Hello, i've seen that a lot of players that have a spawner
don't really know how to handle with it.
So here is a simple guide of things i use myself.

First things first:
DO NEVER TRIE TO BREAK A SPAWNER!
Even if you have silk touch it will break and it will be gone.
You can change the type of monster of your spawner with the /spawner (monster) command.

How can i trap the mobs?
How can i deal with passive mobs and agresive mobs without replacing the spawner?
Here are 2 screenshots that explain the situations:

If you set it up this way it will be spawning passive mobs and agresive mobs.
The inside is 5x9x3, height doesn't matter exept if spawning enderman and of course higher then 1.
There is a 3x3 grass area around the spawner.
The spawner will only be 1 height block from the grass. (this was my first mistake, Thanks Luke(for helping))
At the two top sides there are two blocks, here will the water come.
You can make an iron door so the mobs can leave and you can enter. (not needed)

Here is water inside.
This way it will push mobs down the hole at the bottom of the image.
You can make a platform underneath it that will catch the drops of the mobs.
I would suggest 30 blocks underneath it.


Here are some self explaining screenshots:


Hope this helped you, peace out.
xita4

 

Uhm, /spawner command is like $25 donator+ you didn't write that in.

 

i dont even know how to get a spawner XD
i just use eggs and breed them and after that just kill

 

you have gamemode? i thought u were 25$ donor

 

He was single player creative get a closer look at the screen shots

 

Sorry i forgot to mention that you have to be a 25$ donor, or you can just buy a single spawner.
I don't have a gamemode it was creative and if you have cheats put on you can do /give (your name) 52.
The you will get a spawner.

 

why can i see a diamond sword down the hole at the second image?

 

That is the invisible notch

 

O_O
NOTCH in your savegame........

 

Yes, Notch is my father

 

Wouldn't the grass be removed since the water covers it?

 

hehehehehe mah zombie iron farm, :3

 

Yes it would, just keep an extra grass near it

 

I made some adjustments to mine, it's all cobble and I have grass blocks lined in the back so passive mobs can spawn...sometimes I use bait to make them come to me

 

so a spawner has to be above grass for anything to spawn?

 

Only for animals, not monsters.

 

hmmm might've wanted to check this out before putting my spawner on the ground, wasting all my grass and then accidentally breaking the spawner......:L

 

Dammit, wish I had a spawner...but good post

 

That is scary