java - Converting String to Pointer for JNA

Question

I'm trying to use JNA to query the effective permissions for a file in Windows. Eventually, I plan on using the GetEffectiveRightsFromAcl function, but to do so, I need to provide a pointer to a populated TRUSTEE structure. The JNA Platform (platform.jar) doesn't appear define this struct, so I'm trying to define it myself instead. Here's what I have so far:

public static class TRUSTEE extends Structure {
    public TRUSTEE() {
        super();
    }
    public TRUSTEE(Pointer p) {
        super(p);
        read();
    }

    public Pointer pMultipleTrustee;
    public int MultipleTrusteeOperation;
    public int TrusteeForm;
    public int TrusteeType;
    public Pointer ptstrName;
}

I'm trying to populate the structure like this:

private TRUSTEE createTrusteeForCurrentUser() {
    TRUSTEE result = new TRUSTEE();
    result.TrusteeForm = TRUSTEE_FORM.TRUSTEE_IS_NAME;
    result.TrusteeType = TRUSTEE_TYPE.TRUSTEE_IS_USER;

    String strName = "CURRENT_USER";
    // How can I set result.ptstrName using strName?
}

This Google Groups thread recommends using String fields in structures when a char * is called for. However, I don't think this is appropriate in my situation, considering the ptstrName field is allowed to point to different types of things, depending on the value of TrusteeForm. So, I think I somehow need to convert from String to Pointer instead. I found the NativeString class in JNA, which would work, except it's a package-private class.

What's the recommended way to convert a Java String to a native format and obtain a Pointer to it? Am I even using the right data type for the TRUSTEE struct? I'm somewhat new to JNA, so please excuse me if I'm missing something obvious.

Update

I found a solution to my problem, but if anyone has a better solution I'd still like to hear it.

Answer 1

Assuming you want char * on the native side (you may need more memory allocated if the string contains non-ascii characters),

String myString = "CURRENT_USER";
Pointer m = new Memory(myString.length() + 1); // WARNING: assumes ascii-only string
m.setString(0, myString); 

You can then use m wherever you need to reference the "native" string.

For wide strings (wchar_t *),

String myString = "CURRENT_USER";
Pointer m = new Memory(Native.WCHAR_SIZE * (myString.length() + 1));
m.setWideString(0, myString);