How can I keep a monster spawner spawning whilst I'm away? [duplicate]

I know that Minecraft spawn cages only spawn when you are near them, and the mob can spawn there naturally - but is there a way to keep them spawning? I need the spawner to work when I am away.

Without mods or editing the world using external tools, there is no way to keep a spawner active by yourself.

1. You could buy a second copy of Minecraft or have someone else join your world and stand next to your spawner.

2. By editing the world you can change the RequiredPlayerRange of the spawner so that it activates from a farther distance. This would generally be considered cheating for a survival world.

What I would recommend is to find ways to make better use of your time standing next to the spawner, by building things to work on there — equipment for crafting, potion brewing, etc. I've built a pool for fishing near one of my spawners, since that's something that also takes lots of time but also requires interaction. If you've got a particularly good setup like two spawners in the same area, maybe even build your base around them.