1\获取所有的缓存数据
NSURLCache *cache = [NSURLCache sharedURLCache];
2\获取某一request对应的缓存
NSCachedURLResponse *respose = [cache cachedResponseForRequest:request];
3\缓存有一属性NSData.通过response.data获取缓存数据
缓存NSCash
原文：http://www.cnblogs.com/making/p/5597678.html
