Tomcat7出现HTTP Status 500 - java.lang.ClassCastException: org.apache.jasper.el.ELContextImpl cannot b

好久不碰Java了，心血来潮，决定重新学习，突然发现tomcat已经都运行不了了，还出现了这个问题。问题解决了，不明白问什么，先做记录。

今天在Tomcat7上发布了一个war，过一阵子发现localhost:8080都进不去了。在浏览器输入http://localhost:8080出现如下内容：

HTTP Status 500 - java.lang.ClassCastException: org.apache.jasper.el.ELContextImpl cannot be cast to org.apache.jasper.el.ELContextImpl

type Exception report

message java.lang.ClassCastException: org.apache.jasper.el.ELContextImpl cannot be cast to org.apache.jasper.el.ELContextImpl

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

exception

org.apache.jasper.JasperException: java.lang.ClassCastException: org.apache.jasper.el.ELContextImpl cannot be cast to org.apache.jasper.el.ELContextImpl
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:549)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:470)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
javax.servlet.http.HttpServlet.service(HttpServlet.java:728)

root cause

java.lang.ClassCastException: org.apache.jasper.el.ELContextImpl cannot be cast to org.apache.jasper.el.ELContextImpl
org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate(PageContextImpl.java:1023)
org.apache.jsp.index_jsp._jspService(index_jsp.java:85)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
javax.servlet.http.HttpServlet.service(HttpServlet.java:728)

note The full stack trace of the root cause is available in the Apache Tomcat/7.0.42 logs.

心想真是奇怪了，怎么会有这种问题，于是到网上搜索了以下，看到
http://zhidao.baidu.com/link?url=kF070F2GBut8OmfLq3-LVcCFUM1-qJFcTtz2xIkZ1ekshGRDx64s4hUoiRwyA29TXYwubap9pv4CoF97kP-bpK
里面说是EL表达式的错误，提供了两个解决方案,觉得第二个比较好使，于是修改C:\Tomcat7\conf\context.xml如下：

<?xml version='1.0' encoding='utf-8'?>

<!--

Licensed to the Apache Software Foundation (ASF) under one or more

contributor license agreements. See the NOTICE file distributed with

this work for additional information regarding copyright ownership.

The ASF licenses this file to You under the Apache License, Version 2.0

(the "License"); you may not use this file except in compliance with

the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software

distributed under the License is distributed on an "AS IS" BASIS,

WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

See the License for the specific language governing permissions and

limitations under the License.

-->

<!-- The contents of this file will be loaded for each web application -->

<Context>

<Loader delegate="true" />

<!-- Default set of monitored resources -->

<WatchedResource>WEB-INF/web.xml</WatchedResource>

<!-- Uncomment this to disable session persistence across Tomcat restarts -->

<!--

<Manager pathname="" />

-->

<!-- Uncomment this to enable Comet connection tacking (provides events

on session expiration as well as webapp lifecycle) -->

<!--

<Valve className="org.apache.catalina.valves.CometConnectionManagerValve" />

-->

</Context>

加入了上面的粗体字后，停止Tomcat7服务，在启动Tomcat7服务，还真好使了。

于是记之。

<End>