用户的登录、注册和退出是一个系统最常见的功能，现将各功能用jsp代码表示出来

用户的登录：

其中connDB是数据库连接类，将用户名username放入session中

<%@ page contentType="text/html; charset=gb2312" language="java" import="java.sql.*" errorPage="" %>
<jsp:useBean id="connBean" scope="page" class="beans.connDB"/>
<%
request.setCharacterEncoding("GB2312");
String username=request.getParameter("username");
String PWD=request.getParameter("PWD");
if(username!=""){%>
<%	ResultSet rs=connBean.executeQuery("select * from tb_User where UserName='"+username+"'");
	if (rs.next()){
		String rsPWD=rs.getString("PWD");
		if(PWD.equals(rsPWD)){%>
			<script language="javascript">
			opener.location.reload();
			window.close();
			</script>
		<%
                session.setAttribute("username",username);
		}else{%>
		<script language="javascript">
		alert("您输入的密码不正确，请重新输入！");
		history.back();
		</script>
		<%}
	}else{ %>
<script language="javascript">
alert("您输入的用户名不正确，请重新输入！");
history.back();
</script>
<%}
}%>

用户的注册：

<%@ page contentType="text/html; charset=gb2312" language="java" import="java.sql.*" errorPage="" %>
<jsp:useBean id="connBean" scope="page" class="beans.connDB"/>

<%
request.setCharacterEncoding("GB2312");
String username=request.getParameter("username");
String PWD=request.getParameter("PWD1");
String birthday=request.getParameter("birthday");
String sex=request.getParameter("sex");
String OICQ=request.getParameter("OICQ");
String tel=request.getParameter("tel");
String homepage=request.getParameter("homepage");
String address=request.getParameter("address");
String postcode=request.getParameter("postcode");
String Email=request.getParameter("Email");
ResultSet rs=connBean.executeQuery("select * from tb_user where username='"+username+"'");
if (rs.next()){
	out.println("<script language='javascript'>alert('该用户名已经存在，请重新注册！');window.location.href='reg.jsp';</script>");
}else{
	String sql="Insert into tb_User values('"+username+"','"+PWD+"','"+birthday+"','"+sex+"','"+OICQ+"','"+tel+"','"+homepage+"','"+address+"','"+postcode+"','"+Email+"',default )";
	int ret=0;
	ret=connBean.executeUpdate(sql);
	if (ret!=0){
		out.println("<script language='javascript'>alert('用户注册成功！');window.location.href='index.jsp';</script>");
		}else{
		out.println("<script language='javascript'>alert('用户注册失败！');window.location.href='reg.jsp';</script>");
	}
}
%>

这其中必须注意不能简单的退到登录页面，而要在退出的时候将session中的用户名username清空。

<%@ page contentType="text/html; charset=gb2312" language="java" import="java.sql.*" errorPage="" %>

<%
session.removeAttribute("username");  //清空Session变量
response.sendRedirect("index.jsp");
%>