实现步骤

1. 创建登录页面表单
2. 配置欢迎页面

web.xml配置示例

<welcome-file-list>
    <welcome-file>login.jsp</welcome-file>
</welcome-file-list>

DAO层实现

用户接口定义

public interface UserRepository {
    User fetchLoginUser(Connection conn, String username) throws SQLException;
}

DAO实现类

public class UserDaoImpl implements UserRepository {
    public User fetchLoginUser(Connection conn, String username) throws SQLException {
        PreparedStatement stmt = null;
        ResultSet result = null;
        User account = null;
        
        if (conn != null) {
            String query = "SELECT * FROM users WHERE username=?";
            Object[] values = {username};
            
            result = DBUtil.executeQuery(conn, stmt, result, query, values);
            if (result.next()) {
                account = new User();
                account.setId(result.getInt("id"));
                account.setUsername(result.getString("username"));
                account.setPassword(result.getString("password"));
                // 其他属性设置
            }
            DBUtil.closeResources(null, stmt, result);
        }
        return account;
    }
}

业务逻辑层

服务接口

public interface AuthService {
    User authenticate(String username, String pwd);
}

服务实现

public class AuthServiceImpl implements AuthService {
    private UserRepository userRepo;
    
    public AuthServiceImpl() {
        userRepo = new UserDaoImpl();
    }
    
    public User authenticate(String username, String pwd) {
        Connection conn = null;
        User account = null;
        try {
            conn = DBUtil.getConnection();
            account = userRepo.fetchLoginUser(conn, username);
        } finally {
            DBUtil.closeConnection(conn);
        }
        return account;
    }
}

控制器实现

public class LoginController extends HttpServlet {
    protected void doPost(HttpServletRequest req, HttpServletResponse res) 
        throws ServletException, IOException {
        
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        
        AuthService auth = new AuthServiceImpl();
        User currentUser = auth.authenticate(username, password);
        
        if (currentUser != null) {
            req.getSession().setAttribute("CURRENT_USER", currentUser);
            res.sendRedirect("home.jsp");
        } else {
            req.setAttribute("ERROR_MSG", "认证失败");
            req.getRequestDispatcher("login.jsp").forward(req, res);
        }
    }
}

组件注册

<servlet>
    <servlet-name>LoginController</servlet-name>
    <servlet-class>com.example.LoginController</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>LoginController</servlet-name>
    <url-pattern>/login</url-pattern>
</servlet-mapping>

安全增强

会话过滤器

public class AuthFilter implements Filter {
    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) 
        throws IOException, ServletException {
        
        HttpServletRequest request = (HttpServletRequest) req;
        User user = (User) request.getSession().getAttribute("CURRENT_USER");
        
        if (user == null) {
            ((HttpServletResponse) res).sendRedirect("/login.jsp");
        } else {
            chain.doFilter(req, res);
        }
    }
}

过滤器配置

<filter>
    <filter-name>AuthFilter</filter-name>
    <filter-class>com.example.AuthFilter</filter-class>
</filter>
<filter-mapping>
    <filter-name>AuthFilter</filter-name>
    <url-pattern>/secure/*</url-pattern>
</filter-mapping>