如何实现一个服务器一个session为一个用户服务的/
为什么要验证码？
原理（java的绘图技术）
验证码：
package com.dalao; 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; import javax.servlet.http.HttpSession; /** * Servlet implementation class CodeUtil */ @WebServlet("/codeutil") public class CodeUtil extends HttpServlet { private static final long serialVersionUID = 1L; /** * @see HttpServlet#HttpServlet() */ public CodeUtil() { super(); // TODO Auto-generated constructor stub } /** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse * response) */ protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // System.out.println("哈哈哈"); response.setContentType("image/jpeg"); // 设置页面不缓存 response.setHeader("Pragma", "No-cache"); response.setHeader("Cache-Control", "no-cache"); response.setDateHeader("Expires", 0); // 在内存中创建图像 int width = 90; int height = 35; BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB); // 获取图形上下文 Graphics g = image.getGraphics(); // 随机类 Random random = new Random(); // 设定背景 g.setColor(getRandColor(200, 250)); g.fillRect(0, 0, width, height); // 设定字体 g.setFont(new Font("Times New Roman", Font.PLAIN, 30)); // 随机产生干扰线 g.setColor(getRandColor(160, 200)); for (int i = 0; i < 100; 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); } // 随机产生4位验证码 String[] codes = { "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", "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" }; String code = ""; for (int i = 0; i < 4; i++) { String str = codes[random.nextInt(codes.length)]; code += str; // 将认证码显示到图象中 g.setColor(new Color(50 + random.nextInt(110), 20 + random.nextInt(110), 30 + random.nextInt(110))); // 调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成 g.drawString(str, 18 * i + 13, 27); // 文字间距*i+距离左边距，上边距 } HttpSession session = request.getSession(); // 将认证码存入SESSION session.setAttribute("code", code); // 图象生效 g.dispose(); // 输出图象到页面 ImageIO.write(image, "JPEG", response.getOutputStream()); // 加上下面代码,运行时才不会出现java.lang.IllegalStateException: getOutputStream() has // already been called ..........等异常 response.getOutputStream().flush(); response.getOutputStream().close(); response.flushBuffer(); } // 获取随机颜色 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); } /** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse * response) */ protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } }
登录界面;
package com.dalao; import java.io.IOException; import java.io.PrintWriter; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; /** * Servlet implementation class Loin */ @WebServlet("/Loin") public class LoginServlet extends HttpServlet { private static final long serialVersionUID = 1L; /** * @see HttpServlet#HttpServlet() */ public LoginServlet() { super(); // TODO Auto-generated constructor stub } /** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */ protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub //浏览器uft-8展示 response.setContentType("text/html;charset=utf-8"); request.setCharacterEncoding("utf-8"); PrintWriter out=response.getWriter(); //返回一个界面 // out.println("你好"); out.print("<img src='img/1.gif'/><hr/>"); out.println("<h1>用户登录</h1>"); out.println("<form action='/mycheckCode/LoinCL' method='post'>"); out.println("用户id:<input type='text' name='id'></br>"); out.println("密 码:<input type='password' name='password'></br>"); out.println("验证码:<input type='text' name='checkcode'><img src='/mycheckCode/codeutil'></br>"); out.println("<input type='submit' value='登录'></br>"); out.println("</form>"); String err=(String) request.getAttribute("err"); if(err!=null){ out.print(err); } } /** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */ protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub this.doGet(request,response); } }
登录界面的控制;
package com.dalao; import java.io.IOException; import java.io.PrintWriter; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; /** * Servlet implementation class LoinCL */ @WebServlet("/LoinCL") public class LoinCL extends HttpServlet { private static final long serialVersionUID = 1L; /** * @see HttpServlet#HttpServlet() */ public LoinCL() { super(); // TODO Auto-generated constructor stub } /** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */ protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub response.setContentType("text/html;charset=utf-8"); request.setCharacterEncoding("utf-8"); PrintWriter out=response.getWriter(); //获取用户的ID password 输入的验证码 //1.先验证码 String id=request.getParameter("id"); String password=request.getParameter("password"); String checkcode=request.getParameter("checkcode"); //取出session中验证码 String checkcode2=(String) request.getSession().getAttribute("code"); if(checkcode.equals(checkcode2)){ out.print("验证码正确"); }else{ // out.print("重新输入"); request.setAttribute("err", "验证码错误"); request.getRequestDispatcher("/Loin").forward(request, response); } } /** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */ protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub this.doGet(request, response); } }