关于基于Caffeine动态创建本地全局缓存的问题

这段代码写的有什么问题，求解！！！！

public class Caches {

    private Caches() {
    }

    private static class CacheUtil{
        private static final Caches CACHE = new Caches();
        private static final Map<String,String> KEY_MAP = new ConcurrentHashMap<>(  );
        private static final Map<String,Cache<String, Object>> CACHE_MAP = new ConcurrentHashMap<>(  );
    }

    public void put(String key,Object val,long duration, TimeUnit unit){
        String cacheKey = String.valueOf( unit ).concat( ":" ).concat( String.valueOf( duration ) );
        CacheUtil.KEY_MAP.put( key,cacheKey );
        CacheUtil.CACHE_MAP.putIfAbsent( cacheKey, Caffeine.newBuilder()
                .expireAfterWrite( duration, unit )
                .maximumSize(1000)
                .build());
        CacheUtil.CACHE_MAP.get( cacheKey ).put( key,val );
    }

    //默认1小时
    public void put(String key,Object val){
        long duration = 1000*60*60;
        TimeUnit unit = TimeUnit.MILLISECONDS;
        String cacheKey = String.valueOf( unit ).concat( ":" ).concat( String.valueOf( duration ) );
        CacheUtil.KEY_MAP.put( key,cacheKey );
        CacheUtil.CACHE_MAP.putIfAbsent( cacheKey, Caffeine.newBuilder()
                .expireAfterWrite( duration, unit )
                .maximumSize(1000)
                .build());
        CacheUtil.CACHE_MAP.get( cacheKey ).put( key,val );
    }

    public Object get(String key){
        if( null == CacheUtil.KEY_MAP.get( key )){
            return null;
        }
        return CacheUtil.CACHE_MAP.get( CacheUtil.KEY_MAP.get( key ) ).getIfPresent( key );
    }

    public static Caches buildCache(){
        return CacheUtil.CACHE;
    }
}

你先说说你遇到什么问题了吧，要不上来让别人帮你review代码？

https://blog.csdn.net/zhuyu19911016520/article/details/81946202