Load from cache and refresh

// Builds an instance of Livebox using LiveboxBuilder class.
Livebox<UsersRes, Users> usersBox = new LiveboxBuilder<UsersRes, Users>()
                    .withKey("get_users")
                    .fetch(api::getUserList, UsersRes.class)
                    .addSource(Sources.MEMORY_LRU, ageValidator)
                    .addSource(Sources.DISK_PERSISTENT, persistentDiskValidator)
                    .addConverter(UsersRes.class, usersRes -> Optional.of(Users.fromUsersRes(usersRes)))
                    .retryOnFailure()
                    .refresh(true)
                    .build();