疯了 疯了!!!~~~ 快来救我~~~~~~
exception  

org.apache.jasper.JasperException:   Exception   in   JSP:   /chklogin.jsp:11

8:   String   sql   =   "SELECT   *   FROM   userpassword   WHERE   USER_ID= ' "+userid+ " '   AND   USER_PASSWORD= ' "+password+ " ' ";
9:     DBSQLManager   dbsm   =   new   DBSQLManager();
10:     dbsm.setsqlstr(sql);
11:     dbsm.executequery();
12:   ResultSet   rs   =     dbsm.getrs();
13:   if   (!rs.next())  
14:           {


Stacktrace:
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:467)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:389)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:315)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)


root   cause  

java.lang.NullPointerException
shell.DBSQLManager.executequery(DBSQLManager.java:59)
org.apache.jsp.chklogin_jsp._jspService(chklogin_jsp.java:84)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:98)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:328)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:315)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)


下面是相关的文件.
package   shell;


import   java.sql.*;
import   shell.*;
public   class   DBSQLManager
{
protected   Connection   conn=null;
protected   Statement   stmt=null;
protected   ResultSet   rs=null;
protected   String   sqlstr;

public   DBSQLManager()
{
try
{
sqlstr= " ";

DBConnectionManager   dcm=new   DBConnectionManager();
conn=dcm.getconnection();
stmt=conn.createStatement();


}  
catch   (Exception   e)
{
e.printStackTrace();
}
}

public   Statement   getstmt()
{
return   stmt;
}

public   Connection   getconn()
{
return   conn;
}

public   ResultSet   getrs()
{
return   rs;
}

public   void   setsqlstr(String   newsqlstr)
{
this.sqlstr=newsqlstr;
}

public   String   getsqlstr()
{
return   sqlstr;
}

public   void   executequery()   throws   Exception
{

rs=stmt.executeQuery(sqlstr);


}

public   void   execeteupdate()   throws   Exception
{
stmt.executeUpdate(sqlstr);
}

public   void   close()   throws   关于登记的服务器端判断