Ok some people don't now how to do this but it's really easy

Step 1: Start Minecraft and go to your world.
Step 2: Take 1 or 2 or maybe 10 different items.
Step 3: Throw them on the ground.
Step 4: Close Minecraft ( really important ! )
Step 5: Open McEdit ( if you don't have it Google it! )
Step 6: Select the items. (the green things that is on the ground.
Step 7: Select the McEdit filter create spawner ( if you don't have it Google it! )
Step 8: Select the McEdit filter Change Spawner Properties ( if you don't have it Google it! )
Step 9: Save Your Stuff!!!!! ( Really important XD )
Step 10: Start Minecraft again and go to your world and enjoy.