以下是一个验证码的例子，w:drawImage的"draw"属性绑定后台的"draw"方法，该方法负责画图，最终图片就显示在客户端。

<w:drawImage width="60" height="20" draw="#{LoginBean.draw}">

LoginBean的代码：

@ManagedBean(scope = ManagedBeanScope.SESSION) 
public class LoginBean{
 
   ...... 

  public void draw(Graphics g, int width, int height) { 
    g.setColor(randColor(200, 250)); 
    g.fillRect(0, 0, width, height); 
    g.setFont(new Font("Times New Roman", Font.PLAIN, 18)); 
    g.setColor(randColor(160, 200)); 
    // 随机产生155条干扰线，使图像中的验证码不易被识别 
    for (int i = 0; i < 155; i++) { 
      int x = random.nextInt(width); 
      int y = random.nextInt(height); 
      int xl = random.nextInt(12); 
      int yl = random.nextInt(12); 
      g.drawLine(x, y, x + xl, y + yl); 
    } 
    // 将验证码显示在图像中 
    String code = randCode(); 
    for (int i = 0; i < 4; i++) { 
      g.setColor(randColor(20,130)); 
      g.drawString(code.substring(i,i+1), 13 * i + 6, 16); 
    } 
  } 

  ...... 

}