前台代码：
验证码
后台java代码：
public class CheckCodeAction { private ByteArrayInputStream inputStream; public void setInputStream(ByteArrayInputStream inputStream) { this.inputStream = inputStream; } public ByteArrayInputStream getInputStream() { return inputStream; } public String execute() throws Exception { // 在内存中创建图象 int width = 60, height = 20; BufferedImage image = new BufferedImage(width, height,BufferedImage.TYPE_INT_RGB); // 获取图形上下文 Graphics g = image.getGraphics(); // 生成随机类 Random random = new Random(); // 设定背景色 g.setColor(getRandColor(200, 250)); g.fillRect(0, 0, width, height); // 设定字体 g.setFont(new Font("Times New Roman", Font.PLAIN, 18)); // 随机产生60条干扰线，使图象中的认证码不易被其它程序探测到 g.setColor(getRandColor(160, 200)); for (int i = 0; i < 60; 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); } // 取随机产生的认证码(4位数字) String rand,sRand = "" ; for (int i = 0; i < 4; i++) { rand = String.valueOf(random.nextInt(10)); sRand += rand; // 将认证码显示到图象中 g.setColor(new Color(20 + random.nextInt(110), 20 + random.nextInt(110), 20 + random.nextInt(110))); // 调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成 g.drawString(rand, 13 * i + 6, 16); } // 将认证码存入SESSION HttpSession session = this.getSession(); session.setAttribute("rand", sRand); System.out.println(sRand); // 图象生效 g.dispose(); ByteArrayOutputStream output = new ByteArrayOutputStream(); ImageOutputStream imageOut = ImageIO.createImageOutputStream(output); ImageIO.write(image, "JPEG", imageOut); imageOut.close(); ByteArrayInputStream input = new ByteArrayInputStream(output.toByteArray()); this.setInputStream(input); return SUCCESS; } /* * 给定范围获得随机颜色 */ private Color getRandColor(int fc, int bc) { Random random = new Random(); 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); }} 配置文件：
image/jpeg inputStream