Minecraft wiki entry for Sweet_berry_farming, associated text: A stack of any solid building block such as cobblestone, planks, or terracotta.
A stack of dirt for planting the sweet berry bushes.
A minecart with hopper for transferring the berries to a hopper that itself transfers them to a storage block.
Rails for allowing the minecart to move under the dirt layer and collect the dropped berries.
Enough powered rails to make the minecart move infinitely.
A chest or barrel for storing the sweet berries that come from the hopper.
Blocks of redstone for activating the powered rails.
Foxes to harvest the sweet berry bushes, allowing them to be transferred to the minecart with hopper and then to the hopper and storage block, essentially powering the farm. Make sure to protect the foxes from wolves and polar bears.
A named farm animal to put in the area, or a clear view of the sky, to keep your foxes from falling asleep.