Using JNA to get/set application identifier

Question

Following up on my previous question concerning the Windows 7 taskbar, I would like to diagnose why Windows isn't acknowledging that my application is independent of javaw.exe. I presently have the following JNA code to obtain the AppUserModelID:

public class AppIdTest {

    public static void main(String[] args) {
        NativeLibrary lib;
        try {
            lib = NativeLibrary.getInstance("shell32");
        } catch (Error e) {
            System.err.println("Could not load Shell32 library.");
            return;
        }
        Object[] functionArgs = new Object[1];
        String functionName = null;
        Function function;
        try {
            functionArgs[0] = new String("Vendor.MyJavaApplication")
                    .getBytes("UTF-16");
            functionName = "GetCurrentProcessExplicitAppUserModelID";
            function = lib.getFunction(functionName);
            // Output the current AppId
            System.out.println("1: " + function.getString(0));
            functionName = "SetCurrentProcessExplicitAppUserModelID";
            function = lib.getFunction(functionName);
            // Set the new AppId
            int ret = function.invokeInt(functionArgs);
            if (ret != 0) {
                Logger.out.error(function.getName() + " returned error code "
                        + ret + ".");
            }
            functionName = "GetCurrentProcessExplicitAppUserModelID";
            function = lib.getFunction(functionName);
            // Output the current AppId
            System.out.println("2: " + function.getString(0));
            // Output the current AppID, converted from UTF-16
            System.out.println("3: "
                    + new String(function.getByteArray(0, 255), "UTF-16"));
        } catch (UnsupportedEncodingException e) {
            System.err.println("System does not support UTF-16 encoding.");
        } catch (UnsatisfiedLinkError e) {
            System.err.println(functionName + " was not found in "
                    + lib.getFile().getName() + ".");
        }
    }
}

The output of the application is seemingly gibberish:

1: ‹ÿU‹ìƒìL¡¬Ÿv3ʼnEüSV‹uƒ&
2: ‹ÿU‹ìƒìL¡¬Ÿv3ʼnEüSV‹uƒ&
3: ????????????????P???????????

Being aware of the fact that the output may be UTF-16, in (3) I attempted to convert a byte array from UTF-16. In all honesty I don't know if my approach here is right as (a) I don't know the size of a PWSTR and (b) I don't know if GetCurrentProcessExplicitAppUserModelID is indeed returning a byte array or string.

I'm aware that JSmooth will run the GUI process in a wrapper which simulates this effect. Launch4j claims to do the same, but doesn't appear to work. I am looking to have the AppUserModelID set regardless of the Java wrapper.

What is going wrong here?

Answer 1

Hello Paul!

I didn't see your question before otherwise I would have given a try even without a bounty.

Here is what I came up with. Please note, as stated in the code itself, I didn't implement proper memory clean up with the CoTaskMemFree function (from Ole32.dll). So I suggest you take only the implementation for SetCurrentProcessExplicitAppUserModelID()

package com.stackoverflow.AppIdTest;

import com.sun.jna.Native;
import com.sun.jna.NativeLong;
import com.sun.jna.Pointer;
import com.sun.jna.WString;
import com.sun.jna.ptr.PointerByReference;

public class AppIdTest
{

  public static void main(String[] args) throws Exception
  {
    setCurrentProcessExplicitAppUserModelID(AppIdTest.class.getName());

    System.out.println(getCurrentProcessExplicitAppUserModelID());
  }

  // DO NOT DO THIS, IT'S JUST FOR TESTING PURPOSE AS I'M NOT FREEING THE MEMORY
  // AS REQUESTED BY THE DOCUMENTATION:
  //
  // http://msdn.microsoft.com/en-us/library/dd378419%28VS.85%29.aspx
  //
  // "The caller is responsible for freeing this string with CoTaskMemFree when
  // it is no longer needed"
  public static String getCurrentProcessExplicitAppUserModelID()
  {
    final PointerByReference r = new PointerByReference();

    if (GetCurrentProcessExplicitAppUserModelID(r).longValue() == 0)
    {
      final Pointer p = r.getValue();


      return p.getString(0, true); // here we leak native memory by lazyness
    }      
    return "N/A";
  }

  public static void setCurrentProcessExplicitAppUserModelID(final String appID)
  {
    if (SetCurrentProcessExplicitAppUserModelID(new WString(appID)).longValue() != 0)
      throw new RuntimeException("unable to set current process explicit AppUserModelID to: " + appID);
  }

  private static native NativeLong GetCurrentProcessExplicitAppUserModelID(PointerByReference appID);
  private static native NativeLong SetCurrentProcessExplicitAppUserModelID(WString appID);


  static
  {
    Native.register("shell32");
  }
}

Does it work for you?

At least here it correctly prints back:

com.stackoverflow.AppIdTest.AppIdTest