前提：所使用的页面包括登录页面（login.jsp）、登录成功的页面（index.jsp）、验证码（VerifyCode.java）、登录的Servlet（LoginServlet）、处理验证码的Servlet（VerifyCodeServlet）
整个实现工程的目录结构
1. login.jsp
1 <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
2 <%
3 String path = request.getContextPath();
4 String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
5 %>
6 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
7 <html>
8 <head>
9 <base href="<%=basePath%>">
10 <title>登录页面</title>
11 <meta http-equiv="pragma" content="no-cache">
12 <meta http-equiv="cache-control" content="no-cache">
13 <meta http-equiv="expires" content="0">
14 <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
15 <meta http-equiv="description" content="This is my page">
16 <!--
17 <link rel="stylesheet" type="text/css" href="styles.css">
18 -->
20 </head>
22 <body>
23 <!-- 登录页面 -->
24 <%
25 //获得错误信息
26 String msg="";
27 String msgs=(String)session.getAttribute("msg");
28 if(msgs!=null){
29 msg=msgs; 30 } 31 %> 32 <form action="/review_javaee09/servlet/LoginServlet" method="post"> 33 <table> 34 <caption>用户登录</caption> 35 <tr> 36 <td>用户名：</td> 37 <td><input type="text" name="username" value=""></td> 38 </tr> 39 <tr> 40 <td>密码</td> 41 <td><input type="password" name="pwd" ></td> 42 </tr> 43 <tr> 44 <td>验证码</td> 45 <td><input type="text" name="verify" size=5><a href="javascript:_change()"><img alt="验证码" src="/review_javaee09/servlet/VerifyCodeServlet" id=image></a></td> 46 </tr> 47 <tr> 48 <td><input type="reset" value="重置"></td> 49 <td><input type="submit" value="登录" ></td> 50 </tr> 51 </table> 52 <p> 53 <font size=3 color="red"><%=msg %></font> 54 </p> 55 </form> 56 </body> 57 <script type="text/javascript"> 58 /* 59 实现验证码图片看不清换一张 60 */ 61 function _change(){ 62 document.getElementById("image").src="/review_javaee09/servlet/VerifyCodeServlet?"+new Date().getTime(); 63 } 64 /* 65 此处src必须带有一个可以变化的参数，原因主要是由于当前浏览器的缓存机制 66 */ 67 </script> 68 </html>
2. index.jsp
1 <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
2 <%
3 String path = request.getContextPath();
4 String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
5 %>
6 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
7 <html>
8 <head>
9 <base href="<%=basePath%>">
10 <title>登录成功页面</title>
11 <meta http-equiv="pragma" content="no-cache">
12 <meta http-equiv="cache-control" content="no-cache">
13 <meta http-equiv="expires" content="0">
14 <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
15 <meta http-equiv="description" content="This is my page">
16 </head>
17 <body>
18 <!-- 如果没有登录，跳转到登录页面 -->
19 <%
20 String name=(String)session.getAttribute("username");
21 if(name==null){
22 response.sendRedirect("/review_javaee09/login.jsp");
23 } 24 %> 25 <h1>首页</h1> 26 <p> 27 <font size="5" color="yellow">欢迎<%=name %></font> 28 </p> 29 </body> 30 </html>
3.LoginServlet.java
1 package com.review_javaee09.web.servlet;
2
3 import java.io.IOException;
4 import javax.servlet.ServletException;
5 import javax.servlet.http.Cookie;
6 import javax.servlet.http.HttpServlet;
7 import javax.servlet.http.HttpServletRequest; 8 import javax.servlet.http.HttpServletResponse; 9 import javax.servlet.http.HttpSession; 10 11 import org.apache.jasper.tagplugins.jstl.core.Out; 12 13 14 @SuppressWarnings("serial") 15 public class LoginServlet extends HttpServlet { 16 17 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 18 doPost(request, response); 19 } 20 21 22 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 23 request.setCharacterEncoding("utf-8"); 24 response.setContentType("text/html;charset=utf-8"); 25 26 HttpSession session = request.getSession(); 27 28 String name=request.getParameter("username"); //获得用户名 29 String pwd=request.getParameter("pwd"); //获得密码 30 String verify=request.getParameter("verify"); //获得输入的验证码 31 String verifys = (String) session.getAttribute("verify"); //获得存在session中的验证码 32 if("admin".equals(name)&&"admin".equals(pwd)){//如果用户名和密码正确 33 if(verify.equals(verifys)){//如果验证码正确 34 session.setAttribute("username", name); 35 session.setAttribute("pwd", pwd); 36 request.getRequestDispatcher("/index.jsp").forward(request, response); 37 }else{ //如果验证码不正确 38 String msg="验证码不正确！"; 39 session.setAttribute("msg", msg); 40 request.getRequestDispatcher("/login.jsp").forward(request, response); 41 return; 42 } 43 }else if(name==null||pwd==null||"".equals(name)||"".equals(pwd)){//如果输入的用户名或密码为空 44 String msg="用户名或密码不能为空！"; 45 session.setAttribute("msg", msg); 46 request.getRequestDispatcher("/login.jsp").forward(request, response); 47 return; 48 }else{//其他情况 49 String msg="您输入的用户名或密码不正确，请重新输入！"; 50 session.setAttribute("msg", msg); 51 request.getRequestDispatcher("/login.jsp").forward(request, response); 52 return; 53 } 54 } 55 56 }
4. VerifyCodeServlet
1 package com.review_javaee09.web.servlet;
2
3 import java.awt.image.BufferedImage;
4 import java.io.IOException;
5
6 import javax.servlet.ServletException;
7 import javax.servlet.http.HttpServlet;
8 import javax.servlet.http.HttpServletRequest; 9 import javax.servlet.http.HttpServletResponse; 10 import javax.servlet.http.HttpSession; 11 12 import com.cheryl.commons.VerifyCode; 13 14 15 public class VerifyCodeServlet extends HttpServlet { 16 17 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 18 doPost(request,response); 19 } 20 21 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 22 request.setCharacterEncoding("utf-8"); 23 response.setContentType("text/html;charset=utf-8"); 24 25 VerifyCode vc=new VerifyCode(); //得到验证码对象 26 BufferedImage image = vc.getImage(); //得到验证码图片 27 String text = vc.getText(); //得到验证码的文本 28 HttpSession session = request.getSession(); //将验证码存放到session中 29 session.setAttribute("verify", text); 30 VerifyCode.output(image, response.getOutputStream()); //将验证码图片输出到页面 31 32 } 33 34 }
5. VerifyCode.java（验证码不用自己写，网上有很多源码可以拿来使用，当然也可以自己写）
1 package com.cheryl.commons;
2
3 import java.awt.BasicStroke;
4 import java.awt.Color;
5 import java.awt.Font;
6 import java.awt.Graphics2D;
7 import java.awt.image.BufferedImage; 8 import java.io.IOException; 9 import java.io.OutputStream; 10 import java.util.Random; 11 12 import javax.imageio.ImageIO; 13 14 public class VerifyCode { 15 private int w = 70;//设置缓冲区的宽 16 private int h = 35;//设置缓冲区的宽 17 private Random r = new Random(); 18 //// {"宋体", "华文楷体", "黑体", "华文新魏", "华文隶书", "微软雅黑", "楷体_GB2312"} 19 private String[] fontNames = {"宋体", "华文楷体", "黑体", "华文新魏", "华文隶书", "微软雅黑", "楷体_GB2312"}; 20 //源 21 private String codes = "23456789abcdefghjkmnpqrstuvwxyzABCDEFGHJKMNPQRSTUVWXYZ"; 22 // 背景颜色 23 private Color bgColor = new Color(255, 255, 255); 24 // 保存随机生成的图片当中的内容。 25 private String text ; 26 27 // 随机生成颜色 28 private Color randomColor () { 29 int red = r.nextInt(150); 30 int green = r.nextInt(150); 31 int blue = r.nextInt(150); 32 return new Color(red, green, blue); 33 } 34 35 // 随机生成字体 36 private Font randomFont () { 37 int index = r.nextInt(fontNames.length); 38 String fontName = fontNames[index];//根据随机的索引，获取随机字体 39 int style = r.nextInt(4);//0,1,2,3, 0：没有任何样式，1,加粗，2，斜体，3，加粗和斜体 PLAIN（0）、BOLD(1)、ITALIC(2) 或 BOLD+ITALIC(3)。 40 int size = r.nextInt(5) + 24; //随机生成字号 41 return new Font(fontName, style, size); 42 } 43 44 // 画干扰线 45 private void drawLine (BufferedImage image) { 46 int num = 3;//花三条干扰线 47 Graphics2D g2 = (Graphics2D)image.getGraphics(); 48 for(int i = 0; i < num; i++) { 49 int x1 = r.nextInt(w); 50 int y1 = r.nextInt(h); 51 int x2 = r.nextInt(w); 52 int y2 = r.nextInt(h); 53 g2.setStroke(new BasicStroke(1.5F)); 54 g2.setColor(Color.BLUE); //给干扰线设置了颜色 55 g2.drawLine(x1, y1, x2, y2);//划线 56 } 57 } 58 59 //随机生成字符 60 private char randomChar () { 61 int index = r.nextInt(codes.length()); 62 return codes.charAt(index); 63 } 64 65 // 得到一个缓冲区 66 private BufferedImage createImage () { 67 // 获取一个缓冲区 68 BufferedImage image = new BufferedImage(w, h, BufferedImage.TYPE_INT_RGB); 69 // 得到一个画笔 70 Graphics2D g2 = (Graphics2D)image.getGraphics(); 71 // 设置画笔的颜色 白颜色 72 g2.setColor(this.bgColor); 73 // 填充图片的缓冲区。 74 g2.fillRect(0, 0, w, h); 75 // 将缓冲区返回。 76 return image; 77 } 78 79 // 调用该方法，可以得到验证码 80 public BufferedImage getImage () { 81 BufferedImage image = createImage();//创建图片的缓冲区 82 Graphics2D g2 = (Graphics2D)image.getGraphics();//得到绘制环境(画笔) 83 StringBuilder sb = new StringBuilder();//定义一个容器，用来装在生成的验证码 84 //向图片当中画四个字符 85 for(int i = 0; i < 4; i++) {//循环四次，每次生成一个字符 86 String s = randomChar() + "";//随机成成一个字符 87 sb.append(s); //将生成的字符放在缓冲区 88 float x = i * 1.0F * w / 4; //设置当前字符的x轴坐标 89 g2.setFont(randomFont()); //设置随机生成的字体 90 g2.setColor(randomColor()); //设置字符的随机颜色 91 g2.drawString(s, x, h-5); //画图 92 } 93 this.text = sb.toString(); //随机生成的图片的内容复制给this.text 94 drawLine(image); //画干扰线 95 return image; 96 } 97 98 // 获取图片当中的内容 99 public String getText() { 100 return text; 101 } 102 103 // 保存图片到指定的输出流 104 public static void output (BufferedImage image, OutputStream out) 105 throws IOException { 106 ImageIO.write(image, "JPEG", out); 107 } 108 109 }