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

The following code lets you pass a Component to get the window handle (HWND) for it. To make sure that a Component has a corresponding window handle call isLightWeight() on the Component and verify that it equals false. If it doesn’t, try it’s parent by calling Component.getParent().

Java code:

package win32; public class Win32 {     public static native int getWindowHandle(Component c); } 

Header file main.h:

/* DO NOT EDIT THIS FILE - it is machine generated */ #include <jni.h> /* Header for class win32_Win32 */  #ifndef _Included_win32_Win32 #define _Included_win32_Win32 #ifdef __cplusplus extern 'C' { #endif /*  * Class:     win32_Win32  * Method:    getWindowHandle  * Signature: (Ljava/awt/Component;Ljava/lang/String;)I  */ JNIEXPORT jint JNICALL Java_win32_Win32_getWindowHandle   (JNIEnv *, jclass, jobject); #ifdef __cplusplus } #endif #endif 

The C source main.c:

#include<windows.h> #include <jni.h> #include <jawt.h> #include <jawt_md.h>  HMODULE _hAWT = 0;  JNIEXPORT jint JNICALL Java_win32_Win32_getWindowHandle   (JNIEnv * env, jclass cls, jobject comp) {     HWND hWnd = 0;     typedef jboolean (JNICALL *PJAWT_GETAWT)(JNIEnv*, JAWT*);     JAWT awt;     JAWT_DrawingSurface* ds;     JAWT_DrawingSurfaceInfo* dsi;     JAWT_Win32DrawingSurfaceInfo* dsi_win;     jboolean result;     jint lock;      //Load AWT Library     if(!_hAWT)         //for Java 1.4         _hAWT = LoadLibrary('jawt.dll');     if(!_hAWT)         //for Java 1.3         _hAWT = LoadLibrary('awt.dll');     if(_hAWT)     {         PJAWT_GETAWT JAWT_GetAWT = (PJAWT_GETAWT)GetProcAddress(_hAWT, '_JAWT_GetAWT@8');         if(JAWT_GetAWT)         {             awt.version = JAWT_VERSION_1_4; // Init here with JAWT_VERSION_1_3 or JAWT_VERSION_1_4             //Get AWT API Interface             result = JAWT_GetAWT(env, &awt);             if(result != JNI_FALSE)             {                 ds = awt.GetDrawingSurface(env, comp);                 if(ds != NULL)                 {                     lock = ds->Lock(ds);                     if((lock & JAWT_LOCK_ERROR) == 0)                     {                         dsi = ds->GetDrawingSurfaceInfo(ds);                         if(dsi)                         {                             dsi_win = (JAWT_Win32DrawingSurfaceInfo*)dsi->platformInfo;                             if(dsi_win)                             {                                 hWnd = dsi_win->hwnd;                             }                             else {                                 hWnd = (HWND) -1;                             }                             ds->FreeDrawingSurfaceInfo(dsi);                         }                         else {                             hWnd = (HWND) -2;                         }                         ds->Unlock(ds);                     }                     else {                         hWnd = (HWND) -3;                     }                     awt.FreeDrawingSurface(ds);                 }                 else {                     hWnd = (HWND) -4;                 }             }             else {                 hWnd = (HWND) -5;             }         }         else {             hWnd = (HWND) -6;         }     }     else {         hWnd = (HWND) -7;     }     return (jint)hWnd;  }