Java实现验证码的生成

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今天按组长要求，实现了前端登录界面验证码生成及识别功能，确保网站的安全性，无聊之余，总结今天的工作内容。下面是部分代码的讲解。

上图为前端代码，img标签里加入src的链接，CheckCodeAction.java为后台验证码的生成和验证。changImg()鼠标点击事件为调用后台CheckCodeAction生成验证码，打印到前端。changImg()事件的实现如下：

public class CheckCodeAction extends HttpServlet {

private Gson gson = new Gson();private HashMap<String, Object> map;public void doGet(HttpServletRequest request, HttpServletResponse response)        throws ServletException, IOException {    doPost(request, response);}public void doPost(HttpServletRequest request, HttpServletResponse response)        throws ServletException, IOException {    HttpSession session = request.getSession();    String checkcode = request.getParameter("checkcode");    String last_yzmcode = (String) session.getAttribute("yzmcode");    map = new HashMap<>();    if (checkcode != null) {        PrintWriter pw = response.getWriter();        if (checkcode.equalsIgnoreCase(last_yzmcode)) {            map.put("result", "OK");            String jstr = gson.toJson(map, HashMap.class);            pw.println(jstr);            return;        } else {            map.put("result", "ERROR");            String jstr = gson.toJson(map, HashMap.class);            pw.println(jstr);            return;        }    }    //告诉客户端，输出的格式    response.setContentType("image/jpeg");    response.setHeader("Pragma", "No-cache");    response.setHeader("Cache-Control", "no-cache");    response.setDateHeader("Expires", 0);    int width = 80;    int height = 40;    int lines = 7;    BufferedImage img = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);    Graphics g = img.getGraphics();    //设置背景色    g.setColor(Color.WHITE);    g.fillRect(0, 0, width, height);    //设置字体    g.setFont(new Font("黑体", Font.BOLD, 22));    //随机数字    Random r = new Random(new Date().getTime());    String yzmcode = "";    String str[] = {"0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"};    for (int i = 0; i < 4; i++) {        int a = r.nextInt(36);        int y = 20 + r.nextInt(10);//10~30范围内的一个整数，作为y坐标        String s = str[a];        Color c = new Color(r.nextInt(200), r.nextInt(200), r.nextInt(200));        g.setColor(c);        g.drawString("" + s, 5 + i * width / 4, y);        yzmcode += s;    }    //干扰线    for (int i = 0; i < lines; i++) {        Color c = new Color(r.nextInt(255), r.nextInt(255), r.nextInt(255));        g.setColor(c);        g.drawLine(r.nextInt(width), r.nextInt(height), r.nextInt(width), r.nextInt(height));    }    g.dispose();//类似于流中的close()带动flush()---把数据刷到img对象当中    ImageIO.write(img, "JPG", response.getOutputStream());    session.setAttribute("yzmcode", yzmcode);}

}

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