Redis 场景

1.分布式锁实现

上锁：setnx key value

解锁：del key

超时机制：set key value nx ex time

基于此思路实现伪代码：

public class RedisLock{@Autowiredprivate static RedisTemplate rt;  private static final LOCK_WORD = "lock";private static final int TIME_OUT = 3;public void tryLock(String uuid ){//String uuid = UUID.get();boolean lock = rt.setnx(LOCK_WORD,uuid,TIME_OUT,TimeUnit.SECOND);if(lock){			//	没有考虑可重入锁设计try{do(业务逻辑)}finally{	//	需要保证原子操作String tempLock = rt.get(LOCK_WORD);if(uuid.equals(tempLock)){rt.del(LOCK_WORD);}}       }else {try{Thread.sleep(100);tryLock();	//	递归调用可能会爆栈，应该实现一个等待队列}catch(InterruptedException e){e.printStackTrace();}}}
}

实际实现代码：

@GetMapping("testLock")
public void testLock() {// 1 获取锁，setIfAbsent，同时设置3秒过期，以避免中间出现异常，导致锁一直无法释放Boolean lock = redisTemplate.opsForValue().setIfAbsent("lock", "111", 3, TimeUnit.SECONDS);// 2 获取锁成功，查询num的值if (lock) {Object value = redisTemplate.opsForValue().get("num");// 2.1 判断num为空，returnif (StringUtils.isEmpty(value)) {return;}// 2.2 有值就转成intint num = Integer.parseInt(value + "");// 2.3 把redis的num加1redisTemplate.opsForValue().set("num", ++num);// 2.4 释放锁，删除lockString lockUuid = (String) redisTemplate.opsForValue().get("lock");if ("111".equals(lockUuid)) {redisTemplate.delete("lock");}} else {// 3 获取锁失败，每隔0.1秒再获取try {Thread.sleep(100);testLock();} catch (InterruptedException e) {e.printStackTrace();}}
}

2.秒杀场景(解决超卖)

思路：

维护一个用户 id，商品 id，库存信息，秒杀成功名单
先确认库存正常，即秒杀开始
先查询 uid 是否在成功名单，避免重复秒杀
再查询库存是否充足，
利用事务完成：扣除库存、添加名单，秒杀成功

伪代码：

@Autowired
private RedisTemplate rt;public boolean doSecondKill(String uid,String productId){String successListKey = "User-"+productId;String invenKey = "Inventory-"+productId;if(rt.get(invenKey)==null){print("秒杀尚未开启");return false;}if(rt.sismember(successListKey,uid)){print("不可重复秒杀");return false;}if(Integer.parseInt(rt.get(invenKey))<=0){print("秒杀已结束");return false;}Transaction multi = rt.multi();multi.decr(invenKey);		//	扣除库存multi.sadd(successListKey,uid);	//	添加成功秒杀List<Object> result = multi.exec();if(result==null || result.size()==0){print("秒杀失败");return false;}print("秒杀成功");return true;
}

代码实现

public class SecKill {public static void main(String[] args) {Jedis jedis = new Jedis();}public static boolean doSecKill(String uid, String proid) throws IOException {//  1.uid和proid判断if (uid == null || proid == null) {return false;}// 2.连接jedis,使用连接池，避免超时JedisPool jedisPool = new JedisPool();Jedis jedis = jedisPool.getResource();//  3. 拼接keyString invenKey = "sk:" + proid + "qt";String userKey = "sk:" + proid + "qt";//  监视库存jedis.watch(invenKey);//  4. 判断是否开始String inven = jedis.get(invenKey);if (inven == null) {System.out.println("秒杀尚未开始");jedis.close();return false;}//  5.判断是否抢过if (jedis.sismember(userKey, uid)) {System.out.println("不可重复参与！");jedis.close();return false;}//  6.判断库存是否充足if (Integer.parseInt(jedis.get(invenKey)) <= 0) {System.out.println("秒杀已结束，失败");jedis.close();return false;}//  multi事务操作Transaction multi = jedis.multi();multi.decr(invenKey);multi.sadd(userKey, uid);List<Object> result = multi.exec();if (result == null || result.size() == 0) {System.out.println("秒杀失败");jedis.close();return false;}System.out.println("秒杀成功");jedis.close();return true;}
}