How to Dynamically Change Spring Boot Scheduled Tasks at Runtime

Previously I wrote about using static cron expressions for scheduled tasks in Spring Boot, which required predefined configuration and couldn't be changed at runtime. This article demonstrates how to implement dynamic scheduling by reading the cron expression from an external file and updating it via a REST endpoint.

<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+ needs explicit validation dependency -->
    <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>

Application entry class with @EnableScheduling and @SpringBootApplication.

package com.wl.demo;

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

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

Define a configuration file task-config.ini containing the cron expression. printTime.cron=0/10 * * * * ? Create a task class implementing SchedulingConfigurer, injecting the cron value with @Value, and registering a trigger task that uses CronTrigger to compute the next execution time.

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;

@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) {
        taskRegistrar.addTriggerTask(new Runnable() {
            @Override
            public void run() {
                log.info("Current time： {}", LocalDateTime.now());
            }
        }, new Trigger() {
            @Override
            public Date nextExecutionTime(TriggerContext triggerContext) {
                CronTrigger cronTrigger = new CronTrigger(cron);
                return cronTrigger.nextExecutionTime(triggerContext);
            }
        });
    }
}

Add a REST controller with an endpoint /test/updateCron that receives a new cron expression and updates the task's cron field.

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;

@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.

Calling the endpoint with a new cron expression changes the interval to 15 seconds, as shown in the following screenshots.

Besides cron, a PeriodicTrigger can be used to set arbitrary millisecond intervals, allowing intervals longer than 59 seconds. The task class is updated to include a timer field and a new endpoint /test/updateTimer to modify it.

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.PeriodicTrigger;
import org.springframework.stereotype.Component;
import java.time.LocalDateTime;
import java.util.Date;

@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) {
        taskRegistrar.addTriggerTask(new Runnable() {
            @Override
            public void run() {
                log.info("Current time： {}", LocalDateTime.now());
            }
        }, new Trigger() {
            @Override
            public Date nextExecutionTime(TriggerContext triggerContext) {
                PeriodicTrigger periodicTrigger = new PeriodicTrigger(timer);
                return periodicTrigger.nextExecutionTime(triggerContext);
            }
        });
    }
}

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;

@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 confirms the task now runs with the new timer value.