在response中使用Cookie，求助！

Question

<%@page import="javax.servlet.http.Cookie.java.util.*"%>
<%
String username="liuning"
Cookie[] cookie=request.getCookies();
Cookie cookie_response=null;
List list=Arrays.asList(cookie);//query List,Attays
Iterator it=list.iterator();//query Iterator
while(it.hasNext())
{
Cookie temp=(Cookie)it.next();
if(temp.getName().equals(userName+"_access_time"))
{
cooke_response=temp;
break; }
}
out.println("now"+new java.util.Date()+"<br>");
if(cookie_response!=null)
{
out.println("last time you visited:"+cookie_response.getValue());
cookie_response.setValue(new Date().toString());
}
else
{
cooke_response=new Cookie(username+"_access_time",new java.util.Date().toString());
}
response.addCookie(cookie_response);
response.setContentType("test/heml");
response.flushBuffer();
%>报错：
HTTP Status 500 - --------------------------------------------------------------------------------type Exception reportmessage description The server encountered an internal error () that prevented it from fulfilling this request.exception org.apache.jasper.JasperException: Exception in JSP: /response.jsp:63: String username="liuning";
4: Cookie[] cookie=request.getCookies();
5: Cookie cookie_response=null;
6: List list=Arrays.asList(cookie);//query List,Attays
7: Iterator it=list.iterator();//query Iterator
8: while(it.hasNext())
9: {
Stacktrace:
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:506)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:395)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:314)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:264)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
root cause java.lang.NullPointerException
java.util.Arrays$ArrayList.<init>(Arrays.java:3357)
java.util.Arrays.asList(Arrays.java:3343)
org.apache.jsp.response_jsp._jspService(response_jsp.java:50)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:97)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:334)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:314)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:264)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
note The full stack trace of the root cause is available in the Apache Tomcat/5.5.20 logs.请高手赐教！

Answer 1

Cookie[] cookie=request.getCookies();
你测试一下你的cookie.length属性是不是为0
可能是这出的问题

Answer 2

aifei_africa,该怎么测试啊？
我在<%...
Cookie[] cookie=request.getCookies();
out.println(cookie.length);//新加入
Cookie cookie_response=null;
...
%>
仍报错
type Exception reportmessage description The server encountered an internal error () that prevented it from fulfilling this request.exception org.apache.jasper.JasperException: Exception in JSP: /response.jsp:52: <%
3: String username="liuning";
4: Cookie[] cookie=request.getCookies();
5: out.println(cookie.length);
6: Cookie cookie_response=null;
7: List list=Arrays.asList(cookie);//query List,Arrays
8: Iterator it=list.iterator();//query IteratorStacktrace:
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:506)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:395)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:314)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:264)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
root cause java.lang.NullPointerException
java.util.Arrays$ArrayList.<init>(Arrays.java:3357)
java.util.Arrays.asList(Arrays.java:3343)
org.apache.jsp.response_jsp._jspService(response_jsp.java:50)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:97)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:334)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:314)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:264)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)

Answer 3

我在java标准api包中为什么查不到cookie呢？