JSP新手问题

用TOMCAT运行时报错，奇怪的是我把里面JSP部分注释后再运行空页面不报错，再把注释去掉可以就可以运行，也能得到想要的结果，但再打开一个新页面就会再报错，请高手帮我看看
代码如下
<%@page language="java" contentType="text/html;charset=gb2312" import="javax.servlet.http.Cookie,java.util.*"%>
<html>
<head><title>response实例应用2</title></head>
<body>
<%
String userName="cookietest";
Cookie[] cookie=request.getCookies();
Cookie cookie_response=null;
List list=Arrays.asList(cookie);
Iterator it=list.iterator();while(it.hasNext())
{   
Cookie temp=(Cookie)it.next();
if(temp.getName().equals(userName+"_access_time"))
{
cookie_response=temp;
out.print("当前的时间："+new java.util.Date()+"<br>");
out.print("上一次访问的时间是："+cookie_response.getValue());
cookie_response=new Cookie(userName+"_access_time",new java.util.Date().toString());
response.addCookie(cookie_response);
break;
}
}
if(cookie_response==null)
{
cookie_response=new Cookie(userName+"_access_time",new java.util.Date().toString());
response.addCookie(cookie_response);
response.setContentType("text/html");
out.print("当前的时间："+new java.util.Date()+"<br>");
response.flushBuffer();
}
%>
</body>
</html>用TOMCAT运行报错信息
type Exception reportmessage 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
java.util.Arrays$ArrayList.<init>(Arrays.java:2342)
java.util.Arrays.asList(Arrays.java:2328)
org.apache.jsp.response2_jsp._jspService(response2_jsp.java:53)
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/5.0.30 logs.