在 JFileChooser 中自定义 JPopupMenu：访问内部组件

import java.awt.*;
import java.util.Objects;
import java.util.stream.Stream;
import javax.swing.*;

public class FileChooserPopupMenuTest {
  public static void main(String[] args) {
    EventQueue.invokeLater(() -> {
      JFileChooser chooser = new JFileChooser();
      descendants(chooser)
          .filter(JPanel.class::isInstance)
          .map(c -> ((JPanel) c).getComponentPopupMenu())
          .filter(Objects::nonNull)
          .findFirst()
          .ifPresent(popup -> {
            popup.addSeparator();
            popup.add(new JCheckBoxMenuItem("JCheckBoxMenuItem"));
          });
      chooser.showOpenDialog(null);
    });
  }

  public static Stream<Component> descendants(Container parent) {
    return Stream.of(parent.getComponents())
        .filter(Container.class::isInstance)
        .map(Container.class::cast)
        .flatMap(c -> Stream.concat(Stream.of(c), descendants(c)));
  }
}