springboot定时任务（2）

太过爱你忘了你带给我的痛 2022-12-26 02:23 9阅读 0赞

# 前言 #

我们通常在设定了定时任务的频率之后，上线运行之后，有一天我们想要改变这个频率，通常的做法是修改代码，然后发布上线，这对于一个稍微有自我要求的程序员来说显然是不可接受的。那么有没有办法在springboot中实现动态改变这个频率呢，答案显然是有的。此处附上[springboot官方文档][springboot]。

# 策略 #

我们可以把这个频率（比如con表达式）存储在数据库中，然后去读取这个表达式，从而动态的改变频率。我这里使用的是mysql数据库

# 依赖 #

<dependency>
                <groupId>org.mybatis.spring.boot</groupId>
                <artifactId>mybatis-spring-boot-starter</artifactId>
                <version>1.3.1</version>
            </dependency>
            <dependency>
                <groupId>org.mybatis</groupId>
                <artifactId>mybatis</artifactId>
                <version>3.4.5</version>
                <scope>compile</scope>
            </dependency>
            <dependency>
                <groupId>mysql</groupId>
                <artifactId>mysql-connector-java</artifactId>
            </dependency>

# 数据库设计 #

CREATE TABLE `cron` (
      `id` int primary key auto_increment,
      `cron` varchar(30) NOT NULL,
    ) ENGINE=InnoDB DEFAULT CHARSET=utf8;

插入两条数据  
![image.png][]

*  第一条数据用来实现动态cron表达式的方式
 *  第二条数据用来实现固定间隔周期的方式

# 代码部分 #

package cn.juhe;
    
    import org.apache.ibatis.annotations.Mapper;
    import org.apache.ibatis.annotations.Select;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.context.annotation.Configuration;
    import org.springframework.scheduling.Trigger;
    import org.springframework.scheduling.TriggerContext;
    import org.springframework.scheduling.annotation.EnableScheduling;
    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.util.StringUtils;
    
    import java.time.LocalDateTime;
    import java.util.Date;
    import java.util.concurrent.TimeUnit;
    
    /**
     * @Author: micro cloud fly
     * @Description: 可以动态的从数据库修改定时任务的crontab表达式
     * @Date: Created in 2:10 下午 2020/11/25
     */
    @Configuration
    @EnableScheduling
    public class DynamicScheduleTask implements SchedulingConfigurer {
    
        @Mapper
        public interface CronMapper {
            @Select("select cron from cron where id=2")
            public String getCron();
        }
    
        @Autowired      //注入mapper
        @SuppressWarnings("all")
        CronMapper cronMapper;
    
        /**
         * 配置定时任务.
         */
        @Override
        public void configureTasks(ScheduledTaskRegistrar taskRegistrar) {
    
            taskRegistrar.addTriggerTask(
                    //1.第一个参数是一个实现Runnable接口的实现类
                    new MyTask(),
                    //2.第二个参数是一个trigger，trigge是一个接口，里面只有一个方法，就是返回一个Date
    //                new MyCronTrigger()
                    new MyPeriodicTrigger()
            );
        }
    
        /**
         * cron表达式的实现方式
         */
        private class MyCronTrigger implements Trigger{
    
            @Override
            public Date nextExecutionTime(TriggerContext triggerContext) {
                return new CronTrigger(cronMapper.getCron()).nextExecutionTime(triggerContext);
            }
        }
    
        /**
         * 固定频率的实现方式
         */
        private  class MyPeriodicTrigger implements Trigger{
    
            @Override
            public Date nextExecutionTime(TriggerContext triggerContext) {
                return new PeriodicTrigger(Long.parseLong(cronMapper.getCron()), TimeUnit.MILLISECONDS).nextExecutionTime(triggerContext);
            }
        }
    
        /**
         * 自身的业务实现类
         */
        private class MyTask implements Runnable{
    
            @Override
            public void run() {
                System.out.println("开始执行我的定时任务: " + LocalDateTime.now());
            }
        }
    
    }

# 补充 #

通过源码可以发现，Trigger接口有两个默认的实现  
![image.png][image.png 1]  
因此，我的代码里面实现了两种方式。

# 附录，spring官方文档 #

@Target(value=TYPE)
     @Retention(value=RUNTIME)
     @Import(value=SchedulingConfiguration.class)
     @Documented
    public @interface EnableScheduling

Enables Spring’s scheduled task execution capability, similar to functionality found in Spring’s [task:\*][task] XML namespace. To be used on @Configuration classes as follows:

@Configuration
     @EnableScheduling
     public class AppConfig {
    
         // various @Bean definitions
     }

This enables detection of `@Scheduled`annotations on any Spring-managed bean in the container. For example, given a class MyTask

package com.myco.tasks;
    
     public class MyTask {
    
         @Scheduled(fixedRate=1000)
         public void work() {
             // task execution logic
         }
     }

the following configuration would ensure that`MyTask.work()` is called once every 1000 ms:

@Configuration
     @EnableScheduling
     public class AppConfig {
    
         @Bean
         public MyTask task() {
             return new MyTask();
         }
     }

Alternatively, if MyTask were annotated with `@Component` , the following configuration would ensure that its `@Scheduled` method is invoked at the desired interval:

@Configuration
     @EnableScheduling
     @ComponentScan(basePackages="com.myco.tasks")
     public class AppConfig {
     }

Methods annotated with `@Scheduled` may even be declared directly within  
`@Configuration`classes:

@Configuration
     @EnableScheduling
     public class AppConfig {
    
         @Scheduled(fixedRate=1000)
         public void work() {
             // task execution logic
         }
     }

By default, will be searching for an associated scheduler definition: either a unique TaskScheduler bean in the context, or a TaskScheduler bean named “taskScheduler” otherwise; the same lookup will also be performed for a ScheduledExecutorService bean. If neither of the two is resolvable, a local single-threaded default scheduler will be created and used within the registrar.

When more control is desired, a `@Configuration`class may implement SchedulingConfigurer. This allows access to the underlying ScheduledTaskRegistrar instance. For example, the following example demonstrates how to customize the Executor used to execute scheduled tasks:

@Configuration
     @EnableScheduling
     public class AppConfig implements SchedulingConfigurer {
    
         @Override
         public void configureTasks(ScheduledTaskRegistrar taskRegistrar) {
             taskRegistrar.setScheduler(taskExecutor());
         }
    
         @Bean(destroyMethod="shutdown")
         public Executor taskExecutor() {
             return Executors.newScheduledThreadPool(100);
         }
     }

Note in the example above the use of @Bean(destroyMethod=“shutdown”). This ensures that the task executor is properly shut down when the Spring application context itself is closed.

Implementing SchedulingConfigurer also allows for fine-grained control over task registration via the ScheduledTaskRegistrar. For example, the following configures the execution of a particular bean method per a custom Trigger implementation:

@Configuration
     @EnableScheduling
     public class AppConfig implements SchedulingConfigurer {
    
         @Override
         public void configureTasks(ScheduledTaskRegistrar taskRegistrar) {
             taskRegistrar.setScheduler(taskScheduler());
             taskRegistrar.addTriggerTask(
                 new Runnable() {
                     public void run() {
                         myTask().work();
                     }
                 },
                 new CustomTrigger()
             );
         }
    
         @Bean(destroyMethod="shutdown")
         public Executor taskScheduler() {
             return Executors.newScheduledThreadPool(42);
         }
    
         @Bean
         public MyTask myTask() {
             return new MyTask();
         }
     }

[springboot]: https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/scheduling/annotation/EnableScheduling.html
[image.png]: /images/20221120/2ccf4b46de804fdda6e63797a474b6a0.png
[image.png 1]: /images/20221120/d27ba7451dde4751b23e572441626221.png
[task]: https://www.sdk.cn/details/Z253zkRawlrA8a0eAm