OpenFileDialog

package nativedialogs;

import com.sun.jna.Native;
import com.sun.jna.WString;
import java.awt.Window;
import java.io.File;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import nativedialogs.ComDlg32JNA.ComDlg32;
import nativedialogs.ComDlg32JNA.ComDlg32.OPENFILENAME;

public class OpenFileDialog {

    private static final int MAX_BUF_SIZE = 64 * 1024;

    private OpenFileDialog() {
    }

    public static List<File> display(Window parent, boolean allowMultiSelect) {
        ByteBuffer buffer = ByteBuffer.allocateDirect(MAX_BUF_SIZE);
        buffer.order(ByteOrder.LITTLE_ENDIAN);
        OPENFILENAME ofn = new OPENFILENAME();

        ofn.lStructSize = ofn.size();
        ofn.lpstrFile = Native.getDirectBufferPointer(buffer);
        ofn.nMaxFile = MAX_BUF_SIZE;
        ofn.hwndOwner = parent == null
                ? null
                : Native.getWindowPointer(parent);
        ofn.Flags = ComDlg32.OFN_EXPLORER
                | ComDlg32.OFN_FILEMUSTEXIST
                | (allowMultiSelect ? ComDlg32.OFN_ALLOWMULTISELECT : 0);
        ofn.lpstrTitle = new WString("Hello world!");
        ofn.lpstrFilter = new WString("All files (*.*)\0*.*\0\0");

        boolean approved = ComDlg32.INSTANCE.GetOpenFileNameW(ofn);
        if (!approved) {
            int errCode = ComDlg32.INSTANCE.CommDlgExtendedError();
            if (errCode != 0) {
                throw new RuntimeException(String.format(
                        "GetOpenFileNameW failed. Error code: 0x%04X", errCode));
            }
            return null;
        }
        List<String> strings = extractNullSeparatedWideStrings(buffer);
        assert !strings.isEmpty();
        if (strings.size() == 1) {
            return Arrays.asList(new File(strings.get(0)));
        } else {
            List<File> files = new ArrayList<File>(strings.size() - 1);
            String dir = strings.get(0);
            for (String file : strings.subList(1, strings.size())) {
                files.add(new File(dir, file));
            }
            return files;
        }
    }

    private static List<String> extractNullSeparatedWideStrings(ByteBuffer buffer) {
        boolean lastWasNull = false;
        boolean foundTerminal = false;

        List<String> strings = new ArrayList<String>();
        StringBuilder sb = new StringBuilder();
        while (buffer.hasRemaining() && !foundTerminal) {
            char ch = buffer.getChar();
            if (ch != 0) {
                lastWasNull = false;
                sb.append(ch);
            } else if (lastWasNull) {
                foundTerminal = true;
            } else {
                lastWasNull = true;
                strings.add(sb.toString());
                sb.setLength(0);
            }
        }
        if (!foundTerminal) {
            throw new IllegalArgumentException("Buffer had no double NULL terminal");
        }
        return strings;
    }
}