Servlet+JDBC实现登陆功能的小例子(带验证码)-Java开发

下面是“Servlet+JDBC实现登陆功能的小例子(带验证码)”的完整攻略，包含以下内容：

下面是“Servlet+JDBC实现登陆功能的小例子(带验证码)”的完整攻略，包含以下内容：

需求分析

我们需要实现一个包含验证码的登陆功能，用户需要输入用户名、密码和验证码，当用户点击提交按钮时，系统会校验用户的输入，如果输入正确，则跳转到登录成功页面，否则提示错误信息。

技术选择

我们使用Servlet技术实现用户输入数据的接收和校验，使用JDBC技术实现数据的存储和查询，使用JSP技术实现登录成功页面的展示。

开发步骤

步骤一：创建数据库和数据表

在MySQL数据库中创建一个名为“test”的数据库，并在该数据库中创建一个名为“user”的数据表，该数据表包含以下字段：

id（int）：主键字段；
username（varchar）：用户名字段；
password（varchar）：密码字段。

步骤二：创建JavaBean类

创建一个JavaBean类User，用于表示用户信息，该类的代码如下：

public class User {
    private int id;
    private String username;
    private String password;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }
}

步骤三：编写DAO层代码

编写一个UserDAO类，用于实现与数据库的数据交互，该类的代码如下：

public class UserDAO {
    private Connection conn = null;
    private PreparedStatement ps = null;
    private ResultSet rs = null;

    // 连接数据库方法
    private void getConn() throws Exception {
        Class.forName("com.mysql.jdbc.Driver");
        String url = "jdbc:mysql://localhost:3306/test";
        String username = "root";
        String password = "root";
        conn = DriverManager.getConnection(url, username, password);
    }

    // 关闭数据库方法
    private void closeConn() throws Exception {
        if (rs != null) {
            rs.close();
        }
        if (ps != null) {
            ps.close();
        }
        if (conn != null) {
            conn.close();
        }
    }

    // 查询用户方法
    public User getUser(String username, String password) throws Exception {
        getConn();
        String sql = "select * from user where username=? and password=?";
        ps = conn.prepareStatement(sql);
        ps.setString(1, username);
        ps.setString(2, password);
        rs = ps.executeQuery();
        User user = null;
        while (rs.next()) {
            user = new User();
            user.setId(rs.getInt("id"));
            user.setUsername(rs.getString("username"));
            user.setPassword(rs.getString("password"));
        }
        closeConn();
        return user;
    }

    // 保存用户方法
    public void saveUser(User user) throws Exception {
        getConn();
        String sql = "insert into user (username,password) values(?,?)";
        ps = conn.prepareStatement(sql);
        ps.setString(1, user.getUsername());
        ps.setString(2, user.getPassword());
        ps.executeUpdate();
        closeConn();
    }
}

步骤四：编写Servlet代码

编写一个LoginServlet类，用于实现用户登录的功能，包括输入数据的接收和校验，验证码的生成和校验，以及页面的跳转等，该类的代码如下：

public class LoginServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    // 生成指定长度的随机字符串
    private String getRandomString(int length) {
        String str = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
        Random random = new Random();
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < length; i++) {
            int number = random.nextInt(62);
            sb.append(str.charAt(number));
        }
        return sb.toString();
    }

    //生成验证码图片
    private void outputCaptcha(HttpServletRequest request, HttpServletResponse response) throws IOException {
        // 设置响应的类型格式为图片格式
        response.setContentType("image/jpeg");
        //禁止图像缓存。
        response.setHeader("Cache-Control", "no-store");
        response.setHeader("Pragma", "no-cache");
        response.setDateHeader("Expires", 0);

        int width = 80, height = 30;
        BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);

        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", Font.PLAIN, 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 captcha = getRandomString(4);
        request.getSession().setAttribute("captcha", captcha);
        g.setFont(new Font("Arial", Font.BOLD, 20));
        g.setColor(new Color(20 + random.nextInt(110), 20 + random.nextInt(110), 20 + random.nextInt(110)));
        g.drawString(captcha, 15, 25);
        g.dispose();

        ImageIO.write(image, "JPEG", response.getOutputStream());
    }

    //获取给定范围内的随机颜色
    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);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setCharacterEncoding("UTF-8");
        response.setCharacterEncoding("UTF-8");
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        String captcha = request.getParameter("captcha");
        String sessionCaptcha = (String) request.getSession().getAttribute("captcha");
        if (captcha == null || !captcha.equals(sessionCaptcha)) {
            request.setAttribute("message", "验证码错误");
            request.getRequestDispatcher("/login.jsp").forward(request, response);
            return;
        }
        UserDAO dao = new UserDAO();
        User user = null;
        try {
            user = dao.getUser(username, password);
        } catch (Exception e) {
            e.printStackTrace();
        }
        if (user == null) {
            request.setAttribute("message", "用户名或密码错误");
            request.getRequestDispatcher("/login.jsp").forward(request, response);
        } else {
            request.getRequestDispatcher("/success.jsp").forward(request, response);
        }
    }
}

步骤五：编写验证码页面代码

编写一个captcha.jsp页面，用于显示验证码图片，该页面的代码如下：

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ page import="java.awt.*,java.awt.image.*"%>

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Captcha</title>
</head>
<body>
    <img src="loginServlet?method=outputCaptcha" onclick="this.src='loginServlet?method=outputCaptcha&' + Math.random();" />
</body>
</html>

步骤六：编写登录页面代码

编写一个login.jsp页面，用于输入用户名、密码和验证码，该页面的代码如下：

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Login</title>
</head>
<body>
    <form action="loginServlet" method="post">
        <label>用户名：</label><input type="text" name="username" /><br />
        <label>密&nbsp;&nbsp;&nbsp;码：</label><input type="password" name="password" /><br />
        <label>验证码：</label><input type="text" name="captcha" /><img src="captcha.jsp" /><br />
        <input type="submit" value="登录" />
    </form>
    <% if (request.getAttribute("message") != null) { %>
        <p><%= request.getAttribute("message") %></p>
    <% } %>
</body>
</html>

步骤七：编写登录成功页面代码

编写一个success.jsp页面，用于显示登录成功的信息，该页面的代码如下：

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Login Success</title>
</head>
<body>
    <h1>Login Success</h1>
    <p>欢迎您，<%= request.getParameter("username") %>！</p>
</body>
</html>