实现简单的登录界面

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））

程序源代码：

DBUtil.java

package com.jaovo.msg.Util;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
public class DBUtil {
    public static Connection getConnection() {
        try {
            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 {
            connection = DriverManager.getConnection(url, user, password);
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return connection;
    }
}

<%@page import = "com.jaovo.msg.Util.DBUtil" %>
<%@page import = "java.sql.*" %>
<%@page import = "java.sql.PreparedStatement" %>
<%@ 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>
<%
    String username = request.getParameter("username");
    String password = request.getParameter("password");
    if(username == null || "".equals(username.trim())){
        request.setAttribute("result", "请输入用户名!");
%>
        <jsp:forward page = "longinwindow.jsp"></jsp:forward>
<%
    }
    if(password == null || "".equals(password.trim())){
        request.setAttribute("result", "请输入密码!");
%>
        <jsp:forward page = "longinwindow.jsp"></jsp:forward>
<%
    }
    Connection connection = DBUtil.getConnection();
    boolean flag = false;
    String sql = "select * from t_user where username = ?";
    PreparedStatement preparedstatement = null;
    ResultSet resultset = null;
    preparedstatement = connection.prepareStatement(sql);
    preparedstatement.setString(1,username);
    resultset = preparedstatement.executeQuery();
    while(resultset.next()){
            if(resultset.getString("password").equals(password)){
                flag = true;
                request.setAttribute("result", "登陆成功！");
%>
                <%=request.getAttribute("result")%>
<%
            }
            else{
                request.setAttribute("result", "密码错误！请重新登录！");
%>
                <jsp:forward page = "longinwindow.jsp"></jsp:forward>
<%

            }
    }
    if(!flag){
        request.setAttribute("result", "没有这个人！登录失败！");
%>
        <jsp:forward page = "longinwindow.jsp"></jsp:forward>
<%
    }
%>
</html>

loginwindow.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>用户登录页面</title>
</head>
<body>
    <%=request.getAttribute("result") %>
    <form action="login.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 align = "center">
                    <td colspan = "2">
                            <input type = "submit" value = "登录"/>
                            <input type = "reset" value = "重置"/>
                    </td>
            </tr>
        </table>
    </form>
</body>
</html>

运行结果截图：

什么都不输入的情况下：

密码输入错误的情况下：

没有用户的情况下：

登录成功时：