although scheduled tasks can be embedded in web applications and WAR files, the simpler
approach (shown in the next listing) creates a standalone application. To do so,
package everything in a single, executable JAR file, driven by a good old Java main()
method. The following listing (from
src/main/java/com/example/schedulingtasks/SchedulingTasksApplication.java) shows the
application class:
link:complete/src/main/java/com/example/schedulingtasks/SchedulingTasksApplication.java[role=include]The
@EnableScheduling
annotation ensures that a background task executor is created. Without it, nothing gets
scheduled.
Logging output is displayed, and you can see from the logs that it is on a background thread. You should see your scheduled task fire every five seconds. The following listing shows typical output:
...
2019-10-02 12:07:35.659 INFO 28617 --- [ scheduling-1] c.e.schedulingtasks.ScheduledTasks : The time is now 12:07:35
2019-10-02 12:07:40.659 INFO 28617 --- [ scheduling-1] c.e.schedulingtasks.ScheduledTasks : The time is now 12:07:40
2019-10-02 12:07:45.659 INFO 28617 --- [ scheduling-1] c.e.schedulingtasks.ScheduledTasks : The time is now 12:07:45
2019-10-02 12:07:50.657 INFO 28617 --- [ scheduling-1] c.e.schedulingtasks.ScheduledTasks : The time is now 12:07:50
...Congratulations! You created an application with a scheduled task. Also, this technique works in any type of application.
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