In Java Swing how do you get a Win32 window handle (hwnd) reference to a window?

Question

In Java 1.4 you could use ((SunToolkit) Toolkit.getDefaultToolkit()).getNativeWindowHandleFromComponent() but that was removed.

It looks like you have to use JNI to do this now. Do you have the JNI code and sample Java code to do this?

I need this to call the Win32 GetWindowLong and SetWindowLong API calls, which can be done via the Jawin library.

I would like something very precise so I can pass a reference to the JDialog or JFrame and get the window handle.

Swing transparency using JNI may be related.

Answer 1

You don't have write any C/JNI code. From Java:

import sun.awt.windows.WComponentPeer;  public static long getHWnd(Frame f) {    return f.getPeer() != null ? ((WComponentPeer) f.getPeer()).getHWnd() : 0; } 

Caveats:

• This uses a sun.* package. Obviously this is not public API. But it is unlikely to change (and I think less likely to break than the solutions above).
• This will compile and run on Windows only. You would need to turn this into reflection code for this to be portable.

Answer 2

This little JNI method accepts a window title and returns the corresponding window handle.

JNIEXPORT jint JNICALL Java_JavaHowTo_getHwnd      (JNIEnv *env, jclass obj, jstring title){  HWND hwnd = NULL;  const char *str = NULL;   str = (*env)->GetStringUTFChars(env, title, 0);  hwnd = FindWindow(NULL,str);  (*env)->ReleaseStringUTFChars(env, title, str);  return (jint) hwnd;  } 

UPDATE:

With JNA, it's a little bit easier. I made a small example which find the handle and use it to bring the program to front.