Simple Url return cache

UrlCacheHelper.java

package com.extralam.utils;

import android.support.v4.util.LruCache;

/**
 * A Simple url return cache;
 */
public class UrlCacheHelper {

    private static final int CACHE_FACTOR = 8;
    private static final long FIXED_EXP_TIME = 60 * 1000 * 1;
    private static LruCache<String, CacheFork> sLocalCache;

    private static void createCache() {
        final int maxMemory = (int) (Runtime.getRuntime().maxMemory() / 1024);
        sLocalCache = new LruCache<String, CacheFork>(maxMemory/CACHE_FACTOR);
    }

    private static class CacheFork{
        long exptime = FIXED_EXP_TIME;
        long storeTime = 0;
        String mFile;
        public CacheFork(String file){
            storeTime = System.currentTimeMillis();
            mFile = file;
        }
        public CacheFork(String file , long _exptime){
            storeTime = System.currentTimeMillis();
            mFile = file;
            setExpTime(_exptime);
        }
        public void setExpTime(long _exptime){
            exptime = _exptime;
        }
    }


    public static void addCache(String url , String cache){
        if(sLocalCache == null){
            createCache();
        }
        sLocalCache.put(url, new CacheFork(cache));
    }

    public static void addCache(String url , String cache , long _exptime){
        if(sLocalCache == null){
            createCache();
        }
        sLocalCache.put(url, new CacheFork(cache, _exptime));
    }

    public static String getCache(String url){
        if(sLocalCache != null) {
            CacheFork obj = sLocalCache.get(url);
            if(obj == null || (System.currentTimeMillis() - obj.storeTime) > obj.exptime){
                sLocalCache.remove(url);
            }else{
                return obj.mFile;
            }
        }
        return null;
    }

    public static void clearCache(){
        if(sLocalCache != null) {
            sLocalCache.evictAll();
            sLocalCache = null;
        }
    }
    public static void clearHalfCache(){
        if(sLocalCache != null) {
            sLocalCache.trimToSize(sLocalCache.size() / 2);
        }
    }
}