今天面试官问Redis分布式锁实现代码简单步骤，其中有一点面试官坚持说set操作和超时设置必须是2行代码，我当时懵了一下，我只能说这违反了“原子”操作，以下是我的实现示例代码：
上锁：
@Override
public boolean lock(String lockKey, String requestId, Long expireTime) {
Assert.isTrue(StringUtils.isNotBlank(lockKey), "lockKey不能为空");
Assert.isTrue(StringUtils.isNotBlank(requestId), "请求标识不能为空");
Object result = stringRedisTemplate.execute(new RedisCallback<Boolean>() {
@Override
public Boolean doInRedis(RedisConnection connection) throws DataAccessException {
Expiration expiration = Expiration.milliseconds(null == expireTime ? 1000L * 60 : expireTime);
byte[] key = lockKey.getBytes(Charset.forName("UTF-8"));
byte[] value = requestId.getBytes(Charset.forName("UTF-8"));
return connection.set(key, value, expiration, SetOption.SET_IF_ABSENT);
}
});
return (null == result) ? false : result.equals(true);
}释放锁：
@Override
public boolean unlock(String lockKey, String requestId) {
Assert.isTrue(StringUtils.isNotBlank(lockKey), "lockKey不能为空");
Assert.isTrue(StringUtils.isNotBlank(requestId), "请求标识不能为空");
String lua = "if redis.call('get', KEYS[1]) == ARGV[1] then return redis.call('del', KEYS[1]) else return 0 end";
Object result = stringRedisTemplate.execute(new RedisCallback<Boolean>() {
@Override
public Boolean doInRedis(RedisConnection connection) throws DataAccessException {
byte[] script = lua.getBytes(Charset.forName("UTF-8"));
byte[] key = lockKey.getBytes(Charset.forName("UTF-8"));
byte[] value = requestId.getBytes(Charset.forName("UTF-8"));
Long result = connection.eval(script, ReturnType.INTEGER, 1, key, value);
return (null == result ? false : result.equals(1L));
}
});
return (null == result) ? false : result.equals(true);
/* 若redis是2.6.0以下版本，则不支持lua脚本，只能降级采用redisTemplate.delete解锁，但不能保证原子操作 */
}