Jedis实现分布式锁

添加依赖

      <dependency><groupId>redis.clients</groupId><artifactId>jedis</artifactId><version>3.3.0</version></dependency>

编码实现

public class RedisLockTest {private static int count = 0;private static String lockKey = "lock";private static void call(Jedis jedis) {// 生成标识，由于超时原因可能导致释放其他线程的锁，释放锁时保证是释放自己的锁String requestId = UUID.randomUUID().toString();// 加锁boolean locked = tryLock(jedis, lockKey, requestId, 60);try {if (locked) {for (int i = 0; i < 1000; i++) {count++;}}} catch (Exception e) {e.printStackTrace();} finally {unlock(jedis, lockKey, requestId);}}/*** 尝试获取分布式锁** @param jedis      Redis客户端* @param lockKey    锁* @param requestId  锁的值* @param expireTime 超期时间* @return 是否获取成功*/public static boolean tryLock(Jedis jedis, String lockKey, String requestId, int expireTime) {// 自旋锁while (true) {// set key value ex seconds nx(只有键不存在的时候才会设置key)String result = jedis.set(lockKey, requestId, SetParams.setParams().ex(expireTime).nx());if ("OK".equals(result)) {return true;}}}/*** 释放分布式锁** @param jedis   Redis客户端* @param lockKey 锁* @return 是否释放成功*/public static boolean unlock(Jedis jedis, String lockKey, String requestId) {if (!requestId.equals(jedis.get(lockKey))) {return false;}Long result = jedis.del(lockKey);return 1L == result;}public static void main(String[] args) throws Exception {RedisLockTest redisLockTest = new RedisLockTest();JedisPoolConfig jedisPoolConfig = new JedisPoolConfig();jedisPoolConfig.setMinIdle(1);jedisPoolConfig.setMaxTotal(5);JedisPool jedisPool = new JedisPool(jedisPoolConfig, "127.0.0.1", 6379, 1000, null);Thread t1 = new Thread(() -> RedisLockTest.call(jedisPool.getResource()));Thread t2 = new Thread(() -> RedisLockTest.call(jedisPool.getResource()));t1.start();t2.start();t1.join();t2.join();System.out.println(redisLockTest.count);}
}

RedisTemplate实现分布式锁

加锁: 调用set命令设置值，能够设置成功则表示加锁成功  set lock_key lock_value NX PX 5000释放锁: 调用del命令来删除设置的键值  del lock_key

注意事项

当某个线程获取锁后程序挂掉，此时还没来得及释放锁，这样后面所有的线程都无法获取锁，所以在加锁时设置一个过期时间防止死锁。

加锁和解锁必须是同一个客户端，所以在加锁时可以设置当前线程id，在释放锁时判断是否为当前线程加的锁，如果是再释放锁。

编码实现

	@Autowiredprivate StringRedisTemplate redisTemplate;@GetMapping("/test")public String test() {try {// 获取当前线程idString threadId = Thread.currentThread().getId() + "";// 开始加锁Boolean locked = redisTemplate.opsForValue().setIfAbsent("lock", threadId, 5000, TimeUnit.MILLISECONDS);if (locked) {//加锁成功int stock = Integer.parseInt(redisTemplate.opsForValue().get("stock"));if (stock > 0) {stock--;redisTemplate.opsForValue().set("stock", stock + "");log.info("库存扣减成功，剩余库存：{}", stock);} else {log.info("库存不足，剩余库存：{}", stock);}String lockValue = redisTemplate.opsForValue().get("lock");if (threadId.equals(lockValue)) {//释放锁redisTemplate.delete("lock");}} else {log.info("获取锁失败...");}} catch (Exception ex) {log.info("出现异常....");}return "success";}

Redisson实现分布式锁

Redisson内置提供了基于Redis的分布式锁实现，该方式是推荐的分布式锁使用方式。

https://redisson.org/

添加依赖

<dependency><groupId>org.redisson</groupId><artifactId>redisson</artifactId><version>3.16.6</version>
</dependency>  

配置Redisson

@Configuration
public class RedissonConfig {@Value("${spring.redis.host}")private String host;@Value("${spring.redis.port}")private String port;@Value("${spring.redis.password}")private String password;@Beanpublic RedissonClient redissonClient() {Config config = new Config();config.useSingleServer().setAddress("redis://" + host + ":" + port);config.useSingleServer().setPassword(password);return Redisson.create(config);}
}

编码实现

	@Autowiredprivate RedissonClient redissonClient;@GetMapping("/test")public String test() {//获得分布式锁对象RLock lock = redissonClient.getLock("lock");try {//尝试加锁，如果加锁成功则后续程序继续执行，如果加锁不成功则阻塞等待lock.lock(5000, TimeUnit.MILLISECONDS);int stock = Integer.parseInt(redisTemplate.opsForValue().get("stock"));if (stock > 0) {stock--;redisTemplate.opsForValue().set("stock", stock + "");log.info("库存扣减成功，剩余库存：{}", stock);} else {log.info("库存不足，剩余库存：{}", stock);}} catch (Exception exception) {log.info("出现异常....");} finally {//解锁lock.unlock();}return "success";}
}

ZooKeeper实现分布式锁

Zookeeper中节点分为4种类型：

持久节点 （PERSISTENT）

默认的节点类型。创建节点的客户端与zookeeper断开连接后，该节点依旧存在

持久顺序节点（PERSISTENT_SEQUENTIAL）

顺序节点就是在创建节点时，Zookeeper根据创建的时间顺序给该节点名称进行编号

临时节点（EPHEMERAL）

和持久节点相反，当创建节点的客户端与zookeeper断开连接后，临时节点会被删除

临时顺序节点（EPHEMERAL_SEQUENTIAL）

临时顺序节点结合和临时节点和顺序节点的特点：在创建节点时，Zookeeper根据创建的时间顺序给该节点名称进行编号；当创建节点的客户端与zookeeper断开连接后，临时节点会被删除

Zookeeper实现分布式锁的原理是基于Zookeeper的临时顺序节点

Apache Curator 是用于分布式协调服务Apache ZooKeeper的 Java/JVM 客户端库。它包括一个高级 API 框架和实用程序，使用 Apache ZooKeeper 变得更加容易和可靠。

Apache Curator官网: https://curator.apache.org/

添加依赖

	    <dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-data-redis</artifactId></dependency><dependency><groupId>org.apache.curator</groupId><artifactId>curator-framework</artifactId><version>4.2.0</version><exclusions><exclusion><groupId>org.apache.zookeeper</groupId><artifactId>zookeeper</artifactId></exclusion></exclusions></dependency><dependency><groupId>org.apache.curator</groupId><artifactId>curator-recipes</artifactId><version>4.2.0</version></dependency><dependency><groupId>org.apache.zookeeper</groupId><artifactId>zookeeper</artifactId><version>3.4.14</version></dependency>

配置Zookeeper

@Configuration
public class ZkConfig {@Beanpublic CuratorFramework curatorFramework(){RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000,3);CuratorFramework client = CuratorFrameworkFactory.builder().connectString("IP:2181").sessionTimeoutMs(5000).connectionTimeoutMs(5000).retryPolicy(retryPolicy).build();client.start();return client;}
}

编码实现

    @Autowiredprivate CuratorFramework curatorFramework;@GetMapping("/test")public String test() {InterProcessMutex mutex = new InterProcessMutex(curatorFramework, "/lock");try {boolean locked = mutex.acquire(0, TimeUnit.SECONDS);if (locked) {int stock = Integer.parseInt(redisTemplate.opsForValue().get("stock"));if (stock > 0) {stock--;redisTemplate.opsForValue().set("stock", stock + "");log.info("库存扣减成功，剩余库存：{}", stock);} else {log.info("库存不足，剩余库存：{}", stock);}//释放锁mutex.release();} else {log.info("获取锁失败...");}} catch (Exception exception) {log.info("出现异常....");}return "success";}