分布式系统定时任务，保证只有一个服务执行了改任务--采用redis分布式锁来实现（文章摘自：https://www.cnblogs.com/0201zcr/p/5942748.html）

文章摘自：https://www.cnblogs.com/0201zcr/p/5942748.html

package com.abtc.server.mine.common.utils;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.dao.DataAccessException;
import org.springframework.data.redis.connection.RedisConnection;
import org.springframework.data.redis.core.RedisCallback;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.serializer.StringRedisSerializer;

import java.util.UUID;

public class RedisLock
{
    private static Logger logger = LoggerFactory.getLogger(RedisLock.class);

    private RedisTemplate redisTemplate;

    private static final int DEFAULT_ACQUIRY_RESOLUTION_MILLIS = 10;

    // 记录当前获取锁的标识
    private String uuid = UUID.randomUUID().toString();

    /**
     * Lock key path.
     */
    private String lockKey;

    /**
     * 锁超时时间，防止线程在入锁以后，无限的执行等待
     */
    private int expireMsecs = 60 * 1000;

    /**
     * 锁等待时间，防止线程饥饿
     */
    private int timeoutMsecs = 10 * 1000;

    private volatile boolean locked = false;

    /**
     * Detailed constructor with default acquire timeout 10000 msecs and lock expiration of 60000 msecs.
     *
     * @param lockKey lock key (ex. account:1, ...)
     */
    public RedisLock(RedisTemplate redisTemplate, String lockKey)
    {
        this.redisTemplate = redisTemplate;
        this.lockKey = lockKey + "_lock";
        this.uuid = uuid;
    }

    /**
     * Detailed constructor with default lock expiration of 60000 msecs.
     */
    public RedisLock(RedisTemplate redisTemplate, String lockKey, int timeoutMsecs)
    {
        this(redisTemplate, lockKey);
        this.timeoutMsecs = timeoutMsecs;
    }

    /**
     * Detailed constructor.
     */
    public RedisLock(RedisTemplate redisTemplate, String lockKey, int timeoutMsecs, int expireMsecs)
    {
        this(redisTemplate, lockKey, timeoutMsecs);
        this.expireMsecs = expireMsecs;
    }

    /**
     * @return lock key
     */
    public String getLockKey()
    {
        return lockKey;
    }

    private String get(final String key)
    {
        Object obj = null;
        try
        {
            obj = redisTemplate.execute(new RedisCallback<Object>()
            {
                @Override
                public Object doInRedis(RedisConnection connection) throws DataAccessException
                {
                    StringRedisSerializer serializer = new StringRedisSerializer();
                    byte[] data = connection.get(serializer.serialize(key));
                    connection.close();
                    if (data == null)
                    {
                        return null;
                    }
                    return serializer.deserialize(data);
                }
            });
        }
        catch (Exception e)
        {
            logger.error("get redis error, key : {}", key);
        }
        return obj != null ? obj.toString() : null;
    }

    private boolean setNX(final String key, final String value)
    {
        Object obj = null;
        try
        {
            obj = redisTemplate.execute(new RedisCallback<Object>()
            {
                @Override
                public Object doInRedis(RedisConnection connection) throws DataAccessException
                {
                    StringRedisSerializer serializer = new StringRedisSerializer();
                    Boolean success = connection.setNX(serializer.serialize(key), serializer.serialize(value));
                    connection.close();
                    return success;
                }
            });
        }
        catch (Exception e)
        {
            logger.error("setNX redis error, key : {}", key);
        }
        return obj != null ? (Boolean) obj : false;
    }

    private String getSet(final String key, final String value)
    {
        Object obj = null;
        try
        {
            obj = redisTemplate.execute(new RedisCallback<Object>()
            {
                @Override
                public Object doInRedis(RedisConnection connection) throws DataAccessException
                {
                    StringRedisSerializer serializer = new StringRedisSerializer();
                    byte[] ret = connection.getSet(serializer.serialize(key), serializer.serialize(value));
                    connection.close();
                    return serializer.deserialize(ret);
                }
            });
        }
        catch (Exception e)
        {
            logger.error("setNX redis error, key : {}", key);
        }
        return obj != null ? (String) obj : null;
    }


    /**
     * 获得 lock.
     * 实现思路: 主要是使用了redis 的setnx命令,缓存了锁.
     * reids缓存的key是锁的key,所有的共享, value是锁的到期时间(注意:这里把过期时间放在value了,没有时间上设置其超时时间)
     * 执行过程:
     * 1.通过setnx尝试设置某个key的值,成功(当前没有这个锁)则返回,成功获得锁
     * 2.锁已经存在则获取锁的到期时间,和当前时间比较,超时的话,则设置新的值
     *
     * @return true if lock is acquired, false acquire timeouted
     * @throws InterruptedException in case of thread interruption
     */
    public synchronized boolean lock() throws InterruptedException
    {
        int timeout = timeoutMsecs;
        while (timeout >= 0)
        {
            long expires = System.currentTimeMillis() + expireMsecs + 1;
            String expiresStr = String.valueOf(expires) + "&" + uuid; //锁到期时间 + uuid
            if (this.setNX(lockKey, expiresStr))
            {
                // lock acquired
                locked = true;
                return true;
            }
            String currentValueStr = this.get(lockKey); //redis里的时间
            if (currentValueStr != null && !"".equals(currentValueStr))
            {
                String[] split = currentValueStr.split("&");
                if (split[0] != null && Long.parseLong(split[0]) < System.currentTimeMillis())
                {
                    // 判断是否为空，不为空的情况下，如果被其他线程设置了值，则第二个条件判断是过不去的
                    // lock is expired
                    String oldValueStr = this.getSet(lockKey, expiresStr);
                    // 获取上一个锁到期时间，并设置现在的锁到期时间，
                    // 只有一个线程才能获取上一个线上的设置时间，因为jedis.getSet是同步的
                    if (oldValueStr != null && oldValueStr.equals(currentValueStr))
                    {
                        // 防止误删（覆盖，因为key是相同的）了他人的锁——这里达不到效果，这里值会被覆盖，但是因为什么相差了很少的时间，所以可以接受

                        // [分布式的情况下]:如过这个时候，多个线程恰好都到了这里，但是只有一个线程的设置值和当前值相同，他才有权利获取锁
                        // lock acquired
                        locked = true;
                        return true;
                    }
                }
            }
            Thread.sleep(DEFAULT_ACQUIRY_RESOLUTION_MILLIS);
        }
        return false;
    }


    /**
     * Acqurired lock release.
     */
    public synchronized void unlock()
    {
        if (locked)
        {
            String keyValue = this.get(lockKey);
            if (keyValue != null && !"".equals(keyValue))
            {
                String[] split = keyValue.split("&");
                // 判断uuid是否已经被修改
                if (split.length == 2 && uuid.equals(split[1]))
                {
                    redisTemplate.delete(lockKey);
                }
            }
            locked = false;
        }
    }

}

　　

调用：

RedisLock lock = null;
try {
   //先获取状态，如果为Y则任务已经发送完毕
   if("Y".equals(redisutil.getString("flg"))){
       return;
   }
   lock = new RedisLock(redisTemplate, "flg",10000,20000);//这里的flg最终会变成flg_lock
   if(lock.lock()){
       //再次检索，因为有可能开始获取状态不是Y,但是在获取锁的过程中被别人置成Y，所以再次检索确保不重发
       if("Y".equals(redisutil.getString("flg"))){
          return;
       }
       redisutil.set("flg", "Y",300);
　　　　//======================================start
　　　　//执行自己需要的任务
　　　　//======================================end
　　}
} catch (Exception e) {
     e.printStackTrace();
}finally {
　　if(lock != null)
　　{lock.unlock();}

}

　　redisutil网上应该有很多，应该能搜到

注意：虽然可以实现我想要的效果，但是我个人有个疑问，分布式系统的时间是怎样统一的，如果时间不一样，可能会出问题