See for the reason why http://www.jmonkeyengine.com/jmeforum/index.php?topic=10850.0
Here the two classes:
DummyKeyInput
/*
* Copyright (c) 2003-2009 jMonkeyEngine
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* met:
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* without specific prior written permission.
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package com.jme.input.dummy;
import java.util.Arrays;
import java.util.logging.Level;
import java.util.logging.Logger;
import org.lwjgl.input.Keyboard;
import org.lwjgl.opengl.Display;
import com.jme.input.KeyInput;
import com.jme.input.KeyInputListener;
/**
* <code>DummyKeyInput</code> simulates a Keyinput system, useable for Applications that can be headless or not.
* @author Kai B