There are no limitations for JForex API. Any Dukascopy account can use it for free with no limitations.
A strategy can do whatever Java SE can do, hence, also use JNI or JNA. For instance (beforehand download the jna.jar file and put it in the respective directory):

@RequiresFullAccess
@Library("c:/temp/jna.jar")
public class StratMsgBoxJna implements IStrategy {

    public interface User32 extends com.sun.jna.Library {
        int MessageBoxA(int hwnd, String text, String caption, int flags);
        public int GetSystemMetrics(int nIndex);
    }

    @Override
    public void onStart(IContext context) throws JFException {
        User32 user32 = (User32) Native.loadLibrary("user32", User32.class);
        user32.MessageBoxA(0, "Hello JForex Strategy", "Test string from JForex Strategy", 1);
        context.getConsole().getOut().println("Screen resolution: " + user32.GetSystemMetrics(1) + " x " + user32.GetSystemMetrics(0));
    }