jsp页面该如何刷新验证码

（1）jsp代码：
换一换

（2）java代码（该代码为我自己框架代码，跟servlet写法不一样的我都给你注释了）：
public View authcode() throws IOException {
HttpServletResponse response = PuffContext.getResponse();//获取response
response.setContentType("image/jpeg");
response.setHeader("Pragma", "No-cache");
response.setHeader("Cache-Control", "no-cache");
response.setDateHeader("Expires", 0);
String authCode = AuthCodeUtil.getRandom(4); //获取验证码，代码在下面(3)
System.out.println("生成随机码：" + authCode);
PuffContext.getSession().setAttribute("session_authcode", authCode);//把该验证码存储在session
ServletOutputStream output = response.getOutputStream();
AuthCodeUtil.draw(output, authCode);
output.flush();
output.close();
return ViewFactory.nullView();//返回null
}

(3)///////////////////////////下面为生成验证码类////////////////////////////////////

public class AuthCodeUtil {
private final static Random random = new Random();
// 随机字体样式
private final static int[] fontStyle = { Font.HANGING_BASELINE, Font.ITALIC, Font.LAYOUT_LEFT_TO_RIGHT, Font.LAYOUT_NO_LIMIT_CONTEXT,
Font.LAYOUT_NO_START_CONTEXT, Font.LAYOUT_RIGHT_TO_LEFT };

/**
* 画随机码图
*
* @param out
* @param width
* @param height
* @throws IOException
*/
public static void draw(OutputStream out, String value) throws IOException {
int width = 80, height = 30;
BufferedImage bi = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
Graphics2D g = (Graphics2D) bi.getGraphics();
g.setColor(Color.WHITE);
g.fillRect(0, 0, width, height);
g.drawRect(1, 1, width - 2, height - 2);
for (int i = 0; i < 10; i++) {
g.setColor(randColor(150, 250));
g.drawOval(random.nextInt(110), random.nextInt(24), 5 + random.nextInt(10), 5 + random.nextInt(10));
}
int n = (int) (Math.random() * 6);
Font mFont = new Font("Arial", fontStyle[n], 23);
g.setFont(mFont);
g.setColor(randColor(10, 240));
g.drawString(value, 10, 21);// 随机数,水平距离,垂直距离
ImageIO.write(bi, "png", out);
}

private static Color randColor(int fc, int bc) {// 给定范围获得随机颜色
if (fc > 255)
fc = 255;
if (bc > 255)
bc = 255;
int r = fc + random.nextInt(bc - fc);
int g = fc + random.nextInt(bc - fc);
int b = fc + random.nextInt(bc - fc);
return new Color(r, g, b);
}

public static void main(String[] args) throws IOException {
FileOutputStream out = new FileOutputStream("d:\\aa.png");
draw(out, getRandom(4));
}

public static String getRandom(int size) {// 随机字符串
char[] c = { '1', '3', '5', '6', '7', '8', '9' };
StringBuffer sb = new StringBuffer();
for (int i = 0; i < size; i++)
sb.append(c[Math.abs(random.nextInt()) % c.length]);
return sb.toString();
}

}

我从头到尾说一遍吧

通过一个serlet绘制验证码，如DispCodeServlet

public class DispCodeServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {

  response.setHeader("Pragma", "No-cache");
  response.setHeader("Cache-Control", "no-cache");
  response.setDateHeader("Expires", 0);
  Random random=new Random();
  int length =5;
  String checkcode="";
  char code;
  int number;
  for(int i=0; i   number=random.nextInt(26);
   if(number%2==0)
    code=(char)('0'+(char)(number%10));
   else
    code=(char)('A'+(char)(number%26));
   checkcode+=code+"";
  }
  int width=(int)Math.ceil(length*12.5),height=22;
  BufferedImage image=new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);
  Graphics g=image.getGraphics();
  g.setColor(Color.WHITE);
  g.fillRect(0, 0, width, height);
  g.setColor(Color.GRAY);
  g.drawRect(0,0,width-1,height-1);
  for(int i=0;i<25;i++){
   int x1=random.nextInt(width);
   int y1=random.nextInt(height);
   int x2=random.nextInt(width);
   int y2=random.nextInt(height);
   g.setColor(Color.GRAY);
   g.drawLine(x1,y1,x2,y2);
  }
  g.setColor(Color.BLUE);
  g.setFont(new Font("Arial",Font.BOLD|Font.ITALIC,16));
  g.drawString(checkcode,5,18);
  HttpSession session=request.getSession();
  session.setAttribute("rand", checkcode);
  g.dispose();
  ImageIO.write(image, "JPEG", response.getOutputStream());
 }
 public void doPost(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {

  doGet(request,response);
 }
 }

在jsp页面中使用画验证码，如下

     src="DispCodeServlet">     onclick="refresh()">

然后在javascript中写入refresh()方法

function refresh() {
  document.getElementById("cc").src = "DispCodeServlet?a="
    + Math.random();
 }

验证码

imgcode.jsp就是输出的一个验证码， 然后changeCode是个js函数， 点一下就更换random_mark=1111 这个的值， 从而达到刷新的效果。希望采纳

this.src=你能访问到serlvet的路径；最好在这个路径的后面放一个随机数Math.random()；不需要接收这个参数，这只是告诉后台，这个路径跟你原来的是不一样的。