缓存 cache springcache

素颜马尾好姑娘i 2022-01-17 16:47 427阅读 0赞

[2019独角兽企业重金招聘Python工程师标准>>> ][2019_Python_] ![hot3.png][]

滑动过期:  每访问一次 过期时间往后延迟一次 即执行一次 redisTemplate.expire(provinceid,20000, TimeUnit.MILLISECONDS);

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@Cacheable(value = "province",
    key = "#root.targetClass.simpleName+':'+#root.methodName+':'+#provinceid")// value指定当前接口，要使用哪一个缓存器 --- 如果该缓存器不存在，则会自动创建  
    // 如果不指定key，spring将会自动将方法入参作为key

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//组合配置 同时更新两个缓存器中指定key的数据
    @Caching(put = {
            @CachePut(value = "province",key = "#entity.provinceid"),
            @CachePut(value = "city",key = "#entity.provinceid")}
    )
    public Provinces add(Provinces entity) {
        provincesDao.insert(entity);
        return entity;
    }

@CacheConfig(cacheNames="province") //通用配置 声明缓存器名称 即使此处不声明 在 @Cacheable(value = "province")时  将会被自动创建
    // 一旦声明了cacheNames 在使用@Cacheable时，则可以不指定value 如果配置了多个cacheName @CacheConfig(cacheNames={"province","city"}) 则相当于 @Cacheable(value //= {"province","city"})

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package com.enjoy.service;
    
    import com.enjoy.entity.Provinces;
    import org.slf4j.Logger;
    import org.slf4j.LoggerFactory;
    import org.springframework.cache.Cache;
    import org.springframework.cache.CacheManager;
    import org.springframework.stereotype.Service;
    
    import javax.annotation.Resource;
    import java.util.concurrent.ConcurrentHashMap;
    import java.util.concurrent.locks.Lock;
    import java.util.concurrent.locks.ReentrantLock;
    
    /**
     * 缓存雪崩  不能使用 @Cacheable
     */
    @Service("provincesService3")
    public class ProvincesServiceImpl3 extends ProvincesServiceImpl implements ProvincesService{
        private static final Logger logger = LoggerFactory.getLogger(ProvincesServiceImpl3.class);
        @Resource
        private CacheManager cm;
        private ConcurrentHashMap<String, Lock> locks = new ConcurrentHashMap<>();//线程安全的
    
        private static final String CACHE_NAME = "province";
        
        public Provinces detail(String provinceid) {
            // 1.从缓存中取数据
            Cache.ValueWrapper valueWrapper = cm.getCache(CACHE_NAME).get(provinceid);
            if (valueWrapper != null) {
                logger.info("缓存中得到数据");
                return (Provinces) (valueWrapper.get());
            }
    
            //2.加锁排队，阻塞式锁
            doLock(provinceid);//32个省，最多只有32把锁，1000个线程
            try{//第二个线程进来了
                // 一次只有一个线程
                 //双重校验，不加也没关系，无非是多刷几次库
                valueWrapper = cm.getCache(CACHE_NAME).get(provinceid);//第二个线程，能从缓存里拿到值？
                if (valueWrapper != null) {
                    logger.info("缓存中得到数据");
                    return (Provinces) (valueWrapper.get());//第二个线程，这里返回
                }
                Provinces provinces = super.detail(provinceid);
                // 3.从数据库查询的结果不为空，则把数据放入缓存中，方便下次查询
                if (null != provinces){
                    cm.getCache(CACHE_NAME).put(provinceid, provinces);
                }
                return provinces;
            }catch(Exception e){
                return null;
            }finally{
                //4.解锁
                releaseLock(provinceid);
            }
        }
    
        private void releaseLock(String userCode) {
            ReentrantLock oldLock = (ReentrantLock) locks.get(userCode);
            if(oldLock !=null && oldLock.isHeldByCurrentThread()){
                oldLock.unlock();
            }
        }
    
    
    
        private void doLock(String lockcode) {
    
            //provinceid有不同的值，参数多样化
            //provinceid相同的，加一个锁，---- 不是同一个key，不能用同一个锁
    
            ReentrantLock newLock = new ReentrantLock();//创建一个锁
    
            Lock oldLock = locks.putIfAbsent(lockcode, newLock);//若已存在，则newLock直接丢弃
            if(oldLock == null){
                newLock.lock();
            }else{
                oldLock.lock();
            }
        }
    }

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package com.enjoy.service;
    
    import com.enjoy.entity.Provinces;
    import com.google.common.base.Charsets;
    import com.google.common.hash.BloomFilter;
    import com.google.common.hash.Funnels;
    import org.springframework.cache.annotation.CacheEvict;
    import org.springframework.cache.annotation.CachePut;
    import org.springframework.cache.annotation.Cacheable;
    import org.springframework.stereotype.Service;
    import javax.annotation.PostConstruct;
    import java.util.List;
    
    /**
     * 缓存穿透
     */
    @Service("provincesService4")
    public class ProvincesServiceImpl4 extends ProvincesServiceImpl implements ProvincesService{
        private BloomFilter<String> bf =null; //等效成一个set集合
    
        @PostConstruct //对象创建后，自动调用本方法
        public void init(){//在bean初始化完成后，实例化bloomFilter,并加载数据
            List<Provinces> provinces = this.list();
            //当成一个SET----- 占内存，比hashset占得小很多
            bf = BloomFilter.create(Funnels.stringFunnel(Charsets.UTF_8), provinces.size());// 32个
            for (Provinces p : provinces) {
                bf.put(p.getProvinceid());
            }
        }
    
        @Cacheable(value = "province")
        public Provinces detail(String provinceid) {
            //先判断布隆过滤器中是否存在该值，值存在才允许访问缓存和数据库
            if(!bf.mightContain(provinceid)){
                System.out.println("非法访问--------"+System.currentTimeMillis());
                return null;
            }
            System.out.println("数据库中得到数据--------"+System.currentTimeMillis());
            Provinces provinces = super.detail(provinceid);
            return provinces;
        }
    
        @CachePut(value = "province",key = "#entity.provinceid")
        public Provinces update(Provinces entity) {
            super.update(entity);
            return entity;
        }
    
        @CacheEvict(value = "province",key = "#entity.provinceid")
        public Provinces add(Provinces entity) {
            super.add(entity);
            return entity;
        }
    
        @Override
        @CacheEvict("province")
        public void delete(String provinceid) {
            super.delete(provinceid);
        }
    }

转载于:https://my.oschina.net/u/2351011/blog/3059745

[2019_Python_]: https://my.oschina.net/u/2663968/blog/3061697
[hot3.png]: /images/20220114/f309a6a333c447788e6fd8f9819c6387.png
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