吃豆人-键盘事件如何获取焦点

如题，程序中键盘事件无法响应，怀疑是没有正确获取焦点，请问如何处理（程序功能是实现贪吃蛇自己自由自主移动，用户通过方向键改变方向）
代码附下：

import javax.swing.*;
import java.awt.*;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;

public class Draw extends Canvas implements InterfaceDefine{
    int a,b;
    int x,y;
    @Override
    public void paint(Graphics g) {
        draw.requestFocus(true);
        drawSnake(g);
        drawBean();
    }

    public void drawSnake(Graphics g){
        requestFocus(true);
        addKeyListener(new KeyAdapter() {
            @Override
            public void keyReleased(KeyEvent e) {
                if (e.getKeyCode() == KeyEvent.VK_UP ||
                        e.getKeyCode() == KeyEvent.VK_DOWN) {
                    System.out.println("ok");
                    a = 0;
                    if (e.getKeyCode() == KeyEvent.VK_DOWN) {
                        b = 10;
                    } else b = -10;
                }
                if (e.getKeyCode() == KeyEvent.VK_LEFT ||
                        e.getKeyCode() == KeyEvent.VK_RIGHT) {
                    b = 0;
                    System.out.println("ok");
                    if (e.getKeyCode() == KeyEvent.VK_RIGHT) {
                        a = 10;
                    } else a = -10;

                }
            }
        });
        g.fillRect(x++, y++, 10, 30);


    }

    public void drawBean(){
        Graphics g = this.getGraphics();
        g.fillOval(110,0,10,10);
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        update(g);


    }

}

使用requestFocus方法获取焦点。