Servlet 实现随机验证码
摘要： 网页上的表单经常需要用到验证码，验证码是以图片的形式显示的，图片由后台Servlet生成，通过URI链接显示在网页上。
首先说明一下随机验证码的流程。
从流程图可以看出，我们需要做一下几步工作。
- 通过后台Servlet生成随机图片。
- 创建Session会话，并通过登录页面进行验证。
- 刷新随机图片超链接后，更换验证码图片。
/** * To change this template, choose Tools | Templates * and open the template in the editor. */ package net.individuals.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; /** * * @author Barudisshu */ @WebServlet(name = "ImageCodeMakerServlet", urlPatterns = {"/ImageCodeMakerServlet"}) public class ImageCodeMakerServlet extends HttpServlet { /** * Processes requests for both HTTP * <code>GET</code> and * <code>POST</code> methods. * * @param request servlet request * @param response servlet response * @throws ServletException if a servlet-specific error occurs * @throws IOException if an I/O error occurs */ protected void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //设置页面不缓存 response.setHeader("Pragma", "No-cache"); response.setHeader("Cache-Control", "No-cache"); //设置有效期 response.setDateHeader("Expires", 0); //设置图片的宽度和高度 int width = 60, height = 20; //创建一个图像对象 BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB); //获取画图对象 Graphics g = image.createGraphics(); //创建随机对象 Random random = new Random(); //用随机颜色填充图像背景 g.setColor(new Color(255, 255, 255)); //图像形状 g.fillRect(0, 0, width, height); //设置字体 g.setFont(new Font("Tahoma", Font.PLAIN, 20)); //随机数字符串 String sRand = ""; for (int i = 0; i < 4; i++) { //生成四个数字字符 String rand = String.valueOf(random.nextInt(10)); sRand += rand; //生成随机颜色 g.setColor(new Color(100 + random.nextInt(155), random.nextInt(100), 100 + random.nextInt(155))); //将随机数字画在图像上 g.drawString(rand, (12 + random.nextInt(2)) * i + 6, 18); } //生成干扰线 for (int k = 0; k < 24; k++) { g.setColor(getRandomColor(0, 255)); int x = random.nextInt(width); int y = random.nextInt(height); int x1 = random.nextInt(6); int y1 = random.nextInt(6); g.drawLine(x, y, x + x1, y + y1); } //生成干扰像素点 for (int i = 0; i < 10; i++) { g.setColor(getRandomColor(50, 180)); int x = random.nextInt(width); int y = random.nextInt(height); g.drawOval(x, y, 1, 1); } //将生成的随机数字写入Session会话 request.getSession().setAttribute("randcode", sRand); //使图像生效 g.dispose(); //输出图像到页面 ImageIO.write(image, "JPEG", response.getOutputStream()); } /** * 产生一个随机颜色 * * @param fc 颜色分量最小值 * @param bc 颜色分量最大值 * @return */ public Color getRandomColor(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); } // <editor-fold defaultstate="collapsed" desc="HttpServlet methods. Click on the + sign on the left to edit the code."> /** * Handles the HTTP * <code>GET</code> method. * * @param request servlet request * @param response servlet response * @throws ServletException if a servlet-specific error occurs * @throws IOException if an I/O error occurs */ @Override protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { processRequest(request, response); } /** * Handles the HTTP * <code>POST</code> method. * * @param request servlet request * @param response servlet response * @throws ServletException if a servlet-specific error occurs * @throws IOException if an I/O error occurs */ @Override protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { processRequest(request, response); } /** * Returns a short description of the servlet. * * @return a String containing servlet description */ @Override public String getServletInfo() { return "Short description"; }// </editor-fold> } 实现点击图片更新随机验证码。需要在URL上加上Math.random()，通过不同参数的URL地址响应，否则访问同一个URL资源将不更新。
$('#verification').click(function () { $('#verification').attr('src', 'ImageCodeMakerServlet?' + Math.random()); });
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