HTTP Status 500 - 中java.lang.NullPointerException错误，请大家帮忙解决，非常感谢！

程序为
<%@page contentType="text/html; charset=GB18030"%>
<%@page import="javainfo.*"%>
<%@page import="java.sql.*"%>
<jsp:useBean id="bean1" scope="session" class="javainfo.User"/>
<jsp:setProperty name="bean1" property="*"/>
<%Connection conn=null;
//String userNameSelection = request.getParameter("loginSelection");
//String userID=request.getParameter("userID");
//String password=request.getParameter("password");
try{
if((bean1.getLoginSelection()).equalsIgnoreCase("Teacher"))
{
conn=DBConnection.getConnection();
PreparedStatement pStat=conn.prepareStatement("select name,Password from Manager where ID=? and Password=?");
pStat.setString(1,bean1.getUserID());
pStat.setString(2,bean1.getPassword());
ResultSet rs=pStat.executeQuery();
if(rs.next()){
session.setAttribute("session_userBean",bean1);%>
<jsp:forward page="ManagerControl.jsp"></jsp:forward>
<%}else{%>
<jsp:forward page="ErrorUserOrPassword.jsp"></jsp:forward>
<%}}
else if((bean1.getLoginSelection()).equalsIgnoreCase("Student"))
{
conn=DBConnection.getConnection();
PreparedStatement pStat=conn.prepareStatement("select name,password from Student where id=? and password=?");
pStat.setString(1,bean1.getUserID());
pStat.setString(2,bean1.getPassword());
ResultSet rs=pStat.executeQuery();
if(rs.next()){
session.setAttribute("session_userBean",bean1);
%>
<jsp:forward page="StartTest.jsp"></jsp:forward>
<%}else{%>
<jsp:forward page="ErrorUserOrPassword.jsp"></jsp:forward>
<%}}else{
%>
<jsp:forward page="ErrorUserOrPassword.jsp"></jsp:forward>
<%}}finally{
if(conn!=null)conn.close();}
%>

给出错误原因是：
root cause java.lang.NullPointerException
org.apache.jsp.switch_jsp._jspService(switch_jsp.java:68)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:94)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:324)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
数据库连接BEAN为：
import java.sql.*;

public class DBConnection{
public static Connection getConnection()throws SQLException{
try{
Class.forName("com.microsoft.jdbc.sqlserver.SQLServerDriver");
}
catch(ClassNotFoundException ex){
ex.printStackTrace();
return null;
}

return DriverManager.getConnection("jdbc:sqlserver://localhost:1433；DatabaseName=TestSystem","sa","811026");
}

}
这里有错误吗？
经分析查处，是此处
PreparedStatement pStat=conn.prepareStatement("select name,Password from Manager where ID=? and Password=?");
出现错误，但是不知道是什么原因。

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