Spring provides annotation support for scheduling method execution using @Scheduled and @EnableScheduling.
Simple use of @Scheduled and @EnableScheduling
Annotate the configuration class with @EnableScheduling
@EnableScheduling
@Configuration
public class MyConfig {
@Bean
public MyBean myBean () {
return new MyBean();
}
}
Use @Scheduled on bean's methods:
public class MyBean {
@Scheduled(fixedRate = 1000)
public void runTask () {
System.out.printf("Running scheduled task " +
" thread: %s, time: %s%n",
Thread.currentThread().getName(),
LocalTime.now());
try {
Thread.sleep(500);
} catch (InterruptedException e) {
}
}
}
Calling @Scheduled method from main method:
public class ScheduledExample {
public static void main (String[] args) throws InterruptedException {
AnnotationConfigApplicationContext context =
new AnnotationConfigApplicationContext(
MyConfig.class);
MyBean bean = context.getBean(MyBean.class);
System.out.printf("calling MyBean#runTask() thread: %s%n",
Thread.currentThread().getName());
bean.runTask();
System.out.println("call MyBean#runTask() returned");
//exit after 5 secs
Thread.sleep(5000);
System.exit(0);
}
}
Output
calling MyBean#runTask() thread: main
Running scheduled task thread: pool-1-thread-1, time: 22:15:07.996
Running scheduled task thread: main, time: 22:15:07.997
call MyBean#runTask() returned
Running scheduled task thread: pool-1-thread-1, time: 22:15:08.984
Running scheduled task thread: pool-1-thread-1, time: 22:15:09.984
Running scheduled task thread: pool-1-thread-1, time: 22:15:10.985
Running scheduled task thread: pool-1-thread-1, time: 22:15:11.985
Running scheduled task thread: pool-1-thread-1, time: 22:15:12.984
Using TaskScheduler other than default:
To specify a custom TaskScheduler we just need to configure it as a bean:
@EnableScheduling
@Configuration
public class MyConfig {
@Bean
public MyBean myBean () {
return new MyBean();
}
@Bean
public TaskScheduler taskExecutor () {
return new ConcurrentTaskScheduler(
Executors.newScheduledThreadPool(3));
}
}
public class MyBean {
@Scheduled(fixedDelay = 1000)
public void runTask () {
System.out.printf("task thread: %s, time: %s%n",
Thread.currentThread().getName(),
LocalTime.now());
try {
Thread.sleep(500);
} catch (InterruptedException e) {
}
}
}
public class ScheduledOverrideDefaultExecutorExample {
public static void main (String[] args) throws Exception {
AnnotationConfigApplicationContext context =
new AnnotationConfigApplicationContext(
MyConfig.class);
MyBean bean = context.getBean(MyBean.class);
bean.runTask();
System.out.println("call MyBean#runTask() returned");
Thread.sleep(3000);
System.out.println("Shutting down after 3 secs");
ConcurrentTaskExecutor exec =
(ConcurrentTaskExecutor) context.getBean("taskExecutor");
ExecutorService es = (ExecutorService) exec.getConcurrentExecutor();
es.shutdownNow();
}
}
task thread: main, time: 22:37:25.202
task thread: pool-1-thread-1, time: 22:37:25.202
call MyBean#runTask() returned
task thread: pool-1-thread-1, time: 22:37:26.742
task thread: pool-1-thread-2, time: 22:37:28.244
Shutting down after 3 secs
@Scheduled method arguments and return value
The methods annotated with @Scheduled must have void returns and must not have any arguments. This is because of it's periodic nature where passing an argument or receiving a return value won't make much sense.
Following example shows that violating this rules will end up with an exception.
@EnableScheduling
@Configuration
public class MyConfig {
@Bean
public MyBean myBean () {
return new MyBean();
}
}
public class MyBean {
@Scheduled
public String runTask (String message) {
System.out.printf("task thread: %s, time: %s%n",
Thread.currentThread().getName(),
LocalTime.now());
System.out.printf("message: %s%n", message);
try {
Thread.sleep(500);
} catch (InterruptedException e) {
}
return "return value";
}
}
public class ScheduledMethodArgExample {
public static void main (String[] args) {
AnnotationConfigApplicationContext context =
new AnnotationConfigApplicationContext(
MyConfig.class);
MyBean bean = context.getBean(MyBean.class);
System.out.printf("calling MyBean#runTask() thread: %s%n",
Thread.currentThread().getName());
String s = bean.runTask("from main");
System.out.println("call MyBean#runTask() returned");
System.out.println("returned value: " + s);
}
}
Output
Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'myBean' defined in com.logicbig.example.ScheduledMethodArgExample$MyConfig: Initialization of bean failed; nested exception is java.lang.IllegalStateException: Encountered invalid @Scheduled method 'runTask': Only no-arg methods may be annotated with @Scheduled
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:562)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:482)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:754)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:866)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:542)
at org.springframework.context.annotation.AnnotationConfigApplicationContext.
(AnnotationConfigApplicationContext.java:84)
at com.logicbig.example.ScheduledMethodArgExample.main(ScheduledMethodArgExample.java:14)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)
Caused by: java.lang.IllegalStateException: Encountered invalid @Scheduled method 'runTask': Only no-arg methods may be annotated with @Scheduled
at org.springframework.scheduling.annotation.ScheduledAnnotationBeanPostProcessor.processScheduled(ScheduledAnnotationBeanPostProcessor.java:413)
at org.springframework.scheduling.annotation.ScheduledAnnotationBeanPostProcessor.postProcessAfterInitialization(ScheduledAnnotationBeanPostProcessor.java:283)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsAfterInitialization(AbstractAutowireCapableBeanFactory.java:422)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1588)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:553)
... 15 more
Using SchedulingConfigurer
The interface SchedulingConfigurer can be implemented by @Configuration classes to provide scheduled tasks without using @Scheduled annotation on beans but still on a JavaConfig level:
@EnableScheduling
@Configuration
public class MyConfig implements SchedulingConfigurer {
@Override
public void configureTasks (ScheduledTaskRegistrar taskRegistrar) {
taskRegistrar.addFixedDelayTask(() -> {
System.out.println("Running task : "+LocalTime.now());
}, 500);
}
}
public class SchedulingConfigurerExample {
public static void main (String[] args) throws InterruptedException {
AnnotationConfigApplicationContext context =
new AnnotationConfigApplicationContext(
MyConfig.class);
Thread.sleep(5000);
System.out.println(" -- Exiting application after 5 sec -- ");
System.exit(0);
}
}
Output
Running task : 23:21:34.588
Running task : 23:21:35.093
Running task : 23:21:35.594
Running task : 23:21:36.094
Running task : 23:21:36.595
Running task : 23:21:37.096
Running task : 23:21:37.598
Running task : 23:21:38.099
Running task : 23:21:38.600
Running task : 23:21:39.101
-- Exiting application after 5 secs--
Using SchedulingConfigurer is necessary when implementing Trigger-based tasks, which are not supported by the @Scheduled annotation.
Cron and other scheduling configuration
@Scheduled annotation allows various configurations elements to allow us different ways to schedule tasks, which includes cron expression, scheduling frequency and initial delay etc. Please check out @Scheduled API doc.
Example ProjectDependencies and Technologies Used: - Spring Context 4.3.4.RELEASE: Spring Context.
- JDK 1.8
- Maven 3.3.9
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