Redis を使用して分散ロックを実装する方法

redis> EXISTS job                # job 不存在
(integer) 0

redis> SETNX job "programmer"    # job 设置成功
(integer) 1

redis> SETNX job "code-farmer"   # 尝试覆盖 job ，失败
(integer) 0

redis> GET job                   # 没有被覆盖
"programmer"

@Component
public class RedisDao {

	@Autowired
	private RedisTemplate redisTemplate;
	
	@Resource(name="redisTemplate")
	private ValueOperations<Object, Object> valOpsObj;
	
	/**
	 * 如果key不存在，就存储一个key-value，相当于SETNX命令
	 * @param key      键
	 * @param value    值，可以为空
	 * @return
	 */
	public boolean setIfObsent (String key, String value) {
		return valOpsObj.setIfAbsent(key, value);
	}
	
	/**
	 * 为key设置失效时间
	 * @param key       键
	 * @param timeout   时间大小
	 * @param unit      时间单位
	 */
	public boolean expire (String key, long timeout, TimeUnit unit) {
		return redisTemplate.expire(key, timeout, unit);
	}
	
	/**
	 * 删除key
	 * @param key 键
	 */
	public void delete (String key) {
		redisTemplate.delete(key);
	}
}

@RestController
@RequestMapping("test")
public class TestController {

	private static final Logger LOG = LoggerFactory.getLogger(TestController.class);  //日志对象
	@Autowired
	private RedisDao redisDao;
	//定义的分布式锁key
	private static final String LOCK_KEY = "MyTestLock";
	
	@RequestMapping(value={"testRedisLock"}, method=RequestMethod.GET)
	public void testRedisLock () {
		ExecutorService executorService = Executors.newFixedThreadPool(5);
		for (int i = 0; i < 5; i++) {
			executorService.submit(new Runnable() {
				@Override
				public void run() {
				    //获取分布式锁
					boolean flag = redisDao.setIfObsent(LOCK_KEY, "lock");
					if (flag) {
						LOG.info(Thread.currentThread().getName() + "：获取Redis分布式锁成功");
						//获取锁成功后设置失效时间
						redisDao.expire(LOCK_KEY, 2, TimeUnit.SECONDS);
						try {
							LOG.info(Thread.currentThread().getName() + "：处理业务开始");
							Thread.sleep(1000); //睡眠1000ms模拟处理业务
							LOG.info(Thread.currentThread().getName() + "：处理业务结束");
							//处理业务完成后删除锁
							redisDao.delete(LOCK_KEY);
						} catch (InterruptedException e) {
							LOG.error("处理业务异常：", e);
						}
					} else {
						LOG.info(Thread.currentThread().getName() + "：获取Redis分布式锁失败");
					}
				}
			});
		}
	}
}

/**
* Redis访问工具类
*/
@Component
public class RedisDao {

	private static Logger logger = LoggerFactory.getLogger(RedisDao.class);
	
	@Autowired
	private StringRedisTemplate stringRedisTemplate;
	
	/**
	 * 设置分布式锁    
	 * @param key     键
	 * @param value   值
	 * @param timeout 失效时间
	 * @return
	 */
	public boolean setDistributeLock (String key, String value, long timeout) {
		RedisConnection connection = null;
		boolean flag = false;
		try {
			//获取一个连接
			connection = stringRedisTemplate.getConnectionFactory().getConnection();
			//设置分布式锁的同时为锁设置失效时间
			connection.set(key.getBytes(), value.getBytes(), Expiration.seconds(timeout), RedisStringCommands.SetOption.SET_IF_ABSENT);
			flag = true;
		} catch (Exception e) {
			logger.error("set automic lock error:", e);
		} finally {
			//使用后关闭连接
			connection.close();
		}
		return flag;
	}
	
	/**
	 * 查询key的失效时间
	 * @param key       键
	 * @param timeUnit  时间单位
	 * @return
	 */
	public long ttl (String key, TimeUnit timeUnit) {
		return stringRedisTemplate.getExpire(key, timeUnit);
	}
}

/**
* 单元测试类
*/
@RunWith(SpringRunner.class)
@SpringBootTest
public class Demo1ApplicationTests {

	private static final Logger LOG = LoggerFactory.getLogger(Demo1ApplicationTests.class);
		
	@Autowired
	private RedisDao redisDao;
	
	@Test
	public void testDistributeLock () {
		String key = "MyDistributeLock";
		//设置分布式锁，失效时间20s
		boolean result = redisDao.setDistributeLock(key, "1", 20);
		if (result) {
			LOG.info("设置分布式锁成功");
			long ttl = redisDao.ttl(key, TimeUnit.SECONDS);
			LOG.info("{}距离失效还有{}s", key, ttl);
		}
	}
}

2019-05-15 13:07:10.827 - 设置分布式锁成功
2019-05-15 13:07:10.838 - MyDistributeLock距离失效还有19s