登录时候输入验证码，验证码图片从服务器获取方法.

import java.awt.Color; import java.awt.Font; import java.awt.Graphics; import java.awt.image.BufferedImage; import java.io.IOException; import java.io.PrintWriter; import java.util.Random; import javax.imageio.ImageIO; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class AuthCodeServlet extends HttpServlet { /** * Constructor of the object. */ public AuthCodeServlet() { super(); } /** * Destruction of the servlet. <br> */ public void destroy() { super.destroy(); // Just puts "destroy" string in log // Put your code here } /** * The doGet method of the servlet. <br> * * This method is called when a form has its tag value method equals to get. * * @param request the request send by the client to the server * @param response the response send by the server to the client * @throws ServletException if an error occurred * @throws IOException if an error occurred */ public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doPost(request,response); } /** * The doPost method of the servlet. <br> * * This method is called when a form has its tag value method equals to post. * * @param request the request send by the client to the server * @param response the response send by the server to the client * @throws ServletException if an error occurred * @throws IOException if an error occurred */ public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //判断类型是获取验证码图片 还是验证提交的验证码 String type = request.getParameter("type"); int trueFlag = 0; //代表是否验证通过 1验证码正确 0验证码错误 if("form".equals(type)){ String authCode = (String)request.getSession().getAttribute("authCode"); String code = request.getParameter("code"); if(authCode.equals(code)){ trueFlag = 1; }else{ trueFlag = 0; } }else if("generateAuthCode".equals(type)){ response.setHeader("Pragma", "No-cache"); response.setHeader("Cache-Control", "no-cache"); response.setDateHeader("Expires", 0L); int width = 60; int height = 20; BufferedImage image = new BufferedImage(width, height, 1); Graphics g = image.getGraphics(); Random random = new Random(); g.setColor(getRandColor(200, 250)); g.fillRect(0, 0, width, height); g.setFont(new Font("Times New Roman", 0, 18)); g.setColor(getRandColor(160, 200)); for (int i = 0; i < 155; 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); } String sRand = ""; for (int i = 0; i < 4; i++) { String rand = String.valueOf(random.nextInt(10)); sRand = sRand + rand; g.setColor(new Color(20 + random.nextInt(110), 20 + random.nextInt(110), 20 + random.nextInt(110))); g.drawString(rand, 13 * i + 6, 16); } //将验证码保存服务器session中 request.getSession().setAttribute("authCode", sRand); g.dispose(); try { //将图片写入输入流 ImageIO.write(image, "JPEG", response.getOutputStream()); } catch (Exception localException1) { } } try{ //跳转回页面 response.sendRedirect(request.getContextPath()+"/index.jsp?result="+trueFlag); }catch(Exception e){ } } 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); } /** * Initialization of the servlet. <br> * * @throws ServletException if an error occurs */ public void init() throws ServletException { // Put your code here } }