请问为什么不能部署运行啊？？
有TreeWiewDemo.war文件 放到webapps文件夹下 运行tomcat 可以自动解压缩 且可以生成CLASS文件，
使用：http://localhost:8080/TreeWiewDemo/dynamicTree.jsp 出现错误如下：

HTTP Status 500 -

--------------------------------------------

type Exception report

message

description The server encountered an internal error () that prevented it from fulfilling this request.

exception

org.apache.jasper.JasperException
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:372)
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)


root cause

java.lang.NullPointerException
book.treeview.Category.FromDb(Category.java:43)
book.treeview.Category. <init> (Category.java:17)
org.apache.jsp.dynamicTree_jsp._jspService(dynamicTree_jsp.java:60)
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)


note The full stack trace of the root cause is available in the Apache Tomcat/5.0.28 logs.


这个是为什么

注：运行tomcat界面正常 运行自己写的HELLOWORD的JSP程序正常

本部署文件为征服AJAX那本书中第十四章的示例


谢谢


[解决办法]
book.treeview.Category.FromDb(Category.java:43)
java.lang.NullPointerException

看这一句啊，空指针。
[解决办法]
找到这个代码看看就知道了
我的异常网推荐解决方案：The server encountered an internal error () that prevented it from fulfilling this request.,http://www.myexception.cn/java-web/317.html