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<dependency>

  <groupId>redis.clients</groupId>

  <artifactId>jedis</artifactId>

  <version>2.9.0</version>

</dependency>

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public class RedisTool {

  private static final String LOCK_SUCCESS = "OK";

  private static final String SET_IF_NOT_EXIST = "NX";

  private static final String SET_WITH_EXPIRE_TIME = "PX";

  /**

   * 尝试获取分布式锁

   * @param jedis Redis客户端

   * @param lockKey 锁

   * @param requestId 请求标识

   * @param expireTime 超期时间

   * @return 是否获取成功

   */

  public static boolean tryGetDistributedLock(Jedis jedis, String lockKey, String requestId, int expireTime) {

    String result = jedis.set(lockKey, requestId, SET_IF_NOT_EXIST, SET_WITH_EXPIRE_TIME, expireTime);

    if (LOCK_SUCCESS.equals(result)) {

      return true;

    }

    return false;

  }

}

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public static void wrongGetLock1(Jedis jedis, String lockKey, String requestId, int expireTime) {

  Long result = jedis.setnx(lockKey, requestId);

  if (result == 1) {

    // 若在这里程序突然崩溃，则无法设置过期时间，将发生死锁

    jedis.expire(lockKey, expireTime);

  }

}

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public static boolean wrongGetLock2(Jedis jedis, String lockKey, int expireTime) {

  long expires = System.currentTimeMillis() + expireTime;

  String expiresStr = String.valueOf(expires);

  // 如果当前锁不存在，返回加锁成功

  if (jedis.setnx(lockKey, expiresStr) == 1) {

    return true;

  }

  // 如果锁存在，获取锁的过期时间

  String currentValueStr = jedis.get(lockKey);

  if (currentValueStr != null && Long.parseLong(currentValueStr) < System.currentTimeMillis()) {

    // 锁已过期，获取上一个锁的过期时间，并设置现在锁的过期时间

    String oldValueStr = jedis.getSet(lockKey, expiresStr);

    if (oldValueStr != null && oldValueStr.equals(currentValueStr)) {

      // 考虑多线程并发的情况，只有一个线程的设置值和当前值相同，它才有权利加锁

      return true;

    }

  }   

  // 其他情况，一律返回加锁失败

  return false;

}

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public class RedisTool {

  private static final Long RELEASE_SUCCESS = 1L;

  /**

   * 释放分布式锁

   * @param jedis Redis客户端

   * @param lockKey 锁

   * @param requestId 请求标识

   * @return 是否释放成功

   */

  public static boolean releaseDistributedLock(Jedis jedis, String lockKey, String requestId) {

    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, Collections.singletonList(lockKey), Collections.singletonList(requestId));

    if (RELEASE_SUCCESS.equals(result)) {

      return true;

    }

    return false;

  }

}

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public static void wrongReleaseLock1(Jedis jedis, String lockKey) {

  jedis.del(lockKey);

}

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public static void wrongReleaseLock2(Jedis jedis, String lockKey, String requestId) {  

  // 判断加锁与解锁是不是同一个客户端

  if (requestId.equals(jedis.get(lockKey))) {

    // 若在此时，这把锁突然不是这个客户端的，则会误解锁

    jedis.del(lockKey);

  }

}