java分布式系统定时任务，如何保证多台服务只执行一次

超、凢脫俗 2022-06-08 13:09 846阅读 0赞

**思路：**让定时任务执行时，随机睡几秒钟，首先执行的服务器更新job开关，执行完毕后关闭开关

**注意：**个人设计思路，仅供参考哈

一、代码

private static String serverIp = null;
    
        static {
            //获取服务器的IP地址，便于后续追踪
            try {
                InetAddress address = InetAddress.getLocalHost();
                serverIp = address.getHostAddress();
            } catch (Exception e) {
                logger.error("获取服务器IP地址有误！！");
                e.printStackTrace();
            }
        }
    
        /**
         * 每日凌晨1点执行
         */
        @Scheduled(cron = "0 0 1 * * ?")
        public void xxxSchedule(){
            logger.info("job start");
            String jobName = "xxx";
            long startTime = new Date().getTime();
            try {
                if (canExecute(jobName)){
                    jobMapper.xxxSchedule();
                    jobMapper.updateJobStatus(jobName,serverIp,"off");
                    logger.info(jobName+"执行完成，耗时:"+(new Date().getTime()-startTime)+"毫秒！");
                }
            } catch (Exception e) { 
                e.printStackTrace(); 
            }
        }
    
    
        private Boolean canExecute(String jobName) throws Exception {
            int max = 10000;
            int min = (int) Math.round(Math.random()*8000);
            long sleepTime = Math.round(Math.random()*(max-min));
            logger.info(jobName+"睡了："+ sleepTime + "毫秒");
            Thread.sleep(sleepTime);
    
            if (jobMapper.getJobOff(jobName) == 1){
                jobMapper.updateJobStatus(jobName,serverIp,"on");
                return true;
            }
            logger.info(jobName+"已被其他服务器执行");
            return false;
        }

二、数据库表

CREATE TABLE `job_manager` (
      `job_name` varchar(50) NOT NULL PRIMARY KEY COMMENT '名称',
      `job_desc` varchar(50)  COMMENT 'job描述',
      `server_ip` varchar(50) NOT NULL COMMENT '服务器ip',
      `on_off` varchar(10) DEFAULT 'off' COMMENT '开关(on:正在执行,off:执行完毕)',
      `update_date` datetime NOT NULL COMMENT '更新时间'
    ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='job管理' ROW_FORMAT=DYNAMIC;
    
    
    INSERT INTO `job_manager`
    VALUES
    ('xxx','更新xxx的job','0.0.0.0','off',now());

三、查询或改状态的sql

如下sql中：on\_off = 'off' AND update\_date < curdate(),是可执行job的标志

<select id="getJobOff" parameterType="string" resultType="int">
            SELECT count(1) FROM job_manager
            WHERE job_name = #{jobName} AND on_off = 'off' AND update_date < curdate()
        </select>
    
        <update id="updateJobStatus" parameterType="map">
            UPDATE job_manager
            SET on_off=#{status},server_ip=#{serverIp},update_date=now()
            WHERE job_name = #{jobName}
        </update>