P2 Sping Boot定时器实战 读取问题列表

有两方式实现：

1.获取所有问题，循环获取标签，然后将标签与问题数存储在一个集合里
2.获取所有标签，查询每个标签有多少个问题被它引用（时间复杂度大）
设置定时执行官网：https://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/scheduling/support/CronSequenceGenerator.html

"0 0 * * * *" = the top of every hour of every day.
"*/10 * * * * *" = every ten seconds.
"0 0 8-10 * * *" = 8, 9 and 10 o'clock of every day.
"0 0 6,19 * * *" = 6:00 AM and 7:00 PM every day.
"0 0/30 8-10 * * *" = 8:00, 8:30, 9:00, 9:30, 10:00 and 10:30 every day.
"0 0 9-17 * * MON-FRI" = on the hour nine-to-five weekdays
"0 0 0 25 12 ?" = every Christmas Day at midnight

使用第一种，使用定时任务将问题从数据库中取出来

package life.majiang.community.schedule;

import com.github.pagehelper.PageHelper;
import life.majiang.community.dto.QuestionDTO;
import life.majiang.community.mapper.QuestionMapper;
import life.majiang.community.model.Question;
import life.majiang.community.service.QuestionService;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Component;

import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;

/**
 * 热门标签定时器,此处是测试定时任务（每隔5秒打印日志）
 * 注意：需在main方法的那个类上添加@EnableScheduling注解
 */
@Component
@Slf4j
public class HotTagTasks {
    private List<QuestionDTO>  list = null;
    @Autowired
    private QuestionService questionService;

    private static final SimpleDateFormat dateFormat = new SimpleDateFormat("HH:mm:ss");
    @Scheduled(fixedRate = 1000)
    //@Scheduled(cron = "0 0 1 * * *")//每天凌晨1点执行

    public void hotTagSchedule() {

        int offset = 0;
        int limit = 5;
        String search=null;
        log.info("hotTagSchedule start {}", dateFormat.format(new Date()));
        while (offset ==0 || list.size()==limit){
            list = questionService.list(search, offset, limit);
            for (QuestionDTO questionDTO : list) {
                log.info("list question :{}",questionDTO.getId());
            }
            offset +=limit;
        }
        log.info("hotTagSchedule stop {}", dateFormat.format(new Date()));
    }
}

测试结果：