转：jianshu.com/p/91c1d5e059bd
1、缓存功能
redis.png
缓存设计主要问题：
缓存穿透；
缓存击穿；
缓存与数据库不一致；
缓存热点数据；
https://www.cnblogs.com/scholar-xie/p/7111132.html
http://www.cnblogs.com/codeon/p/8287563.html
https://www.cnblogs.com/codeon/p/8287582.html
2、计数
http://zhuanlan.51cto.com/art/201707/543851.htm
3、共享session
session.png
http://zhuanlan.51cto.com/art/201705/540250.htm
4、分布式限流
phoneNum = "138xxxxxxxx";
key = "shortMsg:limit:" + phoneNum; // SET key value EX 60 NX isExists = redis.set(key,1,"EX 60","NX"); if(isExists != null || redis.incr(key) <=5){ // 通过 }else{ // 限速 } https://www.cnblogs.com/softidea/p/6229543.html 令牌桶算法 5、分布式锁实现
@Service("distributedLockHandler")
public class DistributedLockHandler { private static final Integer Lock_Timeout = 3; @Autowired private RedisTemplate redisTemplate; private boolean innerTryLock(String lockKey){ JedisCmd jedisCmd = redisTemplate.getJedisCmd(); long currentTime = System.currentTimeMillis(); String lockTimeDuration = String.valueOf(currentTime + Lock_Timeout + 1); Long result = jedisCmd.setnx(lockKey, lockTimeDuration); if(result == 1){ return true; }else { if(checkIfLockTimeout(currentTime, lockKey)){//检查锁是否超时未释放 String preLockTimeDuration = jedisCmd.getSet(lockKey,lockTimeDuration);//利用getSet原子性。 //锁是否超时未释放，如果直接del key然后setnx key，当多个客户端使用时就后者就会覆盖前者操作。 if(currentTime > Long.valueOf(preLockTimeDuration)){ return true; } } return false; } } //获取锁 public boolean tryLock(String lockKey, Long timeout){ try{ Long currentTime = System.currentTimeMillis(); boolean result = false; while (true){ if((System.currentTimeMillis() - currentTime)/1000 > timeout){//获取超时 jobLog.info("Execute DistributedLockHandler.tryLock method, Time out."); break; }else { result = innerTryLock(lockKey); if(result){ break; }else {//重试 jobLog.debug("Try to get the Lock,and wait 100 millisecond...."); Thread.sleep(100); } } } return result; }catch (Exception e){ jobLog.error("Failed to run DistributedLockHandler.getLock method.", e); return false; } } //释放锁 public void realseLock(String lockKey){ JedisCmd jedisCmd = redisTemplate.getJedisCmd(); jedisCmd.del(lockKey); } //检查锁是否超时 public boolean checkIfLockTimeout(Long currentTime, String lockKey){ JedisCmd jedisCmd = redisTemplate.getJedisCmd(); if(currentTime > Long.valueOf(jedisCmd.get(lockKey))){ return true; }