How to I access the data of a WMI Query (via JNA) SAFEARRAY result

问题

I use jna to run WMI queries. The following code queries WMI SELECT Caption,Capabilities from Win32_DiskDrive. The Type of Win32_DiskDrive.Capabilities is uint16[] and result.getValue returns a SAFEARRAY Instance.

System.out.println("Var Type(3 expected): " + value.getVarType().intValue());

returns randomly 0 or 3 if I start the process several times.

System.out.println("Size (>0 expected): " + (value.getUBound(0) - value.getLBound(0)));

is correct, but

Object el = value.getElement(0);

fails.

value.accessData();

returns null which is unexpected as well, so I cannot use OaIdlUtil#toPrimitiveArray (Nullpointer)

Unfortunately, the code does not work, and I have no idea what might be wrong. Any Ideas?

enum Win32_DiskDrive_Values {
        Caption,
        Capabilities
    }

    public static void main(String[] args) throws IOException, InterruptedException {
        try {
            WmiQuery<Win32_DiskDrive_Values> serialNumberQuery = new WmiQuery<Win32_DiskDrive_Values>("Win32_DiskDrive", Win32_DiskDrive_Values.class);
            Ole32.INSTANCE.CoInitializeEx(null, Ole32.COINIT_MULTITHREADED);
            WmiResult<Win32_DiskDrive_Values> result = serialNumberQuery.execute();
            for (int i = 0; i < result.getResultCount(); i++) {
                System.out.println(result.getValue(Win32_DiskDrive_Values.Caption, i));
                SAFEARRAY value = (SAFEARRAY) result.getValue(Win32_DiskDrive_Values.Capabilities, i);
                // According to https://docs.microsoft.com/en-us/windows/desktop/cimwin32prov/win32-diskdrive, the type of Capabilities
                // should be uint16[] which should be Variant.VT_I2 (2-byte integer)
                // however, it is not constant. sometimes it is 0, sometimes Variant.VT_I2 (3);
                System.out.println("Var Type(3 expected): " + value.getVarType().intValue());
                System.out.println("Size (>0 expected): " + (value.getUBound(0) - value.getLBound(0)));
                Object el = value.getElement(0);
                System.out.println("Element 0 (!=null expected): " + el);
                Pointer pointer = value.accessData();
                System.out.println("pointer (!=null expected): " + pointer);
            }
        } catch (Throwable e) {
            e.printStackTrace();
        } finally {
            Ole32.INSTANCE.CoUninitialize();
        }
    }

回答1:

The WMI code that I submitted to the JNA project is only set up to handle primitive values and Strings, not arrays. The problem you are encountering is that WMI is returning the pointer address to the array (either an empty array with VT_EMPTY = 0, or a 32-bit poniter with VT_I4 = 3). But the WMI result is released after the iteration, so you cannot use the WmiResult to fetch the object.

You need to write your own code (using the JNA implementation as a starting point) to grab the SAFEARRAY during iteration. You asked this question on the JNA website and @matthiasblaesing posted the following snippet which works for your use case:

public static void main(String[] args) throws IOException, InterruptedException {
    Ole32.INSTANCE.CoInitializeEx(null, Ole32.COINIT_MULTITHREADED);

    // Connect to the server
    Wbemcli.IWbemServices svc = WbemcliUtil.connectServer("ROOT\\CIMV2");

    // Send query
    try {
        Wbemcli.IEnumWbemClassObject enumerator = svc.ExecQuery("WQL", "SELECT Caption, Capabilities, CapabilityDescriptions FROM Win32_DiskDrive",
                Wbemcli.WBEM_FLAG_FORWARD_ONLY | Wbemcli.WBEM_FLAG_RETURN_IMMEDIATELY, null);

        try {
            IWbemClassObject[] result;
            VARIANT.ByReference pVal = new VARIANT.ByReference();
            IntByReference pType = new IntByReference();
            IntByReference plFlavor = new IntByReference();
            while(true) {
                result = enumerator.Next(0, 1);
                if(result.length == 0) {
                    break;
                }
                COMUtils.checkRC(result[0].Get("Caption", 0, pVal, pType, plFlavor));
                System.out.println("---------" + pVal.getValue() + "-------------");
                OleAuto.INSTANCE.VariantClear(pVal);
                COMUtils.checkRC(result[0].Get("CapabilityDescriptions", 0, pVal, pType, plFlavor));
                SAFEARRAY safeArray = (SAFEARRAY) pVal.getValue();
                for(int i = safeArray.getLBound(0); i<=safeArray.getUBound(0); i++) {
                    System.out.println("\t" + safeArray.getElement(i));
                }
                OleAuto.INSTANCE.VariantClear(pVal);
                COMUtils.checkRC(result[0].Get("Capabilities", 0, pVal, pType, plFlavor));
                safeArray = (SAFEARRAY) pVal.getValue();
                for(int i = safeArray.getLBound(0); i<=safeArray.getUBound(0); i++) {
                    System.out.println("\t" + safeArray.getElement(i));
                }
                OleAuto.INSTANCE.VariantClear(pVal);
                result[0].Release();
            }
        } finally {
            // Cleanup
            enumerator.Release();
        }
    } finally {
        // Cleanup
        svc.Release();
    }

    Ole32.INSTANCE.CoUninitialize();
}

来源：https://stackoverflow.com/questions/55651597/how-to-i-access-the-data-of-a-wmi-query-via-jna-safearray-result