Java笔记--验证码

生成验证码源文件

package cn.itcast.web.servlet; import java.awt.Color; import java.awt.Font; import java.awt.Graphics; import java.awt.image.BufferedImage; import java.io.IOException; import java.util.Random; import javax.imageio.ImageIO; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; /** * 验证码 */ @WebServlet("/CheckCodeServlet") public class CheckCodeServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException { //服务器通知浏览器不要缓存 response.setHeader("pragma","no-cache"); response.setHeader("cache-control","no-cache"); response.setHeader("expires","0"); //在内存中创建一个长80，宽30的图片，默认黑色背景 //参数一：长 //参数二：宽 //参数三：颜色 int width = 80; int height = 30; BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB); //获取画笔 Graphics g = image.getGraphics(); //设置画笔颜色为灰色 g.setColor(Color.GRAY); //填充图片 g.fillRect(0,0, width,height); //产生4个随机验证码，12Ey String checkCode = getCheckCode(); //将验证码放入HttpSession中 request.getSession().setAttribute("CHECKCODE_SERVER",checkCode); //设置画笔颜色为黄色 g.setColor(Color.YELLOW); //设置字体的小大 g.setFont(new Font("黑体",Font.BOLD,24)); //向图片上写入验证码 g.drawString(checkCode,15,25); //将内存中的图片输出到浏览器 //参数一：图片对象 //参数二：图片的格式，如PNG,JPG,GIF //参数三：图片输出到哪里去 ImageIO.write(image,"PNG",response.getOutputStream()); } /** * 产生4位随机字符串 */ private String getCheckCode() { String base = "0123456789ABCDEFGabcdefg"; int size = base.length(); Random r = new Random(); StringBuffer sb = new StringBuffer(); for(int i=1;i<=4;i++){ //产生0到size-1的随机值 int index = r.nextInt(size); //在base字符串中获取下标为index的字符 char c = base.charAt(index); //将c放入到StringBuffer中去 sb.append(c); } return sb.toString(); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { this.doGet(request,response); } }

验证验证码是否正确

//1. 设置编码 request.setCharacterEncoding("utf-8"); //2. 获取数据 String verifycode = request.getParameter("verifycode"); //3. 验证码校验 HttpSession session = request.getSession(); String checkcode_server = (String)session.getAttribute("CHECKCODE_SERVER"); if(!checkcode_server.equalsIgnoreCase(verifycode)){ //验证码不正确 //提示信息 //跳转登录页面 request.setAttribute("login_msg","验证码错误！"); request.getRequestDispatcher("/login.jsp").forward(request,response); return; }