這段時間一直在忙著搞課設，沒顧得上寫，今天終于找到了一點時間，趕快開寫啦~

ImageServlet.java（image.do）：用于生成驗證碼圖片

package com.ymw.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.ServletOutputStream; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import javax.servlet.http.HttpSession;public class ImageServlet extends HttpServlet {private static final long serialVersionUID = 1L;public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doPost(request, response);}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {int width = 80;// 驗證碼圖片寬度int height = 26;// 驗證碼圖片高度BufferedImage image = new BufferedImage(width, height,BufferedImage.TYPE_3BYTE_BGR);Graphics g = image.getGraphics();Random random = new Random();// 創建一個隨機類g.setColor(getRandColor(200, 250));// 背景顏色要偏淡g.fillRect(0, 0, width, height);// 畫背景g.setColor(getRandColor(0, 255));// 邊框顏色g.drawRect(0, 0, width - 1, height - 1);// 畫邊框g.setColor(getRandColor(160, 200));// 隨機產生5條干擾線，使圖象中的認證碼不易被其它程序探測到for (int i = 0; i < 8; i++) {int x = random.nextInt(width);int y = random.nextInt(height);int x1 = random.nextInt(width);int y1 = random.nextInt(height);g.drawLine(x, y, x1, y1);}g.setColor(getRandColor(160, 200));// 隨機產生100點，使圖象中的認證碼不易被其它程序探測到for (int i = 0; i < 100; i++) {int x = random.nextInt(width);int y = random.nextInt(height);g.drawLine(x, y, x, y);}Font font = new Font("Times New Roman", Font.ITALIC, 20); // 創建字體，字體的大小應該根據圖片的高度來定。g.setFont(font);// 設置字體int length = 4; // 設置默認生成4個驗證碼String s = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"; // 設置備選驗證碼:包括"a-z"和數字"0-9"String sRand = "";// 用隨機產生的顏色將驗證碼繪制到圖像中。// 生成隨機顏色(因為是做前景，所以偏深)// 調用函數出來的顏色相同，可能是因為種子太接近，所以只能直接生成g.setColor(new Color(20 + random.nextInt(110),20 + random.nextInt(110), 20 + random.nextInt(110)));for (int i = 0; i < length; i++) {String ch = String.valueOf(s.charAt(random.nextInt(s.length())));sRand += ch;g.drawString(ch, 11 * i + 12, (random.nextInt(5) - 2) * i + 20);}// 將生成的字符串存儲在session中（這點很重要！之后驗證時要用到！）HttpSession session = request.getSession();session.setAttribute("checkCode", sRand);g.dispose();// 圖像生效// 禁止圖像緩存response.setHeader("Pragma", "No-cache");response.setHeader("Cache-Control", "no-cache");response.setDateHeader("Expires", 0);response.setContentType("image/jpeg");// 創建二進制的輸出流ServletOutputStream sos = response.getOutputStream();// 將圖像輸出到Servlet輸出流中。ImageIO.write(image, "jpeg", sos);sos.flush();sos.close();}public Color getRandColor(int lower, int upper) {Random random = new Random();if (upper > 255)upper = 255;if (upper < 1)upper = 1;if (lower < 1)lower = 1;if (lower > 255)lower = 255;int r = lower + random.nextInt(upper - lower);int g = lower + random.nextInt(upper - lower);int b = lower + random.nextInt(upper - lower);return new Color(r, g, b);} }

login.jsp：使用到驗證碼的頁面（該頁面要提交給Login.do—LoginServlet.java）

<script>function changeImage(){var obj = document.getElementById("image");obj.src = "image.do?r="+Math.random();} </script>。。。<tr><td class="field">驗證碼：</td><td><input type="text" name="veryCode" /><img id="image" src="image.do" /><a onclick="changeImage()" style="cursor:pointer">看不清楚？點擊這里更換</a><br />${imageCodeResult }</td> </tr>

style=”cursor:pointer”鼠標移上是手型；

LoginServlet.java：用于處理login.jsp提交上來的請求

public class LoginServlet extends HttpServlet {private static final long serialVersionUID = 1L;public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doPost(request, response);}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {request.setCharacterEncoding("utf-8");//解決亂碼問題String veryCode = request.getParameter("veryCode");//得到用戶輸入的驗證碼//先將從session中獲取的驗證碼與用戶輸入的驗證碼進行比較，如果相同再驗證用戶名和密碼，否則將錯誤信息帶回登陸界面if(veryCode.equals(session.getAttribute("checkCode"))){//進行其他信息的驗證}else {String imageCodeResult="驗證碼輸入錯誤，請重新輸入！";//千萬不要忘記把表示驗證情況的信息放到request中去，否則前臺是不能看到的request.setAttribute("imageCodeResult", imageCodeResult);request.getRequestDispatcher("login.jsp").forward(request, response);}} }

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