单列模式下的数据库连接与Servlet之间页面访问用户登录的小例子

下面是我自己写的一个关于servlet的例子

首先是数据库配置，使用的是静态的单例模式

代码如下：

/ 数据库地址连接
// 使用静态单列模式
public class JdbcUtil {
    private static String driverName;
    private static String url;
    private static String username;
    private static String password;

    private static Properties properties = new Properties();

    private static JdbcUtil jdbcUtil;

    private JdbcUtil() {

    }

    public static JdbcUtil getInstance() {
        if (jdbcUtil == null) {
            jdbcUtil = new JdbcUtil();
        }

        return jdbcUtil;

    }

    public static void main(String[] args) {
        JdbcUtil model = new JdbcUtil();
        
    }

    static {
        try {
            // 调用resource包下的dbconfig.properties文件
            InputStream in = Thread.currentThread().getContextClassLoader().getResourceAsStream("dbconfig.properties");
            properties.load(in);

            driverName = properties.getProperty("driverName");
            url = properties.getProperty("url");
            username = properties.getProperty("username");
            password = properties.getProperty("password");

            // 注册
            Class.forName(driverName);

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public Connection getConnection() {
        Connection connection = null;

        try {
            // 连接
            connection = DriverManager.getConnection(url, username, password);

        } catch (Exception e) {
            e.printStackTrace();
        }
        return connection;
    }

    public void close(Connection connection, Statement stmt, ResultSet rs) {
        // 关闭
        if (rs != null) {
            try {
                rs.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

        if (stmt != null) {
            try {
                stmt.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

        if (connection != null) {
            try {
                connection.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}

创建一个source文件夹命名为resources，在其创建dbconfig.properties文件，里面写的是你数据库的地址、用户和密码

driverName=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/test
username=root
password=1

 接着，创建实体类User

// POJO实体类
public class User {

    // 用户名
    private String username;

    // 密码
    private String password;

    public User() {
        super();
    }

    // get、set方法
    public User(String username, String password) {
        super();
        this.username = username;
        this.password = password;
    }

    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;
    }

    // toString方法
    @Override
    public String toString() {
        return "User [username=" + username + ", password=" + password + "]";
    }

}

创建接口的dao包

// 接口
public interface IUserDao {

    // 增加

    public abstract boolean insertUser(User model);

    // 删除

    public abstract boolean deleteUser(String userName);

    // 修改

    public abstract boolean updateUser(User model);

    // 查询（所有）

    public abstract List<User> findAll();

    // 查询（条件）

    public abstract boolean findByTerm(User model);

}

然后实现接口的方法，里面直接写sql语句

// 接口实现
public class UserDaoImpl implements IUserDao {
    /**
     * 用户增加
     */
    @Override
    public boolean insertUser(User model) {
        boolean flag = false;
        Connection connection = null;
        PreparedStatement pstmt = null;

        try {
            // 连接
            connection = JdbcUtil.getInstance().getConnection();

            // SQL语句
            String sql = " INSERT INTO user (username,`password`) VALUES (?,?)";

            // 创建Statement对象
            pstmt = connection.prepareStatement(sql);
            pstmt.setString(1, model.getUsername());
            pstmt.setString(2, model.getPassword());

            // 执行
            int result = pstmt.executeUpdate();
            System.out.println("受影响的行数" + result);
            flag = true;

        } catch (Exception e) {
            flag = false;
            e.printStackTrace();
        } finally {
            // 关闭
            JdbcUtil.getInstance().close(connection, pstmt, null);
        }

        return flag;
    }

    /**
     * 用户删除
     */
    @Override
    public boolean deleteUser(String userName) {
        boolean flag = false;
        Connection connection = null;
        PreparedStatement pstmt = null;

        try {
            // 连接
            connection = JdbcUtil.getInstance().getConnection();

            // SQL语句
            String sql = "DELETE FROM user WHERE username = ? ";

            // 创建Statement对象
            pstmt = connection.prepareStatement(sql);
            pstmt.setString(1, userName);

            // 执行
            int result = pstmt.executeUpdate();
            System.out.println("受影响的行数" + result);
            flag = true;

        } catch (Exception e) {
            flag = false;
            e.printStackTrace();
        } finally {
            // 关闭
            JdbcUtil.getInstance().close(connection, pstmt, null);
        }

        return flag;
    }

    /**
     * 用户修改
     */
    @Override
    public boolean updateUser(User model) {
        boolean flag = false;
        Connection connection = null;
        PreparedStatement pstmt = null;

        try {
            // 连接
            connection = JdbcUtil.getInstance().getConnection();

            // SQL语句
            String sql = "UPDATE  user SET  `password` = ?  WHERE username = ? ";

            // 创建Statement对象
            pstmt = connection.prepareStatement(sql);
            pstmt.setString(1, model.getPassword());
            pstmt.setString(2, model.getUsername());

            System.err.println(pstmt);

            // 执行
            int result = pstmt.executeUpdate();
            System.out.println("受影响的行数" + result);
            flag = true;
        } catch (Exception e) {
            flag = false;
            e.printStackTrace();
        } finally {
            // 关闭
            JdbcUtil.getInstance().close(connection, pstmt, null);
        }

        return flag;
    }

    /**
     * 用户查询（所有）
     */
    @Override
    public List<User> findAll() {
        List<User> list = new ArrayList<User>();
        Connection connection = null;
        PreparedStatement pstmt = null;
        ResultSet rs = null;

        try {
            // 连接
            connection = JdbcUtil.getInstance().getConnection();

            // SQL语句
            String sql = "SELECT * FROM user";

            // 创建Statement对象
            pstmt = connection.prepareStatement(sql);

            // 执行
            rs = pstmt.executeQuery();
            // 游标向下移动一行
            while (rs.next()) {
                User model = new User();
                model.setUsername(rs.getString("username"));
                model.setPassword(rs.getString("password"));
                // 添加到集合
                list.add(model);
            }

        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JdbcUtil.getInstance().close(connection, pstmt, null);
        }

        return list;
    }

    /**
     * 用户查询（根据条件）
     */
    public boolean findByTerm(User model) {
        boolean flag = false;
        Connection connection = null;
        PreparedStatement pstmt = null;
        ResultSet rs = null;

        try {
            // 连接
            connection = JdbcUtil.getInstance().getConnection();

            // SQL语句
            String sql = "SELECT *  FROM user WHERE username=? AND  `password` = ? ";

            // 创建Statement对象
            pstmt = connection.prepareStatement(sql);
            pstmt.setString(1, model.getUsername());
            pstmt.setString(2, model.getPassword());

            // 执行
            rs = pstmt.executeQuery();

            // 判断数据库是否为空
            if (rs != null && rs.next()) {
                flag = true;
            }

        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            // 关闭
            JdbcUtil.getInstance().close(connection, pstmt, null);
        }

        return flag;
    }

}

最后写servlet

/**
 * Servlet implementation class Login 登录页面
 */
@WebServlet("/Login")
public class LoginServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
     *      response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 在reques请求接收参数之前，先设置请求的字符编码为UTF-8
        request.setCharacterEncoding("UTF-8");
        // 在response响应返回数据时，也要设置
        response.setContentType("text/html; charset=UTF-8");
        response.setCharacterEncoding("UTF-8");

        // 调用实体类
        User model = new User();

        // 获取http提交过来的数据
        model.setUsername(request.getParameter("username"));
        model.setPassword(request.getParameter("password"));

        // 调用接口实现的方法
        IUserDao dao = new UserDaoImpl();

        // 判断是否为空
        if (model.getUsername() == null || model.getPassword() == null) {
            // 转发到登录界面
            request.getRequestDispatcher("jsp/login.jsp").forward(request, response);
        } else {

            // 调用条件查找的方法，判断数据库有无该数据
            if (dao.findByTerm(model)) {
                // 重定向到进入页面
                response.sendRedirect("jsp/index.jsp");
            } else {
                request.setAttribute("msg", "帐户或密码出错！");
                // 还是留在登录界面
                request.getRequestDispatcher("jsp/login.jsp").forward(request, response);
            }
        }

    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
     *      response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);

    }
}

 login.jsp下面的代码

<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title>C9登录界面</title>
<meta charset="UTF-8" />
<link href="css/bootstrap.min.css" rel="stylesheet">
<link href="css/login.css" rel="stylesheet" type="text/css" />
<script src="http://libs.baidu.com/jquery/2.1.4/jquery.min.js"></script>
<script src="js/login.js" type="text/javascript"></script>
<script src="js/image.js" type="text/javascript"></script>
</head>
<body id="main" onload="showBgImage();init();">
    <form action="Login" method="post">
        <div class="login_m">
            <div class="login_logo">
                <h1 style="font-family: '宋体'; font-size: 36px;">C9决策分析门户登录</h1>
            </div>

            <div class="login_boder">
                <div class="login_padding">
                    <div class="form-group">
                        <label for="userName"></label> 
                        <input type="text" class="form-control " id="txtUserName" name="username" placeholder="用户名">
                    </div>

                    <div class="form-group">
                        <label for="passWord"></label> 
                        <input type="password" class="form-control" id="txtPassWord" name="password" placeholder="密码">
                    </div>

                    <div class="rem_sub">
                        <div class="rem_sub_l">
                            <input type="checkbox" name="checkbox" id="chkRemember"> <label for="chkRemember">下次自动登录</label>
                        </div>

                        <div class="join">
                            <input type="submit" id="btnSubmit" name="submit" class="btn btn_block btn_success" value="登录" />
                        </div>
                    </div>
                    
                    <div class="forgot">
                        <a href="jsp/forget.jsp">忘记密码?</a> <span class="split"></span> <a href="jsp/register.jsp">免费注册</a>
                    </div>
                </div>

                <footer class="footer"> <i><a href="http://www.cnbisoft.com">经邦信息技术有限公司</a></i> <br>
                <span>经邦软件&nbsp;2010&nbsp;©2008-2016&nbsp;皖ICP备15018743号</span>
                <div class="time" id="txt"></div>
                </footer>
            </div>
        </div>
    </form>

    <div class="msg">
        <span style="color: red; margin-top: 10px;"> 
<%
     String msg = (String) request.getAttribute("msg");
     if (msg == null) {
         out.println();
     } else {
         out.println(msg);
     }
 %>
        </span>
    </div>
</body>
</html>

访问localhost：8080/项目名/Login，就能看到

注意：上面重定向之后的页面我都没传，这个要自己写jsp

说的不是怎么好，看注释应该可以理解到~~