javax.servlet.ServletException: Servlet execution threw an exception是什么错误啊？

在运行tomcat时出现以下信息，不知道是什么意思

HTTP Status 500 -

type Exception report

message

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

exception

javax.servlet.ServletException: Servlet execution threw an exception

root cause

java.lang.NoClassDefFoundError: org/apache/commons/dbutils/QueryRunner
com.v512.guestbook.AddMessageServlet.doPost(AddMessageServlet.java:60)
javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
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.

Apache Tomcat/5.0.28

我了个DbUtils组件，它的jar包也放到了WEB-IF/lib目录下了

你使用了dbUtil这个apache的类库，但是没有把它放在运行环境。

NoClassDefFoundError表明，你的编译打包是有此jar包的。