需求：

  • 开发关注、取消关注功能
  • 统计用户的关注数、粉丝数

关键：

  • 若A关注了B，则A是B的follower（粉丝），B是A的followee（目标）
  • 关注的目标可以是用户、帖子、题目等，在实现的时候将这些目标抽象为实体

1、设置新的RedisKey,用zset存储

/**
     * 某个用户关注的实体(用户、帖子等)
     * 格式：followee:userId:entityType -> zset(entityId,now)
     */
    public static String getFolloweeKey(int userId, int entityType) {
        return PREFIX_FOLLOWEE + SPLIT + userId + SPLIT + entityType;
    }

    /**
     * 某个实体拥有的粉丝
     * follower:entityType:entityId ->zset(userId,now)
     */
    public static String getFollowerKey(int entityType,int entityId){
        return PREFIX_FOLLOWER + SPLIT + entityType + SPLIT + entityId;
    }

2、在service新增方法，关注、取消关注、关注数量、粉丝数量、是否关注

@Service
public class FollowService implements CommunityConstant {

    @Autowired
    private RedisTemplate redisTemplate;

    @Autowired
    private UserService userService;

    //关注
    public void follow(int userId, int entityType, int entityId) {
        redisTemplate.execute(new SessionCallback() {
            @Nullable
            @Override
            public Object execute(RedisOperations redisOperations) throws DataAccessException {
                String followeeKey = RedisKeyUtil.getFolloweeKey(userId, entityType);
                String followerKey = RedisKeyUtil.getFollowerKey(entityType, entityId);

                redisOperations.multi();

                redisOperations.opsForZSet().add(followeeKey, entityId, System.currentTimeMillis());
                redisOperations.opsForZSet().add(followerKey, userId, System.currentTimeMillis());

                return redisOperations.exec();
            }
        });
    }
    //取消关注
    public void unfollow(int userId, int entityType, int entityId) {
        redisTemplate.execute(new SessionCallback() {
            @Nullable
            @Override
            public Object execute(RedisOperations redisOperations) throws DataAccessException {
                String followeeKey = RedisKeyUtil.getFolloweeKey(userId, entityType);
                String followerKey = RedisKeyUtil.getFollowerKey(entityType, entityId);

                redisOperations.multi();

                redisOperations.opsForZSet().remove(followeeKey, entityId);
                redisOperations.opsForZSet().remove(followerKey, userId);

                return redisOperations.exec();
            }
        });
    }

    //查询关注的实体的数量
    public long findFolloweeCount(int userId, int entityType) {
        String followeeKey = RedisKeyUtil.getFolloweeKey(userId, entityType);
        return redisTemplate.opsForZSet().zCard(followeeKey);
    }

    //查询实体粉丝数量
    public long findFollowerCount(int entityType, int entityId) {
        String followerKey = RedisKeyUtil.getFollowerKey(entityType, entityId);
        return redisTemplate.opsForZSet().zCard(followerKey);
    }

    //查询当前用户是否已关注该实体
    public boolean hasFollowed(int userId, int entityType, int entityId) {
        String followeeKey = RedisKeyUtil.getFolloweeKey(userId, entityType);
        return redisTemplate.opsForZSet().score(followeeKey, entityId) != null;
    }
}

3、在新增followcontroller，实现follow和unfollow方法，并在usercontroller中把粉丝数量、关注数量、是否关注的信息传过去

followController

@Controller
public class FollowController implements CommunityConstant {

    @Autowired
    private FollowService followService;

    @Autowired
    private HostHolder hostHolder;

    @Autowired
    private UserService userService;

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

        followService.follow(user.getId(), entityType, entityId);

        return CommunityUtil.getJSONString(0, "已关注！");
    }

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

        followService.unfollow(user.getId(), entityType, entityId);

        return CommunityUtil.getJSONString(0, "已取消关注！");
    }
}

userController

//个人主页
    @RequestMapping(value = "/profile/{userId}", method = RequestMethod.GET)
    public String getProfilePage(@PathVariable("userId") int userId, Model model) {
        User user = userService.findUserById(userId);
        if (user == null) {
            throw new RuntimeException("该用户不存在！");
        }
        //用户
        model.addAttribute("user", user);
        //点赞数量
        int likeCount = likeService.findUserLikeCount(userId);
        model.addAttribute("likeCount", likeCount);
        //关注数量
        long followeeCount = followService.findFolloweeCount(userId, ENTITY_TYPE_USER);
        model.addAttribute("followeeCount", followeeCount);
        //粉丝数量
        long followerCount = followService.findFollowerCount(ENTITY_TYPE_USER, userId);
        model.addAttribute("followerCount", followerCount);
        //是否已关注
        boolean hasFollowed = followService.hasFollowed(hostHolder.getUser().getId(), ENTITY_TYPE_USER, userId);
        model.addAttribute("hasFollowed", hasFollowed);

        return "/site/profile";
    }

4、前台html和js

把传递过来的值显示在页面上
这里要注意：
当用户是本人的时候，不显示关注按钮
当用户点击关注按钮之后，按钮更换样式，变成灰色

//html
<div class="media mt-5">
                    <img th:src="${user.headerUrl}" class="align-self-start mr-4 rounded-circle" alt="用户头像" style="width:50px;">
                    <div class="media-body">
                        <h5 class="mt-0 text-warning">
                            <span th:text="${user.username}">nowcoder</span>
                            <input type="hidden" id="entityId" th:value="${user.id}">
                            <button type="button" th:class="|btn ${hasFollowed?'btn-secondary':'btn-info'} btn-sm float-right mr-5 follow-btn|" th:text="${hasFollowed?'已关注':'关注TA'}" th:if="${loginUser!=null&&loginUser.id!=user.id}">关注TA</button>
                        </h5>
                        <div class="text-muted mt-3">
                            <span>注册于 <i class="text-muted" th:text="${#dates.format(user.createTime,'yyyy-MM-dd HH:mm:ss')}">2015-06-12 15:20:12</i></span>
                        </div>
                        <div class="text-muted mt-3 mb-5">
                            <span>关注了 <a class="text-primary" th:href="@{|/followees/${user.id}|}" th:text="${followeeCount}">5</a> 人</span>
                            <span class="ml-4">关注者 <a class="text-primary" th:href="@{|/followers/${user.id}|}"  th:text="${followerCount}">123</a> 人</span>
                            <span class="ml-4">获得了 <i class="text-danger" th:text="${likeCount}">87</i> 个赞</span>
                        </div>
                    </div>
                </div>
//js
$(function(){
    $(".follow-btn").click(follow);
});

function follow() {
    var btn = this;
    if($(btn).hasClass("btn-info")) {
        // 关注TA
        $.post(
            CONTEXT_PATH + "/follow",
            {"entityType":3,"entityId":$(btn).prev().val()},
            function (data) {
                data = $.parseJSON(data);
                if(data.code == 0){
                    window.location.reload();
                }else{
                    alert(data.msg);
                }
            }
        )

        // $(btn).text("已关注").removeClass("btn-info").addClass("btn-secondary");
    } else {
        // 取消关注
        // $(btn).text("关注TA").removeClass("btn-secondary").addClass("btn-info");
        $.post(
            CONTEXT_PATH + "/unfollow",
            {"entityType":3,"entityId":$(btn).prev().val()},
            function (data) {
                data = $.parseJSON(data);
                if(data.code == 0){
                    window.location.reload();
                }else{
                    alert(data.msg);
                }
            }
        )
    }
}