Pinning a Java application to the Windows 7 taskbar

Question

Original question

I use Launch4j as a wrapper for my Java application under Windows 7, which, to my understanding, in essence forks an instance of javaw.exe that in turn interprets the Java code. As a result, when attempting to pin my application to the task bar, Windows instead pins javaw.exe. Without the required command line, my application will then not run.

As you can see, Windows also does not realize that Java is the host application: the application itself is described as "Java(TM) Platform SE binary".

I have tried altering the registry key HKEY_CLASSES_ROOT\Applications\javaw.exe to add the value IsHostApp. This alters the behavior by disabling pinning of my application altogether; clearly not what I want.

After reading about how Windows interprets instances of a single application (and a phenomenon discussed in this question), I became interested in embedding a Application User Model ID (AppUserModelID) into my Java application.

I believe that I can resolve this by passing a unique AppUserModelID to Windows. There is a shell32 method for this, SetAppID(). (Or SetCurrentProcessExplicitAppUserModelID?) Is it possible to call it via JNI? If so, would this even resolve the issue?

On a side note, I was curious if any of the APIs discussed in this article could be implemented for a Java application.

Edit after implementing JNA, as Gregory Pakosz suggested

I've now implemented the following in an attempt to have my application recognized as a separate instance of javaw.exe:

NativeLibrary lib;
try {
    lib = NativeLibrary.getInstance("shell32");
} catch (Error e) {
    Logger.out.error("Could not load Shell32 library.");
    return;
}
Object[] args = { "Vendor.MyJavaApplication" };
String functionName = "SetCurrentProcessExplicitAppUserModelID";
try {
    Function function = lib.getFunction(functionName);
    int ret = function.invokeInt(args);
    if (ret != 0) {
        Logger.out.error(function.getName() + " returned error code "
                + ret + ".");
    }
} catch (UnsatisfiedLinkError e) {
    Logger.out.error(functionName + " was not found in "
            + lib.getFile().getName() + ".");
    // Function not supported
}

This appears to have no effect, but the function returns without error. Diagnosing why is something of a mystery to me. Any suggestions?

Working implementation

The final implementation that worked is the answer to my follow-up question concerning how to pass the AppID using JNA.

I had awarded the bounty to Gregory Pakosz' brilliant answer for JNI that set me on the right track.

Answer 1

SetCurrentProcessExplicitAppUserModelID (or SetAppID()) would in fact do what you're trying to do. However, it might be easier to modify your installer to set the AppUserModel.ID property on your shortcut - quoting from the Application User Model ID document mentioned above:

In the System.AppUserModel.ID property of the application's shortcut file. A shortcut (as an IShellLink, CLSID_ShellLink, or a .lnk file) supports properties through IPropertyStore and other property-setting mechanisms used throughout the Shell. This allows the taskbar to identify the proper shortcut to pin and ensures that windows belonging to the process are appropriately associated with that taskbar button. Note: The System.AppUserModel.ID property should be applied to a shortcut when that shortcut is created. When using the Microsoft Windows Installer (MSI) to install the application, the MsiShortcutProperty table allows the AppUserModelID to be applied to the shortcut when it is created during installation.

Answer 2

Try to use JSmooth. I use always this one. In JSmooth is there an option under Skeleton by Windowed Wrapper called

Lauch java app in exe process

See on this image.

Also command line arguments can be passed.
I think this can be a solution for you.

Martijn

Answer 3

I don't have Windows 7 but here is something that might get you started:

On the Java side:

package com.stackoverflow.homework;

public class MyApplication
{
  static void native setAppUserModelID();

  static
  {
    System.loadLibrary("MyApplicationJNI");
    setAppUserModelID();
  }
}

And on the native side, in the source code of the `MyApplicationJNI.dll library:

JNIEXPORT jboolean JNICALL Java_com_stackoverflow_howework_MyApplication_ setAppUserModelID(JNIEnv* env)
{
  LPCWSTR id = L"com.stackoverflow.homework.MyApplication";
  HRESULT hr = SetCurrentProcessExplicitAppUserModelID(id);

  return hr == S_OK;
}

Your question explicitly asked for a JNI solution. However, since your application doesn't need any other native method, jna is another solution which will save you from writing native code just for the sake of forwarding to the windows api. If you decide to go jna, pay attention to the fact that SetCurrentProcessExplicitAppUserModelID() is expecting a UTF-16 string.

When it works in your sandbox, the next step is to add operating system detection in your application as SetCurrentProcessExplicitAppUserModelID() is obviously only available in Windows 7:

• you may do that from the Java side by checking that System.getProperty("os.name"); returns "Windows 7".
• if you build from the little JNI snippet I gave, you can enhance it by dynamically loading the shell32.dll library using LoadLibrary then getting back the SetCurrentProcessExplicitAppUserModelID function pointer using GetProcAddress. If GetProcAddress returns NULL, it means the symbol is not present in shell32 hence it's not Windows 7.

EDIT: JNA Solution.

References:

• The JNI book for more JNI examples
• Java Native Access (JNA)

Answer 4

I have implemented access to the SetCurrentProcessExplicitAppUserModelID method using JNA and it works quite well when used as the MSDN documentation suggests. I've never used the JNA api in the way you have in your code snippet. My implementation follows the typical JNA usage instead.

First the Shell32 interface definition:

interface Shell32 extends StdCallLibrary {

    int SetCurrentProcessExplicitAppUserModelID( WString appID );

}

Then using JNA to load Shell32 and call the function:

final Map<String, Object> WIN32API_OPTIONS = new HashMap<String, Object>() {
    {
       put(Library.OPTION_FUNCTION_MAPPER, W32APIFunctionMapper.UNICODE);
       put(Library.OPTION_TYPE_MAPPER, W32APITypeMapper.UNICODE);
    }
};
Shell32 shell32 = (Shell32) Native.loadLibrary("shell32", Shell32.class,
           WIN32API_OPTIONS);
WString wAppId = new WString( "Vendor.MyJavaApplication" );
shell32.SetCurrentProcessExplicitAppUserModelID( wAppId );

Many of the API's in the last article you mentioned make use of Windows COM which is quite difficult to use directly with JNA. I have had some success creating a custom DLL to call these API's (eg. using the SHGetPropertyStoreForWindow to set a different app ID for a submodule window) which I then use JNA to access at runtime.