question: public < C extends Collection < T > , T > C retrieveCollection ( String key , Class < C > classCollection , Class < T > classData ) { key = safetyKey ( key ) ; try { File file = new File ( cacheDirectory , key ) ; Type typeCollection = jolyglot . newParameterizedType ( classCollection , classData ) ; T data = jolyglot . fromJson ( file , typeCollection ) ; return ( C ) data ; } catch ( Exception e ) { return null ; } }
target:  Retrieve a collection previously saved.