LoadingCache  
CacheBuilder.newBuilder()

常用参数
1. 缓存数据最大个数 CacheBuilder.maximumSize(long)
2. 过期时间 expireAfterAccess(long, TimeUnit) expireAfterWrite(long, TimeUnit)
3. 引用类型 CacheBuilder.weakKeys() CacheBuilder.weakValues() CacheBuilder.softValues()
4. 自动刷新  CacheBuilder.refreshAfterWrite
5. 过期时间  CacheBuilder.expireAfterWrite


load方法  不能返回  null , 
com.google.common.cache.CacheLoader$InvalidCacheLoadException: CacheLoader returned null for key 3

调用 recordStats()  才会 记录统计数据 ，否则都是0
Without this will return zero for all statistics


CacheStats{hitCount=14, missCount=21, loadSuccessCount=18, loadExceptionCount=3, totalLoadTime=43051592, evictionCount=6}

hitCount=14,
missCount=21
loadSuccessCount=18
loadExceptionCount=3
totalLoadTime=43051592
evictionCount=6


LoadingCache<Integer, String> cache = CacheBuilder.newBuilder()    		 
	    		// Without this will return zero for all statistics
	    		.recordStats()
                .maximumSize(7)
                // .refreshAfterWrite(3, TimeUnit.SECONDS)
                //软引用
                // .softValues() 
                .expireAfterWrite(3, TimeUnit.SECONDS)
                // .expireAfterAccess(duration, unit)
                .build(new CacheLoader<Integer, String>() {
                    @Override
                    public String load(Integer key) throws Exception {
                    	if(key>=3){
                    		// com.google.common.cache.CacheLoader$InvalidCacheLoadException: CacheLoader returned null for key 3
                    		//return null;
                    		return "NULL";
                    	}                   	
                	    SimpleDateFormat sdf = new SimpleDateFormat(DATEFORMAT);    	    
                        return key+"_"+sdf.format(new Date());
                    }
                });
                


完整代码
https://gitee.com/dyyx/demos/blob/master/guava/src/main/java/dyyx/CacheTest.java