Hi,
Its called flexible netflow for the 3850 switches.
here is link on how to configure it:
http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3850/software/release/3se/flexible_netflow/configuration_guide/b_fnf_3se_3850_cg/b_fnf_3se_3850_cg_chapter_010.html
HTH