宁海有做网站的吗会计培训班的费用是多少

使用redis的setnx命令放入数据并用此数据当锁完成业务（但是如果用户操作途中出现异常导致超出指定时间会出现问题）

@Service
public class StockService {@Autowiredprivate StockDao stockDao;	//mapper注入@Autowiredprivate StringRedisTemplate redisTemplate;	//使用redis方法//public String decrement(Integer productid) {ValueOperations<String, String> opsForValue = redisTemplate.opsForValue();//1.获取共享锁资源（通过进行redis放入数据的方式，如果放入成功说明redis没有该数据）Boolean flag = opsForValue.setIfAbsent("product::" + productid, "1111", 30, TimeUnit.SECONDS);//表示获取锁成功if(flag) {try {//根据id查询商品的库存int num = stockDao.findById(productid);if (num > 0) {//修改库存stockDao.update(productid);System.out.println("商品编号为:" + productid + "的商品库存剩余:" + (num - 1) + "个");return "商品编号为:" + productid + "的商品库存剩余:" + (num - 1) + "个";} else {System.out.println("商品编号为:" + productid + "的商品库存不足。");return "商品编号为:" + productid + "的商品库存不足。";}}finally {//释放锁资源（删除放入的该数据，然后准备开始下一次抢锁）redisTemplate.delete("product::"+productid);}}else{//休眠100毫秒 在继续抢锁try {Thread.sleep(100);} catch (InterruptedException e) {throw new RuntimeException(e);}return decrement(productid);}}
}

看门狗（改善版，解决了超时的bug）

引入依赖

<dependency><groupId>org.redisson</groupId><artifactId>redisson</artifactId><version>3.24.3</version>
</dependency>

编写配置类

@Configuration
public class RedissonConfig {@Beanpublic RedissonClient redisson(){Config config = new Config();//连接redis集群config.useClusterServers()use "rediss://" for SSL connection.addNodeAddress("redis://127.0.0.1:7181","","","");//连接单机config.useSingleServer().setAddress("redis://192.168.111.188:6379");RedissonClient redisson = Redisson.create(config);return redisson;}
}

业务代码

@Service
public class StockService {@Autowiredprivate StockDao stockDao;	//注入mapper@Autowiredprivate RedissonClient redisson;	//注入看门狗//public String decrement(Integer productid) {RLock lock = redisson.getLock("product::" + productid);	//获取锁资源lock.lock();	//上锁try {//根据id查询商品的库存: 提前预热到redis缓存中int num = stockDao.findById(productid);if (num > 0) {//修改库存---incr---定时器[redis  数据库同步]stockDao.update(productid);System.out.println("商品编号为:" + productid + "的商品库存剩余:" + (num - 1) + "个");return "商品编号为:" + productid + "的商品库存剩余:" + (num - 1) + "个";} else {System.out.println("商品编号为:" + productid + "的商品库存不足。");return "商品编号为:" + productid + "的商品库存不足。";}}finally {lock.unlock();	//释放锁资源}}
}