基于Redis实现——分布式锁与实现

import redis.clients.jedis.Jedis;
import redis.clients.jedis.JedisPool;
import redis.clients.jedis.Transaction;
import redis.clients.jedis.exceptions.JedisException;import java.util.List;
import java.util.UUID;/**
* Created by liuyang on 2017/4/20.
*/
public class DistributedLock {
private final JedisPool jedisPool; public DistributedLock(JedisPool jedisPool) {
this.jedisPool = jedisPool;
} /**
* 加锁
* @param locaName 锁的key
* @param acquireTimeout 获取超时时间
* @param timeout 锁的超时时间
* @return 锁标识
*/
public String lockWithTimeout(String locaName,
long acquireTimeout, long timeout) {
Jedis conn = null;
String retIdentifier = null;
try {
// 获取连接
conn = jedisPool.getResource();
// 随机生成一个value
String identifier = UUID.randomUUID().toString();
// 锁名，即key值
String lockKey = "lock:" + locaName;
// 超时时间，上锁后超过此时间则自动释放锁
int lockExpire = (int)(timeout / 1000); // 获取锁的超时时间，超过这个时间则放弃获取锁
long end = System.currentTimeMillis() + acquireTimeout;
while (System.currentTimeMillis() < end) {
if (conn.setnx(lockKey, identifier) == 1) {
conn.expire(lockKey, lockExpire);
// 返回value值，用于释放锁时间确认
retIdentifier = identifier;
return retIdentifier;
}
// 返回-1代表key没有设置超时时间，为key设置一个超时时间
if (conn.ttl(lockKey) == -1) {
conn.expire(lockKey, lockExpire);
} try {
Thread.sleep(10);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
}
}
} catch (JedisException e) {
e.printStackTrace();
} finally {
if (conn != null) {
conn.close();
}
}
return retIdentifier;
} /**
* 释放锁
* @param lockName 锁的key
* @param identifier 释放锁的标识
* @return
*/
public boolean releaseLock(String lockName, String identifier) {
Jedis conn = null;
String lockKey = "lock:" + lockName;
boolean retFlag = false;
try {
conn = jedisPool.getResource();
while (true) {
// 监视lock，准备开始事务
conn.watch(lockKey);
// 通过前面返回的value值判断是不是该锁，若是该锁，则删除，释放锁
if (identifier.equals(conn.get(lockKey))) {
Transaction transaction = conn.multi();
transaction.del(lockKey);
List<Object> results = transaction.exec();
if (results == null) {
continue;
}
retFlag = true;
}
conn.unwatch();
break;
}
} catch (JedisException e) {
e.printStackTrace();
} finally {
if (conn != null) {
conn.close();
}
}
return retFlag;
}
}

import redis.clients.jedis.JedisPool;
import redis.clients.jedis.JedisPoolConfig;/**
* Created by liuyang on 2017/4/20.
*/
public class Service {
private static JedisPool pool = null; static {
JedisPoolConfig config = new JedisPoolConfig();
// 设置最大连接数
config.setMaxTotal(200);
// 设置最大空闲数
config.setMaxIdle(8);
// 设置最大等待时间
config.setMaxWaitMillis(1000 * 100);
// 在borrow一个jedis实例时，是否需要验证，若为true，则所有jedis实例均是可用的
config.setTestOnBorrow(true);
pool = new JedisPool(config, "127.0.0.1", 6379, 3000);
} DistributedLock lock = new DistributedLock(pool); int n = 500; public void seckill() {
// 返回锁的value值，供释放锁时候进行判断
String indentifier = lock.lockWithTimeout("resource", 5000, 1000);
System.out.println(Thread.currentThread().getName() + "获得了锁");
System.out.println(--n);
lock.releaseLock("resource", indentifier);
}
}

public class ThreadA extends Thread {
private Service service; public ThreadA(Service service) {
this.service = service;
} @Override
public void run() {
service.seckill();
}
}public class Test {
public static void main(String[] args) {
Service service = new Service();
for (int i = 0; i < 50; i++) {
ThreadA threadA = new ThreadA(service);
threadA.start();
}
}
}