Implementing Dynamic Scheduled Tasks in Spring Boot

Previously I wrote about using static scheduled tasks in a Spring Boot project with cron expressions defined in configuration files, which cannot be changed while the application is running; this approach is inflexible.

After researching online, I documented how to implement dynamic scheduled tasks in Spring Boot.

Because this is a demo, only the necessary dependencies are added:

<dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
 
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-log4j2</artifactId>
            <optional>true</optional>
        </dependency>
 
        <!-- spring boot 2.3+ requires explicit validation dependency if needed -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-validation</artifactId>
        </dependency>
 
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
    </dependencies>

The main application class enables scheduling:

package com.wl.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.scheduling.annotation.EnableScheduling;

/**
 * @author wl
 * @date 2022/3/22
 */
@EnableScheduling
@SpringBootApplication
public class DemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
        System.out.println("(*^▽^*)启动成功!!!(〃'▽'〃)");
    }
}

The application.yml only defines the server port:

server:
  port: 8089

The task execution time is configured in task-config.ini :

printTime.cron=0/10 * * * * ?

The scheduled task class reads the cron expression from the property file and uses a CronTrigger to schedule the job dynamically:

package com.wl.demo.task;

import lombok.Data;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.PropertySource;
import org.springframework.scheduling.Trigger;
import org.springframework.scheduling.TriggerContext;
import org.springframework.scheduling.annotation.SchedulingConfigurer;
import org.springframework.scheduling.config.ScheduledTaskRegistrar;
import org.springframework.scheduling.support.CronTrigger;
import org.springframework.stereotype.Component;

import java.time.LocalDateTime;
import java.util.Date;

/**
 * 定时任务
 * @author wl
 * @date 2022/3/22
 */
@Data
@Slf4j
@Component
@PropertySource("classpath:/task-config.ini")
public class ScheduleTask implements SchedulingConfigurer {

    @Value("${printTime.cron}")
    private String cron;

    @Override
    public void configureTasks(ScheduledTaskRegistrar taskRegistrar) {
        // 动态使用cron表达式设置循环间隔
        taskRegistrar.addTriggerTask(new Runnable() {
            @Override
            public void run() {
                log.info("Current time： {}", LocalDateTime.now());
            }
        }, new Trigger() {
            @Override
            public Date nextExecutionTime(TriggerContext triggerContext) {
                // 使用CronTrigger触发器，可动态修改cron表达式来操作循环规则
                CronTrigger cronTrigger = new CronTrigger(cron);
                Date nextExecutionTime = cronTrigger.nextExecutionTime(triggerContext);
                return nextExecutionTime;
            }
        });
    }
}

A simple REST controller provides an endpoint to update the cron expression at runtime:

package com.wl.demo.controller;

import com.wl.demo.task.ScheduleTask;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

/**
 * @author wl
 * @date 2022/3/22
 */
@Slf4j
@RestController
@RequestMapping("/test")
public class TestController {

    private final ScheduleTask scheduleTask;

    @Autowired
    public TestController(ScheduleTask scheduleTask) {
        this.scheduleTask = scheduleTask;
    }

    @GetMapping("/updateCron")
    public String updateCron(String cron) {
        log.info("new cron :{}", cron);
        scheduleTask.setCron(cron);
        return "ok";
    }
}

Running the application shows the task executing every 10 seconds. By calling /test/updateCron?cron=0/15 * * * * ? , the interval changes to 15 seconds, which is reflected in the logs.

Besides the cron‑based approach, a PeriodicTrigger can be used for arbitrary millisecond intervals, overcoming the limitation that cron expressions cannot define intervals greater than 59 seconds. The following version of the task class demonstrates this alternative:

package com.wl.demo.task;

import lombok.Data;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.PropertySource;
import org.springframework.scheduling.Trigger;
import org.springframework.scheduling.TriggerContext;
import org.springframework.scheduling.annotation.SchedulingConfigurer;
import org.springframework.scheduling.config.ScheduledTaskRegistrar;
import org.springframework.scheduling.support.CronTrigger;
import org.springframework.scheduling.support.PeriodicTrigger;
import org.springframework.stereotype.Component;

import java.time.LocalDateTime;
import java.util.Date;

/**
 * 定时任务
 * @author wl
 * @date 2022/3/22
 */
@Data
@Slf4j
@Component
@PropertySource("classpath:/task-config.ini")
public class ScheduleTask implements SchedulingConfigurer {

    @Value("${printTime.cron}")
    private String cron;

    private Long timer = 10000L;

    @Override
    public void configureTasks(ScheduledTaskRegistrar taskRegistrar) {
        // 动态使用cron表达式设置循环间隔
        taskRegistrar.addTriggerTask(new Runnable() {
            @Override
            public void run() {
                log.info("Current time： {}", LocalDateTime.now());
            }
        }, new Trigger() {
            @Override
            public Date nextExecutionTime(TriggerContext triggerContext) {
                // 使用CronTrigger触发器，可动态修改cron表达式来操作循环规则
                // CronTrigger cronTrigger = new CronTrigger(cron);
                // Date nextExecutionTime = cronTrigger.nextExecutionTime(triggerContext);

                // 使用PeriodicTrigger实现任意毫秒间隔的循环
                PeriodicTrigger periodicTrigger = new PeriodicTrigger(timer);
                Date nextExecutionTime = periodicTrigger.nextExecutionTime(triggerContext);
                return nextExecutionTime;
            }
        });
    }
}

An additional endpoint allows updating the timer value at runtime:

package com.wl.demo.controller;

import com.wl.demo.task.ScheduleTask;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

/**
 * @author wl
 * @date 2022/3/22
 */
@Slf4j
@RestController
@RequestMapping("/test")
public class TestController {

    private final ScheduleTask scheduleTask;

    @Autowired
    public TestController(ScheduleTask scheduleTask) {
        this.scheduleTask = scheduleTask;
    }

    @GetMapping("/updateCron")
    public String updateCron(String cron) {
        log.info("new cron :{}", cron);
        scheduleTask.setCron(cron);
        return "ok";
    }

    @GetMapping("/updateTimer")
    public String updateTimer(Long timer) {
        log.info("new timer :{}", timer);
        scheduleTask.setTimer(timer);
        return "ok";
    }
}

Testing the new endpoints confirms that the task interval can be changed both via cron expressions and via direct millisecond timers, providing a flexible solution for dynamic scheduling in Spring Boot applications.