This server-only mod allows hoppers to have a whitelist filter, in order to let pass only items that are in the list.
The mod needs to be installed server-side only, or on the client for offline usage.
Filter is set by using a stick on any hopper. It will open a screen where items can be added or removed. The items will not be taken from the player's inventory.
When the filter is empty, the hopper will act just like in vanilla Minecraft.
