why spring redis session 'touch' method called in 'cleanExpiredSessions' method can clean expired session

Question

i am chinese,My English is so poor,I try my best to describe my problem clearly I recently learned about the spring redis session cleaning mechanism,the clean method is 'cleanExpiredSessions' in RedisSessionExpirationPolicy class,What makes me wonder is the 'touch(String key)' method can clean expire session,why? i think 'spring:session:sessions:d5e0f376-69d1-4fd4-9802-78eb5a3db144' expire time is fiveMinutesAfterExpires,when spring cleanup task runing,the key does not expired,so 'touch(String key)' method can not clean the key

Please explain to me thank you very much