基于redis的分布式锁

女爷i 2022-05-16 14:04 181阅读 0赞

## 锁实现代码 ##

public class RedisLock { 
    
        private final Logger log = LoggerFactory.getLogger(RedisLock.class);
        private static final Long RELEASE_SUCCESS = 1L;
    
        private String lockKey;
        private RedisConnectionFactory connectionFactory;
    
        public RedisLock(RedisConnectionFactory connectionFactory, String lockKey) {
            this.connectionFactory = connectionFactory;
            this.lockKey = lockKey;
        }
        /** * 加锁 * 取到锁加锁,并返回值用于解锁;取不到锁则立即返回-1 * @param milliTimeout 最长锁定时间,超时后自动删除锁,避免死锁 * @return */
        public synchronized long lock(long milliTimeout) {
            log.debug("开始执行加锁 ==> {}",lockKey);
            try (Jedis jedis = getJedis()) {
                /** * 生成随机数,用于解锁 * 保证解锁的线程和加锁的线程为同一个线程 */
                long lockValue = new Random(System.currentTimeMillis()).nextLong();
    
                // 保存成功返回"OK",否则返回null
                String result = jedis.set(lockKey, String.valueOf(lockValue), "NX", "PX", milliTimeout);
                if("OK".equals(result)) {
                    return lockValue;
                }
            } catch (Exception e) {
                throw new RuntimeException(e);
            }
            return -1;
        }
        /** * 解锁 * @param lockValue */
        public synchronized boolean unlock(Long lockValue) {
            boolean unlockSuccess = false;
            log.debug("执行解锁 ==> {}",lockKey);
            try (Jedis jedis = getJedis()) {
                String script = "if redis.call('get', KEYS[1]) == ARGV[1] then return redis.call('del', KEYS[1]) else return 0 end";
                Object result = jedis.eval(script, 1, lockKey.toString(), lockValue.toString());
                if (RELEASE_SUCCESS.equals(result)) {
                    log.debug("解锁成功 ==> {}",lockKey);
                    unlockSuccess = true;
                }
            } catch (Exception e) {
                log.error(e.getMessage(),e);
                throw new RuntimeException(e);
            }
            return unlockSuccess;
        }
    
        /** * springboot中通过反射从RedisConnectionFactory中获取jedis, * 因为redisTemplate封装set(key, value, "NX", "PX", milliTimeout)接口时没有返回值 */
        private Jedis getJedis() {
            Field jedisField = ReflectionUtils.findField(JedisConnection.class, "jedis");
            ReflectionUtils.makeAccessible(jedisField);
            Jedis jedis = (Jedis) ReflectionUtils.getField(jedisField, connectionFactory.getConnection());
            return jedis;
        }
    
    }

## 使用 ##

/* * springboot自动创建 */
        @Autowired
        private RedisConnectionFactory connectionFactory;
    
        public void testLock() {
    
            // redis分布式锁
            String key = "testLock-redis-lock";
            RedisLock lock = new RedisLock(connectionFactory, key);
    
            // 取不到锁立即返回-1
            long value = lock.lock(10000);
            if(value != -1) {
                log.debug("竞争锁成功 ==> {}",key);
                try {
                    // TODO
                } catch (Exception e) {
                    log.error(e.getMessage(), e);
                } finally {
                    lock.unlock(value);
                }
            } else {
                log.debug("竞争锁失败 ==> {}",key);
            }
        }