验证码的变换

//验证码public String imageCode() throws IOException{//获得验证码随机数String code = ImageUtil1.getRandomCode(4);BufferedImage img = ImageUtil1.createImage(code);ValueStackUtil.setSessionAttribute("imgCode", code);ImageIO.write(img, "png", ServletActionContext.getResponse().getOutputStream());return null;}点击验证码变换<tr><td valign="middle" align="right">验证码:<img id="num" src="<s:url value='/user/user_imageCode'/>" onclick='this.src=this.src+"?c="+Math.random()'/></td><td valign="middle" align="left"><input id="code" type="text" required="true" class="inputgri" name="code" /></td></tr>点击换一张更换验证码<script type="text/javascript">function fun(){var img1 = document.getElementById("num");img1.src = "<s:url value='/user/user_imageCode'/>;" + new Date();          } </script><tr><td valign="middle" align="right">验证码:<img id="num" src="<s:url value='/user/user_imageCode'/>" /><a href="javascript:void(0)" onclick="fun()">换一张</a></td><td valign="middle" align="left"><input type="text" class="inputgri" name="code" /></td></tr>验证码的util方法：

public class ImageUtil {public static String getRandomCode(int n){String str = "1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";int len = str.length();StringBuffer sb = new StringBuffer();Random r = new Random();for(int i=0;i<n;i++){sb.append(str.charAt(r.nextInt(len)));}return sb.toString();} public static BufferedImage createImage(String securityCode){        int codeLength = securityCode.length();//验证码长度        int fontSize = 20;//字体大小        int fontWidth = fontSize+1;        //图片宽高        int width = codeLength*fontWidth+60;        int height = fontSize*2;        //图片        BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);        Graphics2D g = image.createGraphics();        g.setColor(Color.WHITE);//设置背景色        g.fillRect(0, 0, width, height);//填充背景        g.setColor(Color.LIGHT_GRAY);//设置边框颜色        g.setFont(new Font("Courier New", Font.BOLD, height-2));//边框字体样式        g.drawRect(0, 0,0, 0);//绘制边框        //绘制噪点        Random rand = new Random();        g.setColor(Color.LIGHT_GRAY);        for (int i = 0; i < codeLength*6; i++) {            int x = rand.nextInt(width);            int y = rand.nextInt(height);            g.drawRect(x, y, 1, 1);//绘制1*1大小的矩形        }        //绘制验证码        int codeY = height-10;        g.setColor(new Color(19,148,246));        g.setFont(new Font("Georgia", Font.BOLD, fontSize));        for(int i=0;i<codeLength;i++){        double deg=new Random().nextDouble()*20;        g.rotate(Math.toRadians(deg), i*16+13,codeY-7.5);            g.drawString(String.valueOf(securityCode.charAt(i)), i*16+5, codeY);            g.rotate(Math.toRadians(-deg), i*16+13,codeY-7.5);        }               g.dispose();//关闭资源        return image;    }}