问题 在《JSP网络编程从基础到实践》(第二版)的  第23章　学生成绩管理系统　

我在电脑上恢复数据库（已经添加SP4补丁）修改dbconn.java文件后，运行出现错误，
请问具体的操作步骤是什么？或者是我dbconn.java修改错误。

 

出错提示如下：
HTTP 500

org.apache.jasper.JasperException
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:460)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:373)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:329)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)

java.lang.NullPointerException
org.apache.jsp.checkLogin_jsp._jspService(checkLogin_jsp.java:62)
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:331)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:329)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)



The full stack trace of the root cause is available in the Apache Tomcat/5.5.25 logs.