Java中分布式锁的不同实现,以及优缺点对比

Java中分布式锁的应用

本文只做引导,具体实现可能需要另行搜索
SQL | Redis | Zookeeper | Curator | Redisson 对比

数据库层级

1. 建立两个数据库,一个是业务库,一个是锁库
2. 正常些Service代码
3. 在锁库创建表, 字段是锁的名字
4. 利用怕他锁 select * from 表 where 锁的字段= 锁的名字 for update
5. 正常写代码

Redis

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;
    }

    public boolean unLock() {
        String script = "if redis.call(\"get\",KEYS[1]) == ARGV[1] then\n" +
                "    return redis.call(\"del\",KEYS[1])\n" +
                "else\n" +
                "    return 0\n" +
                "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;
    }


    @Override
    public void close() throws Exception {
        unLock();
    }
}


----------------
    ## 使用
    try (RedisLock redisLock = new RedisLock(redisTemplate,"redisKey",30)){
        if (redisLock.getLock()) {
            log.info("我进入了锁！！");
            Thread.sleep(15000);
        }
    } catch (InterruptedException e) {
        e.printStackTrace();
    } catch (Exception e) {
        e.printStackTrace();
    }

ZooKeeper

public class ZkLock implements Watcher,AutoCloseable {

    private ZooKeeper zooKeeper;
    private String businessName;
    private String znode;

    public ZkLock(String connectString,String businessName) throws IOException {
        this.zooKeeper = new ZooKeeper(connectString,30000,this);
        this.businessName = businessName;
    }

    public boolean getLock() throws KeeperException, InterruptedException {
        Stat existsNode = zooKeeper.exists("/" + businessName, false);
        if (existsNode == null){
            zooKeeper.create("/" + businessName,businessName.getBytes(),
                    ZooDefs.Ids.OPEN_ACL_UNSAFE,
                    CreateMode.PERSISTENT);
        }

        znode = zooKeeper.create("/" + businessName + "/" + businessName + "_", businessName.getBytes(),
                ZooDefs.Ids.OPEN_ACL_UNSAFE,
                CreateMode.EPHEMERAL_SEQUENTIAL);
        znode = znode.substring(znode.lastIndexOf("/")+1);
        List<String> childrenNodes = zooKeeper.getChildren("/" + businessName, false);
        Collections.sort(childrenNodes);
        String firstNode = childrenNodes.get(0);
        if (!firstNode.equals(znode)){
            String lastNode = firstNode;
            for (String node:childrenNodes){
                if (!znode.equals(node)){
                    lastNode = node;
                }else {
                    zooKeeper.exists("/"+businessName+"/"+lastNode,true);
                    break;
                }
            }
            synchronized (this){
                wait();
            }
        }
        return true;
    }

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


    @Override
    public void close() throws Exception {
        zooKeeper.delete("/"+businessName+"/"+znode,-1);
        zooKeeper.close();
    }
}

----------------
## 使用
 try (ZkLock zkLock = new ZkLock("localhost:2181","order")){
        if (zkLock.getLock()) {
            log.info("我进入了锁！！");
            Thread.sleep(15000);
        }
    } catch (InterruptedException e) {
        e.printStackTrace();
    } catch (Exception e) {
        e.printStackTrace();
    }

Curator

官网教程-超级简单

Redisson

官网教程-超级简单

优缺点对比

实现	优点	缺点
SQL	实现简单,容易理解	对数据库压力大
Redis	容易理解	不支持阻塞
Zookeeper	支持阻塞	需要了解ZK,程序复杂
Curator	提供现成锁的方法	依赖Zookeeper,强一致
Redisson	提供线程锁的方法