Java Swing - 如何使JFileChooser在用户所在的当前目录中打开

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.io.File;
import java.io.FileReader;

import javax.swing.AbstractAction;
import javax.swing.Action;
import javax.swing.JComponent;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JToolBar;
import javax.swing.border.EmptyBorder;

public class Main {
  JPanel gui = new JPanel(new BorderLayout());
  JFileChooser fileChooser;
  private JTextArea output = new JTextArea(10, 40);

  Main() {
    gui.setBorder(new EmptyBorder(2, 3, 2, 3));

    String userDirLocation = System.getProperty("user.dir");
    File userDir = new File(userDirLocation);
    // default to user directory
    fileChooser = new JFileChooser(userDir);

    Action open = new AbstractAction("Open") {
      @Override
      public void actionPerformed(ActionEvent e) {
        int result = fileChooser.showOpenDialog(gui);
        if (result == JFileChooser.APPROVE_OPTION) {
          try {
            File f = fileChooser.getSelectedFile();
            FileReader fr = new FileReader(f);
            output.read(fr, f);
            fr.close();
          } catch (Exception ex) {
            ex.printStackTrace();
          }
        }
      }
    };

    Action save = new AbstractAction("Save") {
      @Override
      public void actionPerformed(ActionEvent e) {
        int result = fileChooser.showSaveDialog(gui);
        System.out.println("Not supported yet.");
      }
    };

    JToolBar tb = new JToolBar();
    gui.add(tb, BorderLayout.PAGE_START);
    tb.add(open);
    tb.add(save);

    gui.add(new JScrollPane(output));
  }

  public JComponent getGui() {
    return gui;
  }

  public static void main(String[] args) {
    Main cicd = new Main();
    JFrame f = new JFrame("Chooser In Current Dir");
    f.add(cicd.getGui());
    f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
    f.pack();
    f.setVisible(true);
  }
}