(十七)在线教育网站搭建-将讲师列表和课程列表存入redis缓存

redis

1. 使用redis的列表

127.0.0.1:6379> lpush key value #从左插入value到key列表
127.0.0.1:6379> rpush key value #从右插入value到key列表
127.0.0.1:6379> llen key        #得到key列表长度
127.0.0.1:6379> del key         #删除key列表
127.0.0.1:6379> lrange teacher 0 20 #得到key列表的[0,20]元素

2. redis中文乱码问题

启动客户端采用 redis-cli –raw

3. 添加列表进redis

3.1. redis-Maven依赖

<!-- redis -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-redis</artifactId>
</dependency>
<!-- json转string -->
<dependency>
    <groupId>com.fasterxml.jackson.jaxrs</groupId>
    <artifactId>jackson-jaxrs-json-provider</artifactId>
    <version>2.10.0</version>
</dependency>

3.2. service中的实现

从右插入列表，从左读出列表

开始时，redis中没有数据，从数据库中取数据放入redis中，并存入teacherTotal用于判断redis中数据是否存入

而后就从redis中取数据，但后台可能增加讲师记录，所以设置缓存时效为1天

3.2.1. 讲师

@Autowired
StringRedisTemplate redisTemplate;

//前端展示页面
@Override
public Map<String, Object> frontListPageTeacher(String current, String size) {

    Long currentPage = Long.parseLong(current);
    Long pageSize = Long.parseLong(size);

    Long total = 0L;

    List<EduTeacher> results = new ArrayList<>();

    //存入所有记录
    Map<String,Object> map = new HashMap<>();


    try{
        ObjectMapper objectMapper = new ObjectMapper();

        String key = redisTemplate.opsForValue().get("teacherTotal");

        if(!StringUtils.isEmpty(key)) {

            total = Long.parseLong(key);
            List<String> teachers = redisTemplate.opsForList().range("teacher",
                    pageSize * (currentPage - 1), pageSize * currentPage-1);

            for(String str:teachers){
                EduTeacher  teacher= objectMapper.readValue(str, EduTeacher.class);
                results.add(teacher);
            }

        }else{

            Page<EduTeacher> page = new Page<>(currentPage,pageSize);
            //结果 按sort降序，相同时按id升序
            QueryWrapper<EduTeacher> queryWrapper = new QueryWrapper<>();
            queryWrapper.orderByDesc("sort");
            queryWrapper.orderByAsc("id");

            Page<EduTeacher> eduTeacherPage = baseMapper.selectPage(page, queryWrapper);
          
            //得到页内容
            results = eduTeacherPage.getRecords();
            //得到所有记录数
            total = eduTeacherPage.getTotal();
            //存1天
            redisTemplate.opsForValue().set("teacherTotal",total+"",1,TimeUnit.DAYS);

            List<EduTeacher> teachers = baseMapper.selectList(queryWrapper);
            for(EduTeacher teacher: teachers){
                String obj =  objectMapper.writeValueAsString(teacher);

                redisTemplate.opsForList().rightPush("teacher",obj);

                //System.out.println(redisTemplate.opsForList().size("teacher"));
            }
            redisTemplate.expire("teacher",1, TimeUnit.DAYS);

        }
    } catch (JsonProcessingException e) {
        throw new EduException(20001,"json无法转字符串");
    }

    //存入所有记录
    map.put("total",total);
    map.put("items",results);

    return map;
}

3.2.2. 课程

//前台分页查询课程信息
@Override
public Map<String,Object> frontSelectPage(String current, String size) {

    Long currentPage = Long.parseLong(current);
    Long pageSize = Long.parseLong(size);

    Long total = 0L;

    List<EduCourse> results = new ArrayList<>();

    //存入所有记录
    Map<String,Object> map = new HashMap<>();


    try {
        ObjectMapper objectMapper = new ObjectMapper();

        String key = redisTemplate.opsForValue().get("courseTotal");

        if(!StringUtils.isEmpty(key)) {
            total = Long.parseLong(key);

            List<String> courses = redisTemplate.opsForList().range("course",
                    pageSize*(currentPage-1),pageSize*currentPage-1);

            for(String str:courses){
                EduCourse  teacher= objectMapper.readValue(str, EduCourse.class);
                results.add(teacher);
            }

        }else{

            Page<EduCourse> page = new Page<>(currentPage,pageSize);

            Page<EduCourse> eduCoursePage = baseMapper.selectPage(page,null);

            results = eduCoursePage.getRecords();

            total = eduCoursePage.getTotal();
            redisTemplate.opsForValue().set("courseTotal",total+"",1, TimeUnit.DAYS);

            List<EduCourse> courses = baseMapper.selectList(null);
            for(EduCourse course: courses){
                String obj =  objectMapper.writeValueAsString(course);

                redisTemplate.opsForList().rightPush("course",obj);

                //System.out.println(redisTemplate.opsForList().size("course"));
            }
            redisTemplate.expire("course",1, TimeUnit.DAYS);

        }
    } catch (Exception e) {
       throw  new EduException(20001,"稍后再试");
    }

    map.put("total",total);
    map.put("courses",results);

    return map;
}