jsp登陆页面和前后台验证并连接数据库

前台login.html和后台verifylogin.jsp两个页面组成:
login.html内容:

verifylogin.jsp内容:
<%@ page language="java" contentType="text/html;charset=gb2312"
pageEncoding="UTF-8"%>

<%@ page import="java.sql.*"%>
<%@ page import="java.util.*"%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>登录</title>

</head>

<body>
   <div align=center>
   <%
    //获取用户名
    String sUserName = request.getParameter ( "txtUserName" );
    //获取密码
    String sPasswd = request.getParameter ( "txtPassword" );

    //登记JDBC驱动程序
    Class.forName ( "org.gjt.mm.mysql.Driver" ).newInstance ( );
    //连接参数与Access不同
    String url = "jdbc:mysql://localhost/LearnJSP";
    //建立连接
    Connection connection = DriverManager.getConnection ( url, "root",
      "011124" );
    //SQL语句
    String sql = "select * from userinfo where username='" + sUserName
      + "' and userpwd = '" + sPasswd + "'";

Statement stmt = connection.createStatement ( );
ResultSet rs = stmt.executeQuery ( sql ); //返回查询结果

    //如果记录集非空，表明有匹配的用户名和密码，登陆成功
    if ( rs.next ( ) )
    {
     out.println ( "登录成功！" );
    } else
    //否则登录失败
    {
     out.println ( "用户名不存在或密码错误！" );
    }

    rs.close ( );
    stmt.close ( );
    connection.close ( );
   %>
</body>
</html>

下面为客户端添加代码验证功能:
<html>
<head>
<title>登录</title>

</head>
   <body>

<form method="post" name="frmLogin" action="verifylogin.jsp">
    <h1 align="center">用户登录</h1><br>
    <div align="center">用户名：
       <input type="text" name="txtUserName" value="Your name"
        onfocus="if(this.value=='Your name')this.value='';"><br>密码：
       <input type="password" name="txtPassword" value="Your password"
        onfocus="if(this.value=='Your password')this.value='';"><br>
       <input type="submit" name="Submit"　value="提交" onClick="validateLogin();" >
             
       <input type="reset" name="Reset" value="重置"><br>
    </div>
</form>

     <script language="javaScript">
      function validateLogin()
      {
       var sUserName = document.frmLogin.txtUserName.value;
       var sPassword = document.frmLogin.txtPassword.value;
       if( sUserName=="" )
       {
        alert("请输入用户名！");
        return false;
       }
       if( sPassword=="" )
       {
        alert("请输入密码！");
        return false;
       }
      }
     </script>
   </body>
</html>

为服务器端添加代码验证功能:
<%@ page language="java" contentType="text/html;charset=gb2312"
pageEncoding="UTF-8"%>

<%@ page import="java.sql.*"%>
<%@ page import="java.util.*"%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>登录</title>

</head>
<body>
   <div align=center>
    <%
     //获取用户名
     String sUserName = request.getParameter ( "txtUserName" );
     if ( sUserName == "" || sUserName == null || sUserName.length()>20 )
     {
      try
      {
       response.sendRedirect ( "login.html" );
      } catch ( Exception e )
      {
      }
     }

     //获取密码
     String sPasswd = request.getParameter ( "txtPassword" );
     if ( sPasswd == "" || sPasswd == null || sPasswd.length()>20 )
     {
      try
      {
       response.sendRedirect ( "login.html" );
      } catch ( Exception e )
      {
      }
     }

     //登记JDBC驱动程序
     Class.forName ( "org.gjt.mm.mysql.Driver" ).newInstance ( );
     //连接参数与Access不同
     String url = "jdbc:mysql://localhost/LearnJSP";
     //建立连接
     Connection connection = DriverManager.getConnection ( url, "root",
       "011124" );
     //SQL语句
     String sql = "select * from userinfo where username='" + sUserName
       + "' and userpwd = '" + sPasswd + "'";

Statement stmt = connection.createStatement ( );
ResultSet rs = stmt.executeQuery ( sql ); //返回查询结果

     //如果记录集非空，表明有匹配的用户名和密码，登陆成功
     if ( rs.next ( ) )
     {
      //登录成功后将sUserName设置为session变量的UserName
      //这样在后面就可以通过 session.getAttribute("UserName") 来获取用户名，
      //同时这样还可以作为用户登录与否的判断依据
      session.setAttribute ( "UserName", sUserName );
      out.print (   "登录成功！" );
      out.print ( session.getAttribute ( "UserName" ) + " 欢迎您！" );
     } else
     //否则登录失败
     {
      out.println ( "用户名不存在或密码错误！" );
     }

     rs.close ( );
     stmt.close ( );
     connection.close ( );
    %>

</body>
</html>

数据库中所有表的字段长度的设计标准是应该是足够用,但不浪费存储空间.
我们可以发现,上面数据库中字段限制在20个字符以内,那么程序中也应该作一个限制,
否则可能给网站出现严重的问题.
将上面源码修改如下:
     .....
     <input type="text" name="txtUserName" value="Your name"
        size="20" maxlength="20"
        onfocus="if(this.value=='Your name')this.value='';"><br>密码：
       <input type="password" name="txtPassword" value="Your password"
        size="20" maxlength="20"
        onfocus="if(this.value=='Your password')this.value='';"><br>
     .....

     .....
     if ( sUserName == "" || sUserName == null || sUserName.length()>20 )
     ....
     if ( sPasswd == "" || sPasswd == null || sPasswd.length()>20 )
     ......

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jsp登陆页面和前后台验证并连接数据库

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