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

这是我今天遇到的一个最棘手的问题，耗费了一下午的时间终于解决了。不知道为什么，今天做这个web项目时突然遇到下面这样一个错误：

type Exception report
message
description The server encountered an internal error () that prevented it from fulfilling this request.
exception
org.apache.jasper.JasperException: java.lang.NullPointerException
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:536)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:368)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
cn.jilin.eletric.filter.EncodingFilter.doFilter(EncodingFilter.java:28)
cn.jilin.eletric.filter.LoginFilter.doFilter(LoginFilter.java:39)
root cause
java.lang.NullPointerException
org.apache.jsp.admin.login_jsp._jspInit(login_jsp.java:22)
org.apache.jasper.runtime.HttpJspBase.init(HttpJspBase.java:52)
org.apache.jasper.servlet.JspServletWrapper.getServlet(JspServletWrapper.java:164)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:338)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
cn.jilin.eletric.filter.EncodingFilter.doFilter(EncodingFilter.java:28)
cn.jilin.eletric.filter.LoginFilter.doFilter(LoginFilter.java:39)
note The full stack trace of the root cause is available in the Apache Tomcat/6.0.32 logs.

我百度了很长时间，也没发现解决这类问题的具体方法。其实这个问题不难解决：就是 jar文件 的问题，但是要具体问题具体分析。具体是什么问题要看root cause部分，比如我这里显示的错误如下：

root cause
java.lang.NullPointerException
org.apache.jsp.admin.login_jsp._jspInit(login_jsp.java:22)
org.apache.jasper.runtime.HttpJspBase.init(HttpJspBase.java:52)
org.apache.jasper.servlet.JspServletWrapper.getServlet(JspServletWrapper.java:164)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:338)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
cn.jilin.eletric.filter.EncodingFilter.doFilter(EncodingFilter.java:28)
cn.jilin.eletric.filter.LoginFilter.doFilter(LoginFilter.java:39)

说明我的项目里缺少jsp-api.jar文件我只需要在项目中加上这个文件即可。而有的项目显示数据库连接问题，一般是缺少数据库连接驱动，同样，加上相应的jar文件即可。注意：只是将jar文件放在web-infor下的lib包下是不够的。jar文件的添加方式是：在项目上右键->Build Path->Configer Build Path->Libraries 添加相应的jar文件即可。