Java Stop Windows Shutdown

Question

I have a odd problem. I want to detect when windows wants to shutdown and stop it from shutting down using java. I thought about using a shutdown hook and just run a command shutdown /a however it doesnt seem to be working.

Answer 1

You need to respond to the WM_QUERYENDSESSION message and return 0.

You can do it with JNA.

Another example here: https://github.com/mirror/jdownloader/blob/master/src/org/jdownloader/osevents/windows/jna/ShutdownDetect.java

Answer 2

After battling with this problem few weeks and finally solving it i wanted to share the code here. Here is minimal example using java 1.8 and JNA 5.13.0 (also platform).

TIP: I had problem using this code first (unsatisfied links). I discovered i had library (jar file) on my JDK which had older JNA in it. Make sure you only have 1 version of JNA in your project.

import com.sun.jna.Native;
import com.sun.jna.platform.win32.WinDef.*;
import com.sun.jna.platform.win32.WinUser;
import com.sun.jna.platform.win32.WinUser.*;
import com.sun.jna.win32.W32APIOptions;
import com.sun.jna.platform.win32.User32;

public class RealShutdownBlocker {
private static final int WM_QUERYENDSESSION = 0x0011;

    public static void main(String[] args) {
        User32 user32 = Native.loadLibrary("user32", User32.class, W32APIOptions.DEFAULT_OPTIONS);

        WindowProc callback = new WindowProc() {
            public LRESULT callback(HWND hWnd, int message, WPARAM wParam, LPARAM lParam) {
                if (message == WM_QUERYENDSESSION) {
                    return new LRESULT(0);
                }
                return user32.DefWindowProc(hWnd, message, wParam, lParam);
            }
        };
        
        WNDCLASSEX windowClass = new WNDCLASSEX();
        windowClass.hInstance = null;
        windowClass.lpszClassName = "BlockShutdown";
        windowClass.lpfnWndProc = callback;
        user32.RegisterClassEx(windowClass);

        HWND hwnd = user32.CreateWindowEx(0, "BlockShutdown", "This prevents windows shutdown", WinUser.WS_OVERLAPPEDWINDOW, 100, 100, 640,
                480, null, null, null, null);

        // needs to be SW_SHOW for this to work
        user32.ShowWindow(hwnd, WinUser.SW_SHOW);

        MSG msg = new MSG();
        while (user32.GetMessage(msg, null, 0, 0) != 0) {
            user32.TranslateMessage(msg);
            user32.DispatchMessage(msg);
        }
    }
}

EDIT: No need for kernel32. Deleted it.