JAVA web数据库登录界面

package com.jaovo.msg.dao;

import java.util.List;

import com.jaovo.msg.model.User;

public interface IUserDao {
    public void add(User user);
    public void delete(int id);
    public void update(User user);
    public User load(int id);
    public User load(String username);
    public List<User> load();
    
}

package com.jaovo.msg.dao;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

import com.jaovo.msg.Util.DBUtil;
import com.jaovo.msg.Util.UserException;
import com.jaovo.msg.model.User;

//import sun.net.www.content.text.plain;

public class UserDaoImpl implements IUserDao {

    @Override
    public void add(User user) {
    
        //获得链接对象
        Connection connection = DBUtil.getConnection();
        //准备sql语句
        String sql = "select count(*) from t_user where username = ?";
        //创建语句传输对象
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        try {
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setString(1, user.getUsername());
            //接收结果集
            resultSet = preparedStatement.executeQuery();
            //遍历结果集
            while(resultSet.next()) {
                if (resultSet.getInt(1) > 0) {
                    throw new UserException("用户已存在") ;
                }
            }
            
            sql = "insert into t_user(username,password,nickname) value (?,?,?)";
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setString(1, user.getUsername());
            preparedStatement.setString(2, user.getPassword());
            preparedStatement.setString(3, user.getNickname());
            preparedStatement.executeUpdate();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally {
            //关闭资源
            DBUtil.close(resultSet);
            DBUtil.close(preparedStatement);
            DBUtil.close(connection);
        }
        
    }

    @Override
    public void delete(int id) {
        Connection connection = DBUtil.getConnection();
        String sql = "delete from t_user where id = ?";
        PreparedStatement preparedStatement = null;
        
        try {
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setInt(1, id);
            preparedStatement.executeUpdate();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally {
            DBUtil.close(preparedStatement);
            DBUtil.close(connection);
        }
        
    }

    @Override
    public void update(User user) {
        Connection connection = DBUtil.getConnection();
        //准备sql语句
        String sql = "update t_user set password = ? , nickname=? where id = ?";
        //创建语句传输对象
        PreparedStatement preparedStatement = null;
        try {
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setString(1, user.getPassword());
            preparedStatement.setString(2, user.getNickname());
            preparedStatement.setInt(3, user.getId());
            preparedStatement.executeUpdate();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally {
            DBUtil.close(preparedStatement);
            DBUtil.close(connection);
        }
    }

    @Override
    public User load(int id) {
        Connection connection = DBUtil.getConnection();
        //准备sql语句
        String sql = "select * from t_user  where id = ?";
        //创建语句传输对象
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        User user = null;
        try {
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setInt(1, id);
            resultSet = preparedStatement.executeQuery();
            while(resultSet.next()) {
                user = new User();
                user.setId(id);
                user.setUsername(resultSet.getString("username"));
                user.setPassword(resultSet.getString("password"));
                user.setNickname(resultSet.getString("nickname"));
            }
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally {
            DBUtil.close(resultSet);
            DBUtil.close(preparedStatement);
            DBUtil.close(connection);
        }
        return  user;
    }

    @Override
    public User load(String username) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public List<User> load() {
        Connection connection = DBUtil.getConnection();
        //准备sql语句
        String sql = "select * from t_user ";
        //创建语句传输对象
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        //集合中只能放入user对象
        List<User> users = new ArrayList<User>();
        User user = null;
        try {
            preparedStatement = connection.prepareStatement(sql);
            resultSet = preparedStatement.executeQuery();
            while(resultSet.next()) {
                user = new User();
                user.setId(resultSet.getInt("id"));
                user.setUsername(resultSet.getString("username"));
                user.setPassword(resultSet.getString("password"));
                user.setNickname(resultSet.getString("nickname"));
                users.add(user);
            }
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally {
            DBUtil.close(resultSet);
            DBUtil.close(preparedStatement);
            DBUtil.close(connection);
        }
        return  users;
    }

}

package com.jaovo.msg.model;

public class User {
    
    private int id;
    private String  username;
    private String  nickname;
    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 getNickname() {
        return nickname;
    }
    public void setNickname(String nickname) {
        this.nickname = nickname;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    
}

package com.jaovo.msg.Util;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class DBUtil {
    
    public  static  Connection getConnection() {
        try {
            //1 加载驱动
            Class.forName("com.mysql.jdbc.Driver").newInstance();
        } catch (InstantiationException | IllegalAccessException | ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        String user = "root";
        String password = "root";
        String url = "jdbc:mysql://localhost:3306/jaovo_msg";
        Connection connection = null;
        try {
            //2 创建链接对象connection
             connection = DriverManager.getConnection(url,user,password);
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return connection;
    }
    
    //关闭资源的方法
    public static void close(Connection connection ) {
        try {
            if (connection != null) {
                connection.close();
            }
            
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    public static void close(PreparedStatement preparedStatement ) {
        try {
            if (preparedStatement != null) {
                preparedStatement.close();
            }
            
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    public static void close(ResultSet resultSet ) {
        try {
            if (resultSet != null) {
                resultSet.close();
            }
            
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    
}

package com.jaovo.msg.Util;

public class UserException extends RuntimeException{

    public UserException() {
        super();
        // TODO Auto-generated constructor stub
    }

    public UserException(String message, Throwable cause, boolean enableSuppression, boolean writableStackTrace) {
        super(message, cause, enableSuppression, writableStackTrace);
        // TODO Auto-generated constructor stub
    }

    public UserException(String message, Throwable cause) {
        super(message, cause);
        // TODO Auto-generated constructor stub
    }

    public UserException(String message) {
        super(message);
        // TODO Auto-generated constructor stub
    }

    public UserException(Throwable cause) {
        super(cause);
        // TODO Auto-generated constructor stub
    }
    
}

<%@page import="com.jaovo.msg.Util.UserException"%>
<%@page import="com.jaovo.msg.dao.UserDaoImpl"%>
<%@page import="com.jaovo.msg.model.User"%>
<%@ 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>
<%
    //接收客户端传递过来的参数
    String username = request.getParameter("username");
    String password = request.getParameter("password");
    String nickname = request.getParameter("nickname");
    if(username == null || "".equals(username.trim())){
        request.setAttribute("error", "用户名不能为空");
    
%>
    <jsp:forward page="addInput.jsp"></jsp:forward>
<%
    }
    User user = new User();
    user.setUsername(username);
    user.setPassword(password);
    user.setNickname(nickname);
    UserDaoImpl userDao = new UserDaoImpl();
    try{
        
    userDao.add(user);
    //重定向
    response.sendRedirect("list.jsp");
%>

    
    
<%
    }catch(UserException e){
%>
    <h2 style="color:red ; font-size:50px">发生错误 : <%=e.getMessage() %></h2>
    <%
    }
    %>
</html>

<%@ 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>用户添加页面</title>
</head>
<body>
    <%=request.getAttribute("error") %>
    <form action="add.jsp" method="get">
        <table align="center" border="1" width="500">
            <tr>
                <td>用户名称 : </td>
                <td>
                    <input type="text" name="username" />
                </td>
            </tr>
                <tr>
                <td>用户密码:</td>
                <td>
                    <input type="password" name="password" />
                </td>
            </tr>
            <tr>
                <td>用户昵称:</td>
                <td>
                    <input type="text" name="nickname" />
                </td>
            </tr>
            <tr align="center">
                <td colspan="2">
                    <input type="submit" value="提交" />
                    <input type="reset" value="重置" />
                </td>
            </tr>
        </table>
    </form>
</body>
</html>

实验结果截图：

错误原因分析：

对数据库练结合使用不熟练，不会对网页进行编写，从零开始有点难，需要付出时间和精力去熟练