00-实现简单的登陆界面

1．需要掌握的技术；

Java语言（Java database Connectivity技术、Servlet技术、jsp(Java Server Pages)技术，JavaBean(Application)应用组件技术）、面向对象分析设计思想、设计模式和框架结构、XML语言、网页脚本语言、开发工具（数据库、web服务器、集成开发环境（IDE））

源代码：

1.DBUtil

package com.jaovo.msg.util;
import java.sql.*;
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();
        }
    }
}

2.add.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
 <%@ page import = "com.jaovo.msg.util.DBUtil" %> 
<%@ page import = "java.sql.*" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<%
    //接受客户端传递过来的参数
    String username = request.getParameter("username");
    if(username==null||"".equals(username))
    {
        request.setAttribute("哎呀", "请输入用户名!");    
        %>
        <jsp:forward page="addInput.jsp"></jsp:forward>
        <% 
    }
    String password = request.getParameter("password");
    String sql="select * from t_user where username=?";
    Connection connection=DBUtil.getConnection();
    PreparedStatement preparedStatement=connection.prepareStatement(sql);
    preparedStatement.setString(1, username);
    ResultSet resultset=preparedStatement.executeQuery();
    boolean flag=false;
    while(resultset.next())
    {
        flag=true;
        if(resultset.getString("password").equals(password))
        {
            request.setAttribute("哎呀", "登陆成功，你是真的厉害!");    
            %>
            
            <%=request.getAttribute("哎呀")%>
            <% 
            
        }
        else
        {
            request.setAttribute("哎呀", "登录失败，你好low!");
            %>
            <jsp:forward page="addInput.jsp"></jsp:forward>
            <% 
        }
    
    }
    if(!flag)
    {
        request.setAttribute("哎呀","用户不存在!");
        
        %>
        <jsp:forward page="addInput.jsp"></jsp:forward>
        <% 
        
    }
    
    
    
%>
<body>
    
</body>
</html>

3.addInput.jsp

<%@ 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>用户登录界面</title>
</head>
<body>
    <form action="add.jsp" method="get">
    <%=request.getAttribute("哎呀") %>
        <table align="center" border="1" width="500">
            <tr>
                <td>用户名：</td>
                <td>
                    <input type="text" name="username"/>
                </td>
            </tr>
            <tr>
                <td>输入密码：</td>
                <td>
                    <input type="password" name="password"/>
                </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>