求大侠们帮帮小女子，线程run方法里面总是出现错误，局部变量filepathString的值运行一次后指向为空了，有什么方法改

package com.proxy;

import java.net.*;
import java.io.*;

import org.htmlcleaner.CleanerProperties;
import org.htmlcleaner.DomSerializer;
import org.htmlcleaner.HtmlCleaner;
import org.htmlcleaner.PrettyHtmlSerializer;
import org.htmlcleaner.TagNode;
import org.w3c.dom.Document;

public class MyProxyServer
{
public static void main(String args[])
{
try
{
ServerSocket ss=new ServerSocket(81);
System.out.println("正在等待连接......");
while (true)
{
Socket s=ss.accept();                                               process p=new process(s);
System.out.println("连接成功");
System.out.println("********************************");
System.out.println(" ");
Thread t=new Thread(p);
t.start();
}
}
catch (Exception e)
{
System.out.println("Error:"+e);
}
}
}
class process implements Runnable
{
Socket s;
HtmlCleaner htmlCleaner;
private String toPath = "F:/";
private  static int count = 0;
private String filepathString ;
int size=10;
public process(Socket s1)
{
s=s1;
}
public void run()
{
String content=" ";
String debugerinforesult = null;
String debugers = null;

int chByte = 0;
try
{
PrintStream out=new PrintStream(s.getOutputStream());
BufferedReader in=new BufferedReader(new InputStreamReader(s.getInputStream()));

String info=in.readLine();
System.out.println(info);
debugerinforesult=in.readLine();

                 debugerinforesult+=in.readLine();

                 debugerinforesult+=in.readLine();
             debugerinforesult+=in.readLine();

     debugerinforesult+=in.readLine();

     debugerinforesult+=in.readLine();

     debugerinforesult+=in.readLine();

debugerinforesult+=in.readLine();

System.out.println("debugerinforesult "+debugerinforesult);

System.out.println("now got "+info);
int sp1=info.indexOf(' ');
int sp2=info.indexOf(' ',sp1+1);
String gotourl=info.substring(sp1,sp2); //提取URL地址
System.out.println("now connecting "+gotourl);

//URL con=new URL(gotourl);
count++;
if(true)
{
URL rootcon=new URL(gotourl);
System.out.println(gotourl);
htmlCleaner = new HtmlCleaner();
CleanerProperties props = htmlCleaner.getProperties();
TagNode tagNode = htmlCleaner.clean(rootcon);
Document document = new DomSerializer(props,true).createDOM(tagNode);
if(null == document)
{
System.out.println("Something is error!");
}
else {
System.out.println("Create Dom is Ok!");
}

// 去除文字样式
Object[] nstitle = tagNode.evaluateXPath("//title");
         for (Object tt : nstitle)
         {

         filepathString = toPath + ((TagNode) tt).getText().toString().trim() + ".xml";
       }


         Object[] nsscript = tagNode.evaluateXPath("//script");
         for (Object tt : nsscript)
         {
         ((TagNode) tt).removeFromTree();
         }
         Object[] nsimg = tagNode.evaluateXPath("//img");
         for (Object tt : nsimg)
         {
         ((TagNode) tt).removeFromTree();
         }

         Object[] nsstyle = tagNode.evaluateXPath("//style");
         for (Object tt : nsstyle)
         {
         ((TagNode) tt).removeFromTree();
         }

         Object[] nsobject = tagNode.evaluateXPath("//object");
         for (Object tt : nsobject)
         {
         ((TagNode) tt).removeFromTree();
       }

         Object[] nfont = tagNode.evaluateXPath("//font");
         for (Object tt : nfont)
         {
         ((TagNode) tt).removeFromTree();
       }
         Object[] nbody = tagNode.evaluateXPath("//body");
         for (Object tt : nbody)
         {
         ((TagNode) tt).setAttribute("style", "font-size:"+size+"pt;color:red");
       }

         Object[] nsdiv = tagNode.evaluateXPath("//div");
         for (Object tt : nsdiv)
         {
         ((TagNode) tt).removeFromTree();
       }

//文件保存成XML格式
new PrettyHtmlSerializer(props).writeToFile(tagNode, filepathString);

}
//InputStream gotoin=con.openStream(); //数据保存在这里
FileInputStream fin= new FileInputStream(filepathString);
      int n=fin.available();
byte buf[]=new byte[1024];
out.println("HTTP/1.1 200 OK");
out.println("MIME_version:1.1");
out.println("Content_Type:text/html");
out.println("Content_Length:"+n);
out.println(" ");

while ((n=fin.read(buf))>=0)
{
out.write(buf,0,n);
//outputstream.write(buf);
}
out.close();
//outputstream.close();
s.close();
count=0;
}

catch (IOException e)
{
System.out.println("Exception:"+e);
}
catch (Exception e)
{
e.printStackTrace();
}
}
}
错误提示：java.lang.NullPointerException
at java.io.FileOutputStream.<init>(FileOutputStream.java:172)
at java.io.FileOutputStream.<init>(FileOutputStream.java:70)
at org.htmlcleaner.Serializer.writeToFile(Serializer.java:131)
at org.htmlcleaner.Serializer.writeToFile(Serializer.java:154)
at org.htmlcleaner.Serializer.writeToFile(Serializer.java:164)
at com.proxy.PhoneBeanDo.createDom(PhoneBeanDo.java:137)
at com.proxy.process.run(process.java:137)
at java.lang.Thread.run(Thread.java:619)
java.lang.NullPointerException
at java.io.FileInputStream.<init>(FileInputStream.java:103)
at java.io.FileInputStream.<init>(FileInputStream.java:66)
at com.proxy.process.run(process.java:141)
at java.lang.Thread.run(Thread.java:619)

跪求大侠救救小女子，困扰了好几天了，我要把局部变量filepathString（其实是本地生成的.xml地址）的值传到移动设备端，run方法里面，第一次是成功的，以后就不行了，出现上面的错误，再次跪拜各位大侠，谢谢咯 --------------------编程问答-------------------- at com.proxy.process.run(process.java:141)
按照你贴上去的代码的格式拷贝下来，141行不可能报错，141行是个{

需要结合客户端查找原因。

补充：Java ,  Java相关