求助

运行tomcat时出现这个错误提示
HTTP Status 500 - An exception occurred processing JSP page /index.jsp at line 5type Exception reportmessage An exception occurred processing JSP page /index.jsp at line 5description The server encountered an internal error that prevented it from fulfilling this request.exceptionorg.apache.jasper.JasperException: An exception occurred processing JSP page /index.jsp at line 52: <%
3:  String user = (String)session.getAttribute("user");
4:  if(user == null){//涓虹敤鎴风敓鎴愭樀绉
5:  user = "璁垮" + SendMessageServlet.ONLINE_USER_COUNT;
6:  SendMessageServlet.ONLINE_USER_COUNT ++;
7:  session.setAttribute("user", user);
8:  }
Stacktrace:
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:567)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:454)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:396)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:340)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
root causejavax.servlet.ServletException: java.lang.NoSuchFieldError: ISO_8859_1
org.apache.jasper.runtime.PageContextImpl.doHandlePageException(PageContextImpl.java:908)
org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:837)
org.apache.jsp.index_jsp._jspService(index_jsp.java:163)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:431)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:396)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:340)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
root causejava.lang.NoSuchFieldError: ISO_8859_1
org.apache.catalina.websocket.WebSocketServlet.<clinit>(WebSocketServlet.java:49)
org.apache.jsp.index_jsp._jspService(index_jsp.java:96)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:431)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:396)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:340)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
note The full stack trace of the root cause is available in the Apache Tomcat/8.0.21 logs.Apache Tomcat/8.0.21接下来是源码
<%@ page language="java" pageEncoding="UTF-8" import="com.ghj.packageofservlet.SendMessageServlet"%>
<%
String user = (String)session.getAttribute("user");
if(user == null){//为用户生成昵称
user = "访客" + SendMessageServlet.ONLINE_USER_COUNT;
SendMessageServlet.ONLINE_USER_COUNT ++;
session.setAttribute("user", user);
}
pageContext.setAttribute("user", user);
%> 
<html>
<head>
<title>使用 HTML5 webSocket API实现即时通讯的功能</title>
<!-- 引入CSS文件 -->
<link rel="stylesheet" type="text/css" href="ext4/resources/css/ext-all.css">
<link rel="stylesheet" type="text/css" href="ext4/shared/example.css" />
<link rel="stylesheet" type="text/css" href="css/websocket.css" />

<!-- 引入jquery库。 -->
<script type="text/javascript" src="js/jquery_1.8.3.js"></script>
<!-- 引入Ext库。-->
<script type="text/javascript" src="ext4/ext-all-debug.js"></script>
</head>

<body>
    <center><font size="4" color="red"><b>使用 HTML5 webSocket API实现即时通讯的功能！！！</b></font></center>
<div id="websocket"></div><br>
<!-- 引入webscoket js脚本文件. -->
<script type="text/javascript" src="js/websocket.js"></script>
<center><input type="button" onclick="javascript:getWindow();" value="打开WebSocket聊天窗口"></center>
<script type="text/javascript">
function getWindow(){
if($.browser.opera){//如果为谷歌浏览器，则去掉后面两个<br>。注意：在使用键盘提交信息时，谷歌浏览器会自动在原有信息的后面添加两个<br>。
Ext.onReady(function() {
Ext.MessageBox.show({ 
title:"友情提示", 
msg:"当前浏览器为Opera，使用快捷键功能前需将鼠标焦点移出文本编辑域，否则功能失效！！！", 
buttons:Ext.Msg.OKCANCEL,
width:700, 
icon:Ext.MessageBox.WARNING, 
closable:false,
fn:function(e){
if(e == 'ok'){
getWebSocketWindow('${user}');
}
}
    });
});
}else{
    getWebSocketWindow('${user}');
    }
}
</script>
</body>
</html>