where to take L17bus to BCN T2 Barcelona

Could somebody please tell me where I can take L17 bus to Aeroport del Prat BCN airport T2 in Barcelona? I will get off my train in BARN.SANTS train station in 23:30. And then I need to take bus L17 to airport immediately. And also it's not safe to hang around at night in Barcelona. Sorry I can't enter Chinese. Hopefully someone can help me.