raex_back/src/main/java/com/izouma/nineth/service/UserHoldCountService.java

package com.izouma.nineth.service;

import com.izouma.nineth.config.Constants;
import com.izouma.nineth.dto.PageQuery;
import com.izouma.nineth.dto.PageWrapper;
import com.izouma.nineth.dto.UserHoldDTO;
import com.izouma.nineth.exception.BusinessException;
import lombok.AllArgsConstructor;
import org.apache.commons.collections.CollectionUtils;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.stereotype.Service;

import java.util.ArrayList;
import java.util.List;

@Service
@AllArgsConstructor
public class UserHoldCountService {
    private RedisTemplate<String, Object> redisTemplate;

    public PageWrapper<UserHoldDTO> all(PageQuery pageQuery) {
        if (Boolean.FALSE.equals(redisTemplate.hasKey(Constants.USER_HOLD_CACHE_KEY))) {
            throw new BusinessException("key失效，请刷新！如果已经刷新，请等待！");
        }
        // 当前页
        int page = pageQuery.getPage();
        // pageSize 每页查询多少条数据
        int size = pageQuery.getSize();
        // limit 开始偏移量
        int start = page * size;
        List<UserHoldDTO> userHoldDTOS = (List<UserHoldDTO>) redisTemplate.opsForValue().get(Constants.USER_HOLD_CACHE_KEY);
        int totalElements;
        if (CollectionUtils.isEmpty(userHoldDTOS)) {
            totalElements = 0;
            return new PageWrapper<>(new ArrayList<>(), page,
                    size, totalElements);
        }
        totalElements = userHoldDTOS.size();
        List<UserHoldDTO> newUserHoldList;
        if (userHoldDTOS.size() < start + size) {
            newUserHoldList = userHoldDTOS.subList(start, userHoldDTOS.size());
        } else {
            newUserHoldList = userHoldDTOS.subList(start, start + size);
        }
        return new PageWrapper<>(newUserHoldList, page,
                size, totalElements);
    }

}