如何在自定义JTextField中绘制光标？

import javax.swing.*;
import java.awt.*;

public class CustomTextField extends JTextField {
    private int cursorPosition = 0; // 光标位置

    public CustomTextField() {
        super();
        setOpaque(false); // 设置背景透明
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g.create();

        // 绘制文本
        String text = getText();
        FontMetrics fm = g2d.getFontMetrics();
        int x = getInsets().left;
        int y = getHeight() - fm.getDescent();
        g2d.drawString(text, x, y);

        // 绘制光标
        int cursorWidth = fm.charWidth('a'); // 假设光标宽度为一个字符的宽度
        int cursorX = x + fm.stringWidth(text.substring(0, cursorPosition));
        g2d.setColor(Color.BLACK);
        g2d.fillRect(cursorX, getInsets().top, cursorWidth, getHeight() - getInsets().bottom);

        g2d.dispose();
    }

    @Override
    public void setCursorPosition(int position) {
        this.cursorPosition = position;
        repaint(); // 重绘组件以更新光标位置
    }

    public static void main(String[] args) {
        JFrame frame = new JFrame("Custom JTextField with Cursor");
        CustomTextField textField = new CustomTextField();
        frame.add(textField);
        frame.setSize(400, 100);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);

        // 模拟光标移动
        Timer timer = new Timer(500, e -> {
            int newPosition = (textField.getCursorPosition() + 1) % textField.getText().length();
            textField.setCursorPosition(newPosition);
        });
        timer.start();
    }
}