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public class VerificationControl {@GetMapping("/verification")@ResponseBodypublic void getVerificationControl(HttpServletRequest request, HttpServletResponse response, int width, int height) throws IOException {request.setCharacterEncoding("utf-8");response.setCharacterEncoding("utf-8");//1、生成数据String num = getNumbers();//2、生成照片BufferedImage bufferedImage = getPhoto(num, width,height);//3、将数据以会话的形式存储,只要会话没过期，就说明验证码有效,否则验证码不可以使用HttpSession session = request.getSession(true);//会话不存在创建会话//只要session对象获取成功,无论验证码是否过期 都要重新创建if(session!=null) {session.setMaxInactiveInterval(60 * 2);//验证码的最大存活时间session.setAttribute("Num", num);//4、设置不缓存照片response.setHeader("Pragma", "No-cache");response.setHeader("Cache-Control", "No-cache");response.setDateHeader("Expire", 0);//5、设置返回的数据格式response.setContentType("image/png");//6、图像输出到 输出字符流中 返回给前端ImageIO.write(bufferedImage, "png", response.getOutputStream());}}//获得随机字符串private String getNumbers() {char[] elem = new char[]{'A','B','C','D','E','F','G','H','I','G','K','L','M','N','O','P','Q','S','R','T','U','V','W','X','Y','Z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9'};StringBuilder res = new StringBuilder();Random random = new Random();for (int i = 0; i < 4; i++) {res.append(elem[random.nextInt(elem.length - 1)]);}return res.toString();}//获取照片private BufferedImage getPhoto(String num,int width,int height) throws IOException {
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