10、Redis实现点赞（Set）和获取总点赞数

实现点赞

不用写数据访问层，直接在Service层写即可。

1、创建RedisKeyUtil工具类生成key：

public class RedisKeyUtil {
    private static final String SPLIT = ":";
    private static final String PREFIX_ENTITY_LIKE = "like:entity";

    // 某个实体的赞
    // like:entity:entityType:entityId -> set(userId)
    public static String getEntityLikeKey(int entityType, int entityId) {
        return PREFIX_ENTITY_LIKE + SPLIT + entityType + SPLIT + entityId;
    }
}

2、LikeService

@Service
public class LikeService {

    @Autowired
    private RedisTemplate redisTemplate;

    // 点赞，查看该用户userId是否在集合里，没在集合里，加进去，即点赞；在集合里，取消点赞，remove掉
    public void like(int userId, int entityType, int entityId) {
        String entityLikeKey = RedisKeyUtil.getEntityLikeKey(entityType, entityId);
        boolean isMember = redisTemplate.opsForSet().isMember(entityLikeKey, userId);
        if (isMember) {
            redisTemplate.opsForSet().remove(entityLikeKey, userId);// 取消点赞
        } else {
            redisTemplate.opsForSet().add(entityLikeKey, userId);
        }
    }

    // 查询某实体点赞的数量，看集合里有多少个userId
    public long findEntityLikeCount(int entityType, int entityId) {
        String entityLikeKey = RedisKeyUtil.getEntityLikeKey(entityType, entityId);
        return redisTemplate.opsForSet().size(entityLikeKey);
    }

    // 查询某人对某实体的点赞状态，看某userId是否在集合里，返回1点赞了，返回0没点赞（点踩可以返回-1）
    public int findEntityLikeStatus(int userId, int entityType, int entityId) {
        String entityLikeKey = RedisKeyUtil.getEntityLikeKey(entityType, entityId);
        return redisTemplate.opsForSet().isMember(entityLikeKey, userId) ? 1 : 0;
    }
    
}

3、LikeController

@Controller
public class LikeController {

    @Autowired
    private LikeService likeService;

    @Autowired
    private HostHolder hostHolder;

    @RequestMapping(path = "/like", method = RequestMethod.POST)
    @ResponseBody
    public String like(int entityType, int entityId) {
        User user = hostHolder.getUser();

        // 点赞
        likeService.like(user.getId(), entityType, entityId);

        // 重新计算数量
        long likeCount = likeService.findEntityLikeCount(entityType, entityId);
        // 重新计算状态
        int likeStatus = likeService.findEntityLikeStatus(user.getId(), entityType, entityId);

        Map<String, Object> map = new HashMap<>();
        map.put("likeCount", likeCount);
        map.put("likeStatus", likeStatus);

        return CommunityUtil.getJSONString(0, null, map);
    }

}

4、异步请求，discuss.js

function like(btn, entityType, entityId) {
    $.post(
        CONTEXT_PATH + "/like",
        {"entityType":entityType,"entityId":entityId},
        function(data) {
            data = $.parseJSON(data);
            if(data.code == 0) {
                $(btn).children("i").text(data.likeCount);
                $(btn).children("b").text(data.likeStatus==1?'已赞':"赞");
            } else {
                alert(data.msg);
            }
        }
    );
}

获取总点赞数

1、改key拼接工具类RedisKeyUtil

	private static final String PREFIX_USER_LIKE = "like:user";
    // 某个用户的被点赞总数, value是Object->强转成Integer->intValue()转成int型
    // like:user:userId -> int
    public static String getUserLikeKey(int userId){
        return PREFIX_USER_LIKE + SPLIT + userId;
    }

2、LikeService，编程式事务

保证事务性，一次点赞两处增加，编程式事务

public void like(int userId, int entityType, int entityId, int entityUserId) {

        // 保证事务性，一次点赞两个增加，编程式事务
        redisTemplate.execute(new SessionCallback() {
            @Override
            public Object execute(RedisOperations operations) throws DataAccessException {
                String entityLikeKey = RedisKeyUtil.getEntityLikeKey(entityType, entityId);
                String userLikeKey = RedisKeyUtil.getUserLikeKey(entityUserId);

                // 查询要在事务之前，不能放在事务里面，否则事务提交之后才执行。
                boolean isMember = operations.opsForSet().isMember(entityLikeKey, userId);

                operations.multi();

                if (isMember) {
                    operations.opsForSet().remove(entityLikeKey, userId);// 取消点赞
                    operations.opsForValue().decrement(userLikeKey);// 减少实体的被点赞数
                }else{
                    operations.opsForSet().add(entityLikeKey, userId);// 点赞
                    operations.opsForValue().increment(userLikeKey);// 增加实体的被点赞数
                }

                return operations.exec();
            }
        });

    }

查询某个用户获得的赞的总数

// 查询某个用户获得的赞的总数
public int findUserLikeCount(int userId) {
    String userLikeKey = RedisKeyUtil.getUserLikeKey(userId);
    Integer count = (Integer) redisTemplate.opsForValue().get(userLikeKey);
    return count == null ? 0 : count.intValue();
}