How to keep Monsters Alive on Minecraft Creative Mode?

So I'm playing minecraft on creative mode, and I'm building a thing where I can keep an example of each one. (Creeper, skeleton, spider, zombie, slime, ghast, zombie pigman, enderman, cave spider, silvervish, blaze, magma cube, bat, witch, so on and so forth.) How can I keep them alive in a closed environment? Any help appreciated, I'm a noob to Minecraft.

Don't have direct lights within a certain radius near them, also be sure to change the difficulty, as peaceful despawns hostile mobs upon generation.