Created attachment 87475 [details]
Patch to FileChooserBuilder to implement this enhancement

The attached patch is a compatible addition to FileChooserBuilder adding the following interface
public interface SelectionApprover {
  public boolean approve (File[] selection);
}

which is called by the resulting JFileChooser's approveSelection() method if set to non-null, and the following methods
  public FileChooserBuilder addFileFilter (FileFilter filter);
  public FileChooserBuilder setSelectionApprover (SelectionApprover approver);

to FileChooserBuilder.  Would like fast-track API review for this, as it is a compatible addition which cannot cause any
regression, and enhances the usefulness of FileChooserBuilder.

Y01 No versioning info (@since, version increment, apichanges)
Y02 No test.

Created attachment 87798 [details]
Patch including apichanges, tests and spec version increment

Attached patch addresses Y01 and Y02.  Any other objections?

Fixed in core/main/ 25bf4adc5cb2

SelectionApprover does not seem to work as designed in single selection mode. When file chooser is shown using showOpenDialog, the SelectionApprover callback does not get the file selected in the array. See test below.

This is because FileShooserBuilder#approveSelection() method does this:

 boolean approved = approver.approve(getSelectedFiles());

and getFilesSelected() only returns files in multiple selection mode.

Or is there an alternative way of approving file selection for single-selection choosers?

    @Test
    public void testFileApprover() {
        FileChooserBuilder chooser = new FileChooserBuilder("");
        chooser.setTitle("Test");
        chooser.setSelectionApprover(new FileChooserBuilder.SelectionApprover() {
            @Override
            public boolean approve(File[] files) {
                DialogDisplayer.getDefault().notify(new NotifyDescriptor.Message("files to approve: " + files.length));
                return files.length > 0;
            }
        });
        chooser.showMultiOpenDialog(); // THIS WORKS
        chooser.showOpenDialog(); // THIS DOES NOT
    }