Redis Set 集合操作

Set 是无序不重复集合，支持交集、并集、差集运算。适合标签、共同好友、抽奖等。

获取操作接口

SetOperations<String, Object> ops = redisTemplate.opsForSet();

SADD — 添加元素

// SADD key member... — 返回成功添加的数量
Long add(K key, V... values);

ops.add("user:1001:tags", "java", "spring", "redis");   // 3
ops.add("user:1001:tags", "java", "docker");            // 1（java 重复跳过）

SREM — 删除元素

// SREM key member... — 返回成功删除的数量
Long remove(K key, Object... values);

ops.remove("user:1001:tags", "docker");              // 1
ops.remove("user:1001:tags", "python", "docker");    // 0（都不存在）

查询操作

// SMEMBERS — 获取所有成员
Set<V> members(K key);

// SISMEMBER — 判断是否为成员
Boolean isMember(K key, Object o);

// SCARD — 获取成员数量
Long size(K key);

随机操作

// SRANDMEMBER — 随机获取（不移除）
V randomMember(K key);                          // 1 个
List<V> randomMembers(K key, long count);        // count 个（可能重复）
Set<V> distinctRandomMembers(K key, long count); // count 个（去重）

// SPOP — 随机弹出（移除）
V pop(K key);                    // 弹出 1 个
List<V> pop(K key, long count);  // 弹出 count 个

// 抽奖示例
String winner = (String) ops.pop("lottery:participants");
List<Object> winners = ops.pop("lottery:participants", 3);

SMOVE — 移动元素

// SMOVE source dest member
Boolean move(K key, V value, K destKey);

// 用户从"待审核"移到"已通过"
ops.move("set:pending", "user1001", "set:approved");

集合运算

差集 SDIFF

// key1 有但 key2 没有的元素
Set<V> difference(K key, K otherKey);
Set<V> difference(K key, Collection<K> otherKeys);

// 差集存入目标 key
Long differenceAndStore(K key, K otherKey, K destKey);
Long differenceAndStore(K key, Collection<K> otherKeys, K destKey);

// 示例：查未读消息
ops.add("msg:all", "m1", "m2", "m3", "m4", "m5");
ops.add("msg:read", "m1", "m3", "m5");
Set<Object> unread = ops.difference("msg:all", "msg:read");  // [m2, m4]

交集 SINTER

Set<V> intersect(K key, K otherKey);
Set<V> intersect(K key, Collection<K> otherKeys);
Long intersectAndStore(K key, K otherKey, K destKey);
Long intersectAndStore(K key, Collection<K> otherKeys, K destKey);

// 示例：计算共同好友
ops.add("friend:user1", "user2", "user3", "user4");
ops.add("friend:user2", "user1", "user3", "user5");
Set<Object> common = ops.intersect("friend:user1", "friend:user2");  // [user3]

并集 SUNION

Set<V> union(K key, K otherKey);
Set<V> union(K key, Collection<K> otherKeys);
Long unionAndStore(K key, K otherKey, K destKey);
Long unionAndStore(K key, Collection<K> otherKeys, K destKey);

// 示例：合并多个标签
ops.add("tag:art1", "java", "spring");
ops.add("tag:art2", "redis", "spring");
Set<Object> allTags = ops.union("tag:art1", "tag:art2");  // [java, spring, redis]

SSCAN — 分批遍历

Cursor<V> scan(K key, ScanOptions options);

Cursor<Object> cursor = ops.scan("large:set",
    ScanOptions.scanOptions().count(100).build());
while (cursor.hasNext()) {
    process(cursor.next());
}

方法速查表

方法	Redis 命令	返回值
add(K, V...)	SADD	Long
remove(K, Object...)	SREM	Long
members(K)	SMEMBERS	Set<V>
isMember(K, Object)	SISMEMBER	Boolean
size(K)	SCARD	Long
pop(K)	SPOP	V
pop(K, long)	SPOP	List<V>
randomMember(K)	SRANDMEMBER	V
randomMembers(K, long)	SRANDMEMBER	List<V>
distinctRandomMembers(K, long)	SRANDMEMBER	Set<V>
move(K, V, K)	SMOVE	Boolean
difference(K, K)	SDIFF	Set<V>
difference(K, Collection)	SDIFF	Set<V>
intersect(K, K)	SINTER	Set<V>
intersect(K, Collection)	SINTER	Set<V>
union(K, K)	SUNION	Set<V>
union(K, Collection)	SUNION	Set<V>
*AndStore(...)	*STORE	Long
scan(K, ScanOptions)	SSCAN	Cursor

实战：共同关注

@Service
public class FollowService {
    @Autowired
    private RedisTemplate<String, Object> redisTemplate;

    public void follow(Long userId, Long targetId) {
        ops.add("follow:" + userId, targetId.toString());
    }

    public void unfollow(Long userId, Long targetId) {
        ops.remove("follow:" + userId, targetId.toString());
    }

    public Set<Object> commonFollowing(Long u1, Long u2) {
        return ops.intersect("follow:" + u1, "follow:" + u2);
    }

    // 你可能认识的人（二度好友）
    public Set<Object> recommend(Long userId) {
        Set<Object> recs = new HashSet<>();
        for (Object f : ops.members("follow:" + userId)) {
            Set<Object> theirs = ops.difference(
                "follow:" + f, "follow:" + userId);
            recs.addAll(theirs);
        }
        recs.remove(userId.toString());
        return recs;
    }
}

实战：抽奖

@Service
public class LotteryService {
    @Autowired
    private RedisTemplate<String, Object> redisTemplate;

    public void enroll(String activityId, Long userId) {
        ops.add("lottery:" + activityId, userId.toString());
    }

    public List<Object> draw(String activityId, int count) {
        return ops.pop("lottery:" + activityId, count);
    }

    public Long count(String activityId) {
        return ops.size("lottery:" + activityId);
    }
}