Need Memory Access if Possible

Question

Ok here is the deal, I am a developer for a small online game that was coded in Java. However being that it is java and very easy to decompile, I wanted to add an extra layer of security by having the client check the memory (and verify with the server) to make sure nothing is being modified by my users. Well that would be simple and easy if this was C/C++ but well this is java. I would prefer to not use JNI as that would introduce several separate pieces of code (Windows, Linux, Mac).
I have been finding bits and pieces about sun.misc.Unsafe to get access to memory, but I am having a hell of a time finding any type of documentation for that. I also wanted to see if there is another, preferably easier, way into the memory of my process.

Answer 1

Best thing to do is have the clients do as little as possible. Do ALL game logic on the server, and have it check whether the data sent by the client actually makes sense (for example someone running at 10 times the normal speed without some speed buff is obviously using a hacked client).
So the client just sends information like "I'm walking at normal speed in direction of 90 degrees", or "I'm casting spell ice of level 4 at mob located on (20,40)".
The server would validate whether the player can actually perform those actions, and send back position updates, success/failure of actions, etc. to the client.
If the client hacks anything, it's detected and he can be either ignored or blocked.