Via Infotype
TRY.
DATA(lo_employee_api) = cl_hcmfab_employee_api=>get_instance( ).
DATA(lv_pernr) = lo_employee_api->get_employeenumber_from_user( sy-uname ).
DATA(lv_ename) = lo_employee_api->get_name( lv_pernr ).
CATCH cx_hcmfab_common.
ENDTRY.
or via SU01
TRY.
DATA(lv_ename) = NEW /xiting/cl_su01_read( sy-uname )->get_fullname( ).
CATCH /xiting/cx_user.
ENDTRY.