再做一个图像验证码，发现网上都是Servlet的生成代码，由于自己刚接触JSP和Servlet，对Session等功能不太熟，后台验证整了近一个小时，才明白生么意思，先把代码贴出来，共享一下。
//生成验证码
package djr.servlet;import java.awt.Color;import java.awt.Font;import java.awt.Graphics2D;import java.awt.image.BufferedImage;import java.io.IOException;import java.util.Random;import javax.servlet.ServletException;import javax.servlet.ServletOutputStream;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import com.sun.image.codec.jpeg.JPEGCodec;import com.sun.image.codec.jpeg.JPEGImageEncoder;public class IdentityServlet extends HttpServlet { /** * */ private static final long serialVersionUID = 1L; public static final char[] CHARS={'2','3','4','5','6','7','8','9','A','B','C','D','E','F','G','H','J','K','L','M','N','P','Q', 'R','S','T','U','V','W','X','Y','Z'}; public static Random random=new Random(); public static String getRandomString(){ StringBuffer buffer=new StringBuffer(); for(int i=0;i<6;i++){ buffer.append(CHARS[random.nextInt(CHARS.length)]); } return buffer.toString(); } public static Color getRandomColor(){ return new Color(random.nextInt(255),random.nextInt(255),random.nextInt(255)); } //返回某一颜色的反色 public static Color getReverseColor(Color c){ return new Color(255-c.getRed(),255-c.getGreen(),255-c.getBlue()); } public void doGet(HttpServletRequest request,HttpServletResponse response)throws ServletException,IOException{ doPost(request,response); } public void doPost(HttpServletRequest request,HttpServletResponse response)throws ServletException,IOException{ response.setHeader("Pragma", "No-cache"); response.setHeader("Cache-Control", "no-cache"); response.setDateHeader("Expires", 0); response.setContentType("image/jpeg"); String randomString=getRandomString(); int width=100; int height=30; Color color=getRandomColor(); Color reverse=getReverseColor(color); BufferedImage bi=new BufferedImage(width,height,BufferedImage.TYPE_INT_BGR); Graphics2D g=bi.createGraphics(); g.setFont(new Font(Font.SANS_SERIF,Font.BOLD,16)); g.setColor(color); g.fillRect(0, 0, width, height); g.setColor(reverse); g.drawString(randomString, 18, 20); for(int i=0,n=random.nextInt(100);i //主要是通过Session完成验证
System.out.println("后台验证验证码结果："+(String)request.getSession(true).getAttribute("randomString")); if(IdentityServlet.getRandomString()!=(String)request.getSession(true).getAttribute("randomString")){ url="index.jsp"; } else{ // 登录邮件系统 UserDTO userDTO = new UserDTO(); userDTO.setUserid(request.getParameter("txtUserID")); userDTO.setPassword(request.getParameter("pwdUserPWD")); Connection conn = DbFactory.getConnection(); UserDAO userDAO = new UserDAO(); if (userDAO.findUser(userDTO, conn)) { request.getSession().setAttribute("userinfo", userDTO); MailManager mailMgr = new MailManager(); mailMgr.setUser(userDTO.getUserid()); mailMgr.setPassword(userDTO.getPassword()); if (mailMgr.receiveMail()) { EmailDTO emailDTO = new EmailDTO(); emailDTO.setUserID(userDTO.getUserid()); List<EmailDTO> mailList = new EmailDAO().getMailList( emailDTO, conn); request.getSession().setAttribute("eMailList", mailList); } DbFactory.closeConn(conn); url = "main.jsp"; } else { url = "err.jsp"; } } } else if (url.toUpperCase().indexOf("LOGOUT") != -1) { // 退出邮件系统 request.getSession().invalidate(); url = "index.jsp"; } System.out.println(""+url); RequestDispatcher rd=request.getRequestDispatcher(url); rd.forward(request, response); } }希望看懂原理，代码不能直接Copy，我的是整个项目下的东西哦！红色标注的是关键！！！！