Scheduling a task in Java

Using Spring, scheduling a task is quite simple. Just follow these steps:

1. Write a class that defines the scheduled tasks. Use @Scheduled annotation.

package com.noushin.spring.scheduler;

import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Component;

@Component
public class TaskScheduler {

   // run the task every n seconds, 5 secs = 5000
   @Scheduled(fixedDelayString = "${task.execution.time.delayed}")
   public void delayedTask() {
      System.out.println("Do something meaningful after each delayed period.");
   }

   // run the task every once in a while, example: 0 13 30 * * * means run this task every day at 1:30 pm
   @Scheduled(cron = "${task.execution.time.every.day}")
   public void dailyTask() {
      System.out.println("Do something meaningful once a day.");
   }

}

2. Write a main class to load Spring's application context.

package com.noushin.spring.scheduler;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class SechedulerMain {
   
   static TaskScheduler reportScheduler;
   
   public static void main(String[] args) {
      try {
         ApplicationContext ctx = new ClassPathXmlApplicationContext("application-context.xml");
         if (ctx != null) {
            reportScheduler = ctx.getBean(TaskScheduler.class);
            while (true) {
               System.out.println("main: --------------------------");
               Thread.sleep(1000);
            }          
         }
      }
      catch (Exception ex) {
         System.out.println("SchedulerMain encountered an error and ended.");
         ex.printStackTrace();
      }
   }
}

3. Add application-context.xml.

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

 <!-- Scan components for annotations within the configured package -->
 <context:component-scan base-package="com.noushin.spring" />
 
 <context:property-placeholder location="task.properties" />
       
 <!-- Activate annotation configured components -->
 <context:annotation-config />
 
 <!-- Scheduling tasks using annotations -->
 <task:annotation-driven />

</beans>

4. A property file to configure the scheduler, lets call it task.properties.

# Scheduling report job
task.execution.time.delayed=5000
report.execution.time.every.day=13 30 * * * *

Note: Use the Crontab Patterns as defined in : http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/scheduling/support/CronSequenceGenerator.html

5. Use the following dependencies in your pom.xml:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.noushin.spring</groupId>
    <artifactId>scheduler</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>scheduler</name>
    <description>Demo</description>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <log4j.version>1.2.17</log4j.version>
        <spring.version>4.0.2.RELEASE</spring.version>
    </properties>

    <dependencies>
        <!-- Logging -->
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>${log4j.version}</version>
        </dependency>

        <!-- Spring Context -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>${spring.version}</version>
        </dependency>
    </dependencies>
</project>