<action name="Code" class="LoginAction" method="code">
<result name="success" type="stream">  
      <param name="contentType">image/jpeg</param> 
      <param name="inputName">inputStream</param>  
      <param name="bufferSize">2048</param>
</result></action>

private ByteArrayInputStream inputStream;　

 public ByteArrayInputStream getInputStream() {
return inputStream;
}
public void setInputStream(ByteArrayInputStream inputStream) {
this.inputStream = inputStream;
}

 public String code() throws Exception {
    
     int WIDTH = 60;
     int HEIGHT = 20;
    HttpServletResponse response = ServletActionContext.getResponse();

        // 设置浏览器不要缓存此图片
        response.setHeader("Pragma", "no-cache");

        response.setHeader("Cache-Control", "no-cache");

        response.setDateHeader("Expires", 0);

        String str = "0123456789qwertyuiopasdfghjklzxcvbnm";

        char[] rand = new char[4];

        Random random = new Random();

        for (int i = 0; i < 4; i++)
        {
            rand[i] = str.charAt(random.nextInt(36));
        }

        String rands =new String(rand);

        BufferedImage image = new BufferedImage(WIDTH, HEIGHT,BufferedImage.TYPE_INT_RGB);

        Graphics g = image.getGraphics();

        // 产生图像
        // 画背景
        g.setColor(new Color(0xDCDCDC));

        g.fillRect(0, 0, WIDTH, HEIGHT);

        // 随机产生 120 个干扰点

        for (int i = 0; i < 120; i++)
        {
            int x = (int) (Math.random() * WIDTH);

            int y = (int) (Math.random() * HEIGHT);

            int red = (int) (Math.random() * 255);

            int green = (int) (Math.random() * 255);

            int blue = (int) (Math.random() * 255);

            g.setColor(new Color(red, green, blue));

            g.drawOval(x, y, 1, 0);
        }

        g.setColor(Color.BLACK);

        g.setFont(new Font(null, Font.ITALIC | Font.BOLD, 18));

        // 在不同的高度上输出验证码的每个字符

        g.drawString("" + rands.charAt(0), 1, 17);

        g.drawString("" + rands.charAt(1), 16, 15);

        g.drawString("" + rands.charAt(2), 31, 18);

        g.drawString("" + rands.charAt(3), 46, 16);

        System.out.println(rands);

        // 结束图像 的绘制 过程， 完成图像
        g.dispose();

        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();

        ImageIO.write(image, "jpeg", outputStream);

        ByteArrayInputStream input = new ByteArrayInputStream(outputStream.toByteArray());

        this.setInputStream(input);

        HttpSession session = ServletActionContext.getRequest().getSession();

        session.setAttribute("checkCode", rands);
        
        input.close();
        
        outputStream.close();
return SUCCESS;    
    }

 <form id="form" action="Login.action" method="post">
    <table border=0 cellpadding="4">
    <tr><td><input type="text" name="username" placeholder="学号/工号/用户名" size="22" style="background-image: url(img/user.JPG);"><br></td></tr>
    <tr><td><input type="password" name="password" placeholder="密码" size="22" style="background-image: url(img/password.JPG);"><br></td></tr>
    <tr><td>
<input type="text" placeholder="验证码" name="checkCode" size="10"/>
<img alt="" src="Code.action" onclick="this.src='Code.action?'+ Math.random();" title="点击图片刷新验证码">
   </td> </tr>    
    <tr><td><input type="submit" class="btnCheck" value="登录" onclick="validate()" style="width:100%;"></button></td>
    </tr>
    </table>
    </form>

HttpSession session = ServletActionContext.getRequest().getSession();    
    String checkCode2 = (String)session.getAttribute("checkCode");
    System.out.println(checkCode+"aaa"+checkCode2);
    if(!checkCode.equals(checkCode2))
    {
    return "chekCodeerror";
    }