java应用本地缓存

public class LiveCache<T> {
    // 缓存时间
    private final int cacheMillis;
    // 缓存对象
    private final T element;
    // 缓存对象创建时间
    private final long createTime;
 
    public LiveCache(int cacheMillis, T element) {
        this.cacheMillis = cacheMillis;
        this.element = element;
        this.createTime = System.currentTimeMillis();
    }
 
    // 获取缓存对象
    public T getElement() {
        long currentTime = System.currentTimeMillis();
        if(cacheMillis > 0 && currentTime - createTime > cacheMillis) {
            return null;
        } else {
            return element;
        }
    }
 
    // 获取缓存对象，忽略缓存时间有效性
    public T getElementIfNecessary() {
        return element;
    }
}
 
public static void main(String[] args) {
    int cacheMilis = 1000 ;
    LiveCache<Object> liveCache = new LiveCache<>(cacheMilis, new Object()) ;
 
    liveCache.getElement() ;
    liveCache.getElementIfNecessary() ;
 
}

@FunctionalInterface
public interface LiveFetch<T> {
    // 刷新缓存接口
    T fetch() ;
}
 
public class LiveManager<T> {
    // 缓存时间
    private int cacheMillis;
    // 缓存对象
    private LiveCache<T> liveCache;
    // 刷新缓存的对象
    private LiveFetch<T> liveFetch ;
 
    private Logger logger = LoggerFactory.getLogger(LiveManager.class) ;
 
    // 刷新缓存开关
    private boolean refresh = false ;
 
    public LiveManager(int cacheMillis, LiveFetch<T> liveFetch) {
        this.cacheMillis = cacheMillis ;
        this.liveFetch = liveFetch ;
    }
 
    /**
     * fetch cache ; if cache expired , synchronous fetch
     * @return
     */
    public T getCache() {
 
        initLiveCache();
 
        if(liveCache != null) {
            T t  ;
            if((t= liveCache.getElement()) != null) {
                return t ;
            } else {
                t = liveFetch.fetch() ;
                if(t != null) {
                    liveCache = new LiveCache<T>(cacheMillis, t) ;
                    return t ;
                }
            }
        }
 
        return null ;
    }
 
    /**
     * fetch cache ; if cache expired , return old cache and asynchronous fetch
     * @return
     */
    public T getCacheIfNecessary() {
 
        initLiveCache();
 
        if(liveCache != null) {
            T t  ;
            if((t= liveCache.getElement()) != null) {
                return t ;
            } else {
                refreshCache() ;
                return liveCache.getElementIfNecessary() ;
            }
        }
 
        return null ;
    }
 
    /**
     * init liveCache
     */
    private void initLiveCache() {
        if(liveCache == null) {
            T t = liveFetch.fetch() ;
            if(t != null) {
                liveCache = new LiveCache<T>(cacheMillis, t) ;
            }
        }
    }
 
    /**
     * asynchronous refresh cache
     */
    private void refreshCache() {
 
        if(refresh)
            return ;
        refresh = true ;
        try {
            Thread thread = new Thread(() -> {
                try {
                    T t = liveFetch.fetch();
                    if (t != null) {
                        liveCache = new LiveCache<>(cacheMillis, t);
                    }
                } catch (Exception e){
                    logger.error("LiveManager.refreshCache thread error.", e);
                } finally {
                    refresh = false ;
                }
            }) ;
            thread.start();
        } catch (Exception e) {
            logger.error("LiveManager.refreshCache error.", e);
        }
    }
}
 
public class Test {
 
    public static void main(String[] args) {
        int cacheMilis = 1000 ;
        LiveManager<Object> liveManager = new LiveManager<>(cacheMilis,() -> new Test().t1()) ;
 
        liveManager.getCache() ;
        liveManager.getCacheIfNecessary() ;
    }
 
    public Object t1(){
 
        return new Object() ;
    }
}