G'Day,

I'm trying to intercept WM_POWERBROADCAST and WTS_SESSION_CHANGE mesages from a Java app. I'd prefer to do this using a hook, but I'd settle for subclassing WndProc() and processing messages if necessary.

I've had some success with the latter, using the code snippet below (my WTSAPI dll JNA interface omitted for brevity). And this approach seems to work fine until you lock/unlock or sleep/ restart a few times, after which the window hangs. Spy++ shows a whole bunch of WM_PAINT messages getting sent to my JFrame that apparently don't get processed. Any idea what I'm doing wrong?

I *have* gotten this code to receive messages when I change it to a system-wide global hook, but it tends to either crash the app, or, amusingly, causes a blue screen of death (presumably because hooking EVERY message in the system is a Really Bad Idea.

Any thoughts why my local hook isn't working here?

final User32 lib = User32.INSTANCE; HMODULE hMod = Kernel32.INSTANCE.GetModuleHandle(null); msgHook = new User32.CallWndRetProc() { public LRESULT callback(int nCode, WPARAM wParam, CWPRETSTRUCT info) {

if (nCode >= 0) { System.out.println("Got Message callback!"); } return lib.CallNextHookEx(hhk, nCode, wParam, info.getPointer()); } };

JFrame f = new JFrame(); f.pack(); f.setSize(100,100); f.setVisible(true);

swingThreadID = getSwingThreadID(); HINSTANCE threadLocalhMod = null; mhk = lib.SetWindowsHookEx(User32.WH_CALLWNDPROCRET, msgHook, threadLocalhMod, swingThreadID);

A few questions on hooking:

1. I suspect I'm using the wrong ThreadID (i've tried obtaining an ID from the Main thread and from the Swing worker thread, but neither work). Which Java thread receives the actual win32 Messages and how do I get its Thread ID?

2. The KeyHook example code starts a dummy messaging loop at the end to ensure it receives low level keyboard messages. If I start a JFrame in the same process, is this still necessary?

3. On SetWindowsHookEX and thread-local hooks, MSDN says "hMod [in]: Handle to the DLL containing the hook procedure pointed to by the lpfn parameter. The hMod parameter must be set to NULL if the dwThreadId parameter specifies a thread created by the current process and if the hook procedure is within the code associated with the current process. ". Is setting the third parameter in my call to a java null sufficient to achieve this?

Thanks in advance, Sam.

Oh yeah, and JNA rocks.