Spring Task Execution and Scheduling

Original chapter: Task Execution and Scheduling. The text and examples below are preserved from the historical source; read the corrections above before using them.

Section 11.1: Enable Scheduling

Spring provides a useful task scheduling support. To enable it, just annotate any of your @Configuration classes with @EnableScheduling:

Source example · PDF page 50

@Configuration
@EnableScheduling
public class MyConfig {

     // Here it goes your configuration
}

Section 11.2: Cron expression

A Cron expression consists of six sequential fields -

Source example · PDF page 50

second, minute, hour, day of month, month, day(s) of week

and is declared as follows

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@Scheduled(cron = "* * * * * *")

We can also set the timezone as -

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@Scheduled(cron="* * * * * *", zone="Europe/Istanbul")

Notes: -

syntax means example explanation ------------------------------------------------------------------------------------ * match any "* * * * * *" do always */x every x "*/5 * * * * *" do every five seconds ? no specification "0 0 0 25 12 ?" do every Christmas Day

Example: -

syntax means ------------------------------------------------------------------------------------ "0 0 * * * *" the top of every hour of every day. "*/10 * * * * *" every ten seconds. "0 0 8-10 * * *" 8, 9 and 10 o'clock of every day. "0 0/30 8-10 * * *" 8:00, 8:30, 9:00, 9:30 and 10 o'clock every day. "0 0 9-17 * * MON-FRI" on the hour nine-to-five weekdays "0 0 0 25 12 ?" every Christmas Day at midnight

A method declared with @Scheduled() is called explicitly for every matching case.

If we want some code to be executed when a cron expression is met, then we have to specify it in the annotation:

Source example · PDF page 50

@Component
public class MyScheduler{
   @Scheduled(cron="*/5 * * * * MON-FRI")
   public void doSomething() {
        // this will execute on weekdays
   }
}

If we want to print current time in our console for every after 5 seconds -

Source example · PDF page 51

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Component;

import java.text.SimpleDateFormat;
import java.util.Date;

@Component
public class Scheduler {

   private static final Logger log = LoggerFactory.getLogger(Scheduler.class);
   private static final SimpleDateFormat dateFormat = new SimpleDateFormat("HH:mm:ss");

   @Scheduled(cron = "*/5 * * * * *")
   public void currentTime() {
       log.info("Current Time      = {}", dateFormat.format(new Date()));
   }

}

Example using XML configuration:

Example class:

Source example · PDF page 51

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Component;

import java.text.SimpleDateFormat;
import java.util.Date;

@Component("schedulerBean")
public class Scheduler {

   private static final Logger log = LoggerFactory.getLogger(Scheduler.class);
   private static final SimpleDateFormat dateFormat = new SimpleDateFormat("HH:mm:ss");

   public void currentTime() {
       log.info("Current Time      = {}", dateFormat.format(new Date()));
   }

}

Example XML(task-context.xml):

Source example · PDF page 51

 <?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:task="http://www.springframework.org/schema/task"
  xsi:schemaLocation="http://www.springframework.org/schema/beans
      http://www.springframework.org/schema/beans/spring-beans-4.1.xsd
      http://www.springframework.org/schema/task
      http://www.springframework.org/schema/task/spring-task-4.1.xsd">

   <task:scheduled-tasks scheduler="scheduledTasks">
       <task:scheduled ref="schedulerBean" method="currentTime" cron="*/5 * * * * MON-FRI" />
   </task:scheduled-tasks>

   <task:scheduler id="scheduledTasks" />

</beans>

Section 11.3: Fixed delay

If we want some code to be executed periodically after the execution which was before is finished, we should use fixed delay (measured in milliseconds):

Source example · PDF page 52

@Component
public class MyScheduler{

   @Scheduled(fixedDelay=5000)
   public void doSomething() {
        // this will execute periodically, after the one before finishes
   }
}

Section 11.4: Fixed Rate

If we want something to be executed periodically, this code will be triggered once per the value in milliseconds we specify:

Source example · PDF page 52

@Component
public class MyScheduler{

   @Scheduled(fixedRate=5000)
   public void doSomething() {
        // this will execute periodically
   }
}