Handle external windows using java

Question

I need to check if an external window (another java program, but not controlled by the program that I'm working on) is open using the title, and if it open, then either maximize or minimize it based on the user command in Java (I know only the title of the window and nothing else) . Google only says that I can use winapi to get the window handle and manipulate it using the handle, but I'm not able to find how to do this.

I could find references on how to do it using JNI here: In Java Swing how do you get a Win32 window handle (hwnd) reference to a window?. Is it possible to do this without using JNI?

Could someone help me understand how to do this.

Thanks and Regards

Luke Quinane · Accepted Answer · 2011-07-13T00:25:13.390

20

I've just added a lot of win32 related window functions into JNA. You can see the details here.

// Find and minimize a window:
WinDef.HWND hWnd = User32.INSTANCE.FindWindow("className", "windowName");
User32.INSTANCE.ShowWindow(hWnd, WinUser.SW_MINIMIZE);

You can also enumerate all windows:

final WinDef.HWND[] windowHandle = new WinDef.HWND[1];
User32.INSTANCE.EnumWindows(new WinUser.WNDENUMPROC() {
    @Override
    public boolean callback(WinDef.HWND hwnd, Pointer pointer) {
        if (matches(hwnd)) {
            windowHandle[0] = hwnd;
            return false;
        }
        return true;
    }
}, Pointer.NULL);

// Minimize or maximize windowHandle[0] here...

edited Jul 13 '11 at 00:25

answered Jul 13 '11 at 00:12

Luke Quinane

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1

This is not related to winapi, but do you is something the same possible for Linux or MacOS? – Feb 10 '16 at 09:42
1

Here are some pointers for how to do this under Linux: http://stackoverflow.com/questions/5395044/embed-an-app-into-a-window It sounds like it might not be possible on Mac: http://stackoverflow.com/questions/3038288/how-to-reparent-a-cocoa-window – Luke Quinane Feb 12 '16 at 03:21

Bernd Elkemann · Answer 2 · 2011-07-12T14:19:26.097

2

You can use the Windows API to get a handle to the window and then resize it:

EnumWindows:
http://msdn.microsoft.com/en-us/library/ms633497%28v=VS.85%29.aspx

GetNextWindow:
http://msdn.microsoft.com/en-us/library/ms633509%28v=VS.85%29.aspx

GetWindowText:   (to decide whether that is the window you want; if title matches)
http://msdn.microsoft.com/en-us/library/ms633520%28v=VS.85%29.aspx

FindWindow:  (for this you need the exact title beforehand, not just part of it)
http://msdn.microsoft.com/en-us/library/ms633499%28v=vs.85%29.aspx

ShowWindow:
http://msdn.microsoft.com/en-us/library/ms633548%28v=VS.85%29.aspx

Typical WinAPI interface, a little clunky to use but powerful.

edited Jul 12 '11 at 14:19

answered Jul 12 '11 at 11:16

Bernd Elkemann

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+1 not possible without JNI, so either he uses JNI or he can't do it. – Aaron Digulla Jul 12 '11 at 13:52
Either way this method is overkill when there exists the FindWindow API – Mike Kwan Jul 12 '11 at 14:13

score 2 · Answer 3 · answered Jul 12 '11 at 13:51

2

Java has no API for this, so you have to use JNI. See eznme's answer for details.

answered Jul 12 '11 at 13:51

Aaron Digulla

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score 1 · Answer 4 · edited May 23 '17 at 12:10

As stated, this is not possible in pure Java. An example of doing it natively (which you would need to translate to JNI):

HWND hwnd = FindWindow( _T("classname"), _T("windowname") );

// Minimize
ShowWindow( hwnd, SW_MINIMIZE );

// Maximize
ShowWindow( hwnd, SW_MAXIMIZE );

You already have the window name but you should also supply a classname since this allows you to more accurately get the window. If there were multiple windows with the same windowname then your program might do something undesirable.

You can use something like Spy++ to get the class name. Or also simply through code. Ensure that your window is currently the only window with a matching windowname then you can do:

TCHAR lpClassName[256] = {0};

HWND hwnd = FindWindow( _T("classname"), _T("windowname") );
GetClassName( hwnd, lpClassName, _countof( lpClassName ) );
MessageBox( NULL, _T("Class Name"), lpClassName, MB_OK );

If it is possible to get the HWND from the Java process itself with the code here then you should pass that to the native part since it will be guaranteed to be reliable.

Handle external windows using java

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