Minecraft wiki entry for Hopper, associated text: Hopper + Item Frame = Item Filter - There is a request on the official feedback page for turning the combination of a hopper and an item frame into a filter.
Mods/Plugins for simpler sorters:
"HopperFilter 2.6" with Fuzzy filter option.
"Hopper Filter Vanilla-style Item Filters" with inverted filters (old MC versions only).