Java单体项目和分布式项目中的锁

单体应用解决超卖问题

@Service
@Slf4j
public class OrderService {

    @Resource
    private OrderMapper orderMapper;
    @Resource
    private OrderItemMapper orderItemMapper;
    @Resource
    private ProductMapper productMapper;
    //购买商品id
    private int purchaseProductId = 100100;
    //购买商品数量
    private int purchaseProductNum = 1;
    @Autowired
    private PlatformTransactionManager platformTransactionManager;
    @Autowired
    private TransactionDefinition transactionDefinition;

    private Lock lock = new ReentrantLock();// 可重入锁

    public Integer createOrder() throws Exception{
        Product product = null;
        //上锁
        lock.lock();
        try {
            //手动开启事务
            TransactionStatus transaction1 = platformTransactionManager.getTransaction(transactionDefinition);
            product = productMapper.selectByPrimaryKey(purchaseProductId);
            if (product==null){
                //抛异常，回滚事务
                platformTransactionManager.rollback(transaction1);
                throw new Exception("购买商品："+purchaseProductId+"不存在");
            }
            //商品当前库存
            Integer currentCount = product.getCount();
            System.out.println(Thread.currentThread().getName()+"库存数："+currentCount);
            //校验库存
            if (purchaseProductNum > currentCount){
                //抛异常，回滚事务
                platformTransactionManager.rollback(transaction1);
                throw new Exception("商品"+purchaseProductId+"仅剩"+currentCount+"件，无法购买");
            }
            productMapper.updateProductCount(purchaseProductNum,"xxx",new Date(),product.getId());
            //正常执行，提交事务
            platformTransactionManager.commit(transaction1);
        }finally {
            // 释放锁
            lock.unlock();
        }

      // 其他创建订单业务逻辑
    }

}

我们再finally里面释放锁，方法还未结束，事务还未提交，高并发下，恰好在锁释放后，事务提交前，读到了未提交的脏数据，导致超卖！
解决上述问题，需要使用aop锁
1、定义注解：

@Target({ElementType.PARAMETER,ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface ServiceLock {

    String description() default "";

}

2、定义切面

@Component
@Scope
@Aspect
@Order(1) // 表示在事务之前执行
public class LockAspect {


    // 定义锁对象
    private static Lock lock = new ReentrantLock(true);

    @Pointcut("@annotation(com.sugo.seckill.aop.lock.ServiceLock)")
    public void lockAspect(){

    }

    // 增强方法
    @Around("lockAspect()")
    public Object around(ProceedingJoinPoint joinPoint){

        Object obj = null;
        // 加锁
        lock.lock();
        // 执行业务
        try {
            obj = joinPoint.proceed();
        } catch (Throwable throwable) {
            throwable.printStackTrace();
        } finally {
            // 释放锁
            lock.unlock();
        }

        return obj;

    }

}

3、使用注解

	@Transactional
	@ServiceLock
	@Override
	public HttpResult startKilledByLocked(Long killId, String userId) {
		try {

			// 从数据库查询商品数据
			TbSeckillGoods seckillGoods = seckillGoodsMapper.selectByPrimaryKey(killId);
			//判断
			if(seckillGoods == null){
				return HttpResult.error(HttpStatus.SEC_GOODS_NOT_EXSISTS,"商品不存在");
			}
			if(seckillGoods.getStatus() != 1){
				return HttpResult.error(HttpStatus.SEC_NOT_UP,"商品未审核");
			}
			if(seckillGoods.getStockCount() <= 0){
				return HttpResult.error(HttpStatus.SEC_GOODS_END,"商品已售罄");
			}
			if(seckillGoods.getStartTimeDate().getTime() > new Date().getTime()){
				return HttpResult.error(HttpStatus.SEC_ACTIVE_NOT_START,"活动未开始");
			}
			if(seckillGoods.getEndTimeDate().getTime() <= new Date().getTime()){
				return HttpResult.error(HttpStatus.SEC_ACTIVE_END,"活动结束");
			}

			//库存扣减
			seckillGoods.setStockCount(seckillGoods.getStockCount() - 1);
			//更新库存
			seckillGoodsMapper.updateByPrimaryKeySelective(seckillGoods);


			//下单
			TbSeckillOrder order = new TbSeckillOrder();
			order.setSeckillId(killId);
			order.setUserId(userId);
			order.setCreateTime(new Date());
			order.setStatus("0");
			order.setMoney(seckillGoods.getCostPrice());

			seckillOrderMapper.insertSelective(order);

			return HttpResult.ok("秒杀成功");
		} catch (Exception e) {
			e.printStackTrace();
		}
		return null;
	}

分布式锁

基于Redis实现分布式锁

依赖

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-redis</artifactId>
        </dependency>

定义RedisLock

@Slf4j
public class RedisLock implements AutoCloseable {

    private RedisTemplate redisTemplate;
    private String key;
    private String value;
    //单位：秒
    private int expireTime;

    public RedisLock(RedisTemplate redisTemplate,String key,int expireTime){
        this.redisTemplate = redisTemplate;
        this.key = key;
        this.expireTime=expireTime;
        this.value = UUID.randomUUID().toString();
    }

    /**
     * 获取分布式锁
     * @return
     */
    public boolean getLock(){
        RedisCallback<Boolean> redisCallback = connection -> {
            //设置NX
            RedisStringCommands.SetOption setOption = RedisStringCommands.SetOption.ifAbsent();
            //设置过期时间
            Expiration expiration = Expiration.seconds(expireTime);
            //序列化key
            byte[] redisKey = redisTemplate.getKeySerializer().serialize(key);
            //序列化value
            byte[] redisValue = redisTemplate.getValueSerializer().serialize(value);
            //执行setnx操作
            Boolean result = connection.set(redisKey, redisValue, expiration, setOption);
            return result;
        };

        //获取分布式锁
        Boolean lock = (Boolean)redisTemplate.execute(redisCallback);
        return lock;
    }

    /**
     * 释放分布式锁
     * @return
     */
    public boolean unLock() {
        String script = "if redis.call("get",KEYS[1]) == ARGV[1] thenn" +
                "    return redis.call("del",KEYS[1])n" +
                "elsen" +
                "    return 0n" +
                "end";
        RedisScript<Boolean> redisScript = RedisScript.of(script,Boolean.class);
        List<String> keys = Arrays.asList(key);

        Boolean result = (Boolean)redisTemplate.execute(redisScript, keys, value);
        log.info("释放锁的结果："+result);
        return result;
    }


    /**
     * 实现了AutoCloseable,实现自动释放锁,避免忘记释放锁
     * @throws Exception
     */
    @Override
    public void close() throws Exception {
        unLock();
    }
}

使用RedisLock

@RestController
@Slf4j
public class RedisLockController {
    @Autowired
    private RedisTemplate redisTemplate;

    @RequestMapping("redisLock")
    public String redisLock(){
        log.info("我进入了方法！");
        // redisKey是业务key,可以自定义
        try (RedisLock redisLock = new RedisLock(redisTemplate,"redisKey",30)){
            if (redisLock.getLock()) {
                log.info("我进入了锁！！");
                // 这里可以写具体并发业务
                Thread.sleep(15000);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        log.info("方法执行完成");
        return "方法执行完成";
    }
}

使用RedisLock就可以用@Scheduled实现分布式定时任务(启动类上要加@EnableScheduling)

@Service
@Slf4j
public class SchedulerService {
    @Autowired
    private RedisTemplate redisTemplate;

    @Scheduled(cron = "0/5 * * * * ?")
    public void sendSms(){
        // autoSms 是业务key, 可以自定义
        try(RedisLock redisLock = new RedisLock(redisTemplate,"autoSms",30)) {
            if (redisLock.getLock()){
                log.info("向138xxxxxxxx发送短信！");
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

上面同样有锁失效的问题，所以同样有Redis aop锁，具体实现如下：

@Target({ElementType.PARAMETER,ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface ServiceRedisLock {

    String description() default "";

}

@Component
@Scope
@Aspect
@Order(1) // 表示在事务之前执行
public class LockRedisAspect {

    @Pointcut("@annotation(com.sugo.seckill.aop.redis.ServiceRedisLock)")
    public void lockAspect(){

    }

    // 增强方法
    @Around("lockAspect()")
    public Object around(ProceedingJoinPoint joinPoint){
        Object obj = null;
        // 加锁
        boolean res = RedissLockUtil.tryLock(Constants.DISTRIBUTED_REDIS_LOCK_KEY,
                TimeUnit.SECONDS, 3,
                10);
        // 执行业务
        try {
            if(res){
                obj = joinPoint.proceed();
            }
        } catch (Throwable throwable) {
            throwable.printStackTrace();
        } finally {
            // 释放锁
            if(res){
                RedissLockUtil.unlock(Constants.DISTRIBUTED_REDIS_LOCK_KEY);
            }
        }
        return obj;

    }

}

public class RedissLockUtil {
    private static RedissonClient redissonClient;
    
    public void setRedissonClient(RedissonClient locker) {
    	redissonClient = locker;
    }
    
    /**
     * 加锁
     * @param lockKey
     * @return
     */
    public static RLock lock(String lockKey) {
    	RLock lock = redissonClient.getLock(lockKey);
    	lock.lock();
        return lock;
    }

    /**
     * 释放锁
     * @param lockKey
     */
    public static void unlock(String lockKey) {
    	RLock lock = redissonClient.getLock(lockKey);
		lock.unlock();
    }
    
    /**
     * 释放锁
     * @param lock
     */
    public static void unlock(RLock lock) {
    	lock.unlock();
    }

    /**
     * 带超时的锁
     * @param lockKey
     * @param timeout 超时时间   单位：秒
     */
    public static RLock lock(String lockKey, int timeout) {
    	RLock lock = redissonClient.getLock(lockKey);
		lock.lock(timeout, TimeUnit.SECONDS);
		return lock;
    }
    
    /**
     * 带超时的锁
     * @param lockKey
     * @param unit 时间单位
     * @param timeout 超时时间
     */
    public static RLock lock(String lockKey, TimeUnit unit ,int timeout) {
    	RLock lock = redissonClient.getLock(lockKey);
		lock.lock(timeout, unit);
		return lock;
    }
    
    /**
     * 尝试获取锁
     * @param lockKey
     * @param waitTime 最多等待时间
     * @param leaseTime 上锁后自动释放锁时间
     * @return
     */
    public static boolean tryLock(String lockKey, int waitTime, int leaseTime) {
        RLock lock = redissonClient.getLock(lockKey);
		try {
			return lock.tryLock(waitTime, leaseTime, TimeUnit.SECONDS);
		} catch (InterruptedException e) {
			return false;
		}
    }
    
    /**
     * 尝试获取锁
     * @param lockKey
     * @param unit 时间单位
     * @param waitTime 最多等待时间
     * @param leaseTime 上锁后自动释放锁时间
     * @return
     */
    public static boolean tryLock(String lockKey, TimeUnit unit, int waitTime, int leaseTime) {
    	RLock lock = redissonClient.getLock(lockKey);
		try {
			return lock.tryLock(waitTime, leaseTime, unit);
		} catch (InterruptedException e) {
			return false;
		}
    }

    /**
     * 初始红包数量
     * @param key
     * @param count
     */
    public void initCount(String key,int count) {
        RMapCache<String, Integer> mapCache = redissonClient.getMapCache("skill");
        mapCache.putIfAbsent(key,count,3,TimeUnit.DAYS);
    }
    /**
     * 递增
     * @param key
     * @param delta 要增加几(大于0)
     * @return
     */
    public int incr(String key, int delta) {
        RMapCache<String, Integer> mapCache = redissonClient.getMapCache("skill");
        if (delta < 0) {
            throw new RuntimeException("递增因子必须大于0");
        }
        return  mapCache.addAndGet(key, 1);//加1并获取计算后的值
    }

    /**
     * 递减
     * @param key 键
     * @param delta 要减少几(小于0)
     * @return
     */
    public int decr(String key, int delta) {
        RMapCache<String, Integer> mapCache = redissonClient.getMapCache("skill");
        if (delta < 0) {
            throw new RuntimeException("递减因子必须大于0");
        }
        return mapCache.addAndGet(key, -delta);//加1并获取计算后的值
    }
}

基于Zookeeper实现分布式锁

依赖

        <dependency>
            <groupId>org.apache.zookeeper</groupId>
            <artifactId>zookeeper</artifactId>
            <version>3.4.14</version>
        </dependency>

定义ZkLock

import lombok.extern.slf4j.Slf4j;
import org.apache.zookeeper.*;
import org.apache.zookeeper.data.Stat;

import java.io.IOException;
import java.util.Collections;
import java.util.List;

@Slf4j
public class ZkLock implements AutoCloseable, Watcher {

    private ZooKeeper zooKeeper;
    private String znode;

    public ZkLock() throws IOException {
        this.zooKeeper = new ZooKeeper("localhost:2181",
                10000,this);
    }

    public boolean getLock(String businessCode) {
        try {
            //创建业务 根节点
            Stat stat = zooKeeper.exists("/" + businessCode, false);
            if (stat==null){
                zooKeeper.create("/" + businessCode,businessCode.getBytes(),
                        ZooDefs.Ids.OPEN_ACL_UNSAFE,
                        CreateMode.PERSISTENT);
            }

            //创建瞬时有序节点  /order/order_00000001
            znode = zooKeeper.create("/" + businessCode + "/" + businessCode + "_", businessCode.getBytes(),
                    ZooDefs.Ids.OPEN_ACL_UNSAFE,
                    CreateMode.EPHEMERAL_SEQUENTIAL);

            //获取业务节点下 所有的子节点
            List<String> childrenNodes = zooKeeper.getChildren("/" + businessCode, false);
            //子节点排序
            Collections.sort(childrenNodes);
            //获取序号最小的（第一个）子节点
            String firstNode = childrenNodes.get(0);
            //如果创建的节点是第一个子节点，则获得锁
            if (znode.endsWith(firstNode)){
                return true;
            }
            //不是第一个子节点，则监听前一个节点
            String lastNode = firstNode;
            for (String node:childrenNodes){
                if (znode.endsWith(node)){
                    zooKeeper.exists("/"+businessCode+"/"+lastNode,true);
                    break;
                }else {
                    lastNode = node;
                }
            }
            synchronized (this){
                wait();
            }

            return true;

        } catch (Exception e) {
            e.printStackTrace();
        }
        return false;
    }





    @Override
    public void close() throws Exception {
        zooKeeper.delete(znode,-1);
        zooKeeper.close();
        log.info("我已经释放了锁！");
    }

    @Override
    public void process(WatchedEvent event) {
        if (event.getType() == Event.EventType.NodeDeleted){
            synchronized (this){
                notify();
            }
        }
    }
}

使用ZkLock

@RestController
@Slf4j
public class ZookeeperController {
    @Autowired
    private CuratorFramework client;

    @RequestMapping("zkLock")
    public String zookeeperLock(){
        log.info("我进入了方法！");
        try (ZkLock zkLock = new ZkLock()) {
            if (zkLock.getLock("order")){
                log.info("我获得了锁");
                Thread.sleep(10000);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } catch (Exception e) {
            e.printStackTrace();
        }
        log.info("方法执行完成！");
        return "方法执行完成！";
    }

}

基于curator实现分布式锁

依赖

        <dependency>
            <groupId>org.apache.curator</groupId>
            <artifactId>curator-recipes</artifactId>
            <version>4.2.0</version>
        </dependency>

启动类注入CuratorFramework

    @Bean(initMethod="start",destroyMethod = "close")
    public CuratorFramework getCuratorFramework() {
        RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3);
        CuratorFramework client = CuratorFrameworkFactory.newClient("localhost:2181", retryPolicy);
        return client;
    }

使用

@RestController
@Slf4j
public class ZookeeperController {
    @Autowired
    private CuratorFramework client;

    @RequestMapping("curatorLock")
    public String curatorLock(){
        log.info("我进入了方法！");
        // /order表示业务路径
        InterProcessMutex lock = new InterProcessMutex(client, "/order");
        try{
            if (lock.acquire(30, TimeUnit.SECONDS)){
                log.info("我获得了锁！！");
                Thread.sleep(10000);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            try {
                log.info("我释放了锁！！");
                lock.release();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        log.info("方法执行完成！");
        return "方法执行完成！";
    }
}

基于Redisson实现分布式锁(SpringBoot项目推荐用法)

依赖

        <dependency>
            <groupId>org.redisson</groupId>
            <artifactId>redisson-spring-boot-starter</artifactId>
            <version>3.17.2</version>
        </dependency>

配置redis

使用

@RestController
@Slf4j
public class RedissonLockController {
    @Autowired
    private RedissonClient redisson;

    @RequestMapping("redissonLock")
    public String redissonLock() {
        RLock rLock = redisson.getLock("order");
        log.info("我进入了方法！！");
        try {
            rLock.lock(30, TimeUnit.SECONDS);
            log.info("我获得了锁！！！");
            Thread.sleep(10000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }finally {
            log.info("我释放了锁！！");
            rLock.unlock();
        }
        log.info("方法执行完成！！");
        return "方法执行完成！！";
    }
}

基于Redisson实现分布式锁(通过xml配置)

依赖

        <dependency>
            <groupId>org.redisson</groupId>
            <artifactId>redisson</artifactId>
            <version>3.11.2</version>
        </dependency>

定义redisson.xml

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:redisson="http://redisson.org/schema/redisson"
       xsi:schemaLocation="
       http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans.xsd
       http://www.springframework.org/schema/context
       http://www.springframework.org/schema/context/spring-context.xsd
       http://redisson.org/schema/redisson
       http://redisson.org/schema/redisson/redisson.xsd
">

    <redisson:client>
        <!--单机模式-->
        <redisson:single-server address="redis://127.0.0.1:6379"/>
    </redisson:client>
</beans>

启动类上添加@ImportResource(“classpath*:redisson.xml”)

@SpringBootApplication
@ImportResource("classpath*:redisson.xml")
public class RedissonLockApplication {
    public static void main(String[] args) {
        SpringApplication.run(RedissonLockApplication.class, args);
    }
}

使用

@RestController
@Slf4j
public class RedissonLockController {
    @Autowired
    private RedissonClient redisson;

    @RequestMapping("redissonLock")
    public String redissonLock() {
        RLock rLock = redisson.getLock("order");
        log.info("我进入了方法！！");
        try {
            rLock.lock(30, TimeUnit.SECONDS);
            log.info("我获得了锁！！！");
            Thread.sleep(10000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }finally {
            log.info("我释放了锁！！");
            rLock.unlock();
        }
        log.info("方法执行完成！！");
        return "方法执行完成！！";
    }
}

多种分布式锁,我如何选择

推荐使用Redisson和Cutator实现分布式锁, 成熟,有大量的实践!

最后

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