HTTP Status 500 求大神帮忙

按照书上写的代码 不是知道为啥总是出现 HTTP Status 500 错误
代码如下：

cookie.jsp
<%@ page language="java" import="java.util.*" pageEncoding="gb2312"%>

<%
String str="12";
int number=Integer.parseInt(str);
%>
该数的平方为：<%=number*number %>

<%
Cookie cookie=new Cookie("number",str);
cookie.setMaxAge(600);
response.addCookie(cookie);
%>
到达cookie1

cookie1.jsp
<%@ page language="java" import="java.util.*" pageEncoding="gb2312"%>

<%
String str=null;
Cookie[] cookies=request.getCookies();
for(int i=0;i {
if(cookies[i].getName().equals("number"))
{
str=cookies[i].getValue();
break;
}
}
int number=Integer.parseInt(str);
%>
该数的立方为：<%=number*number*number %>

错误显示为：
HTTP Status 500 -

---

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:541)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:435)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)

root cause

java.lang.NullPointerException
org.apache.jsp.cookie1_jsp._jspService(cookie1_jsp.java:61)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:393)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)

note The full stack trace of the root cause is available in the Apache Tomcat/6.0.13 logs.

---

Apache Tomcat/6.0.13

求大神帮忙啊

这句改一下

.equals("number")

"number".equals(cookies[i].getName())

这句加个判断

if(str!= null){
    int number=Integer.parseInt(str);
 }

这两个地方可能会有空指针

用debug执行，给jsp第一行加个断点，f8或者f6，快捷键可能会不同，一行行执行，就知道哪一行报错了。

空指针异常，给你报错的类了，也指出了错误出现在哪一行，楼主去看看那一行使用的对象，什么对象是空的