Unable to request more than once using one socket

[stoundmire]

At first, I create a socket and send various HTTP requests using this socket. But only the first request is responsed.
The behavior of the code is someting like this:

  Socket s=new Socket(host,port);
  PrintWriter out=new PrintWriter(s.getOutputStream());
  for every request{
    print the line "GET|POST uri HTTP/1.1"
    output request headers
    [output form data]
    print an empty line
    out.flush();
  }

Besides, when I use Wireshark to capture packets, it looks all the same as what I get when I visit web sites via Firefox.

But when I create seperate sockets for every request and then close them, it works.
This is my question, please help me. Thank you.

Code for PlainCookie.java
Hint: Whether create seperate sockets for every request is determined by the variable 'ev', which is set in the constructor.

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

public class PlainCookie {
	private List<String> header;
	private List<Pair> cookie;
	private Socket s=null;
	private String url;
	private int port;
	private boolean ev=true;
	public PlainCookie(String url,int port,boolean ev)throws Exception{
		header=new LinkedList<String>();
		cookie=new LinkedList<Pair>();
		this.url=url;
		this.port=port;
		this.ev=ev;
		if(!ev)
			s=new Socket(url,port);
	}
	public PlainCookie(String url,int port)throws Exception{
		this(url,port,false);
	}
	public void addHeader()throws Exception{
		BufferedReader in=new BufferedReader(new FileReader("header.txt"));
		String line;
		while((line=in.readLine())!=null){
			header.add(line);
		}
		in.close();
	}
	public void visit(String file,String post)throws Exception{
		if(ev)
			s=new Socket(url,port);
		PrintWriter out=new PrintWriter(s.getOutputStream());
		out.print(post==null?"GET":"POST");
		out.println(" /"+file+" HTTP/1.0");
		for(int k=0;k<header.size();++k)
			out.println(header.get(k));
		if(cookie.size()!=0){
			out.print("Cookie:");
			for(int k=0;k<cookie.size();++k){
				out.print(" "+cookie.get(k).name+"="+cookie.get(k).value);
				if(k<cookie.size()-1)
					out.print(";");
			}
			out.println();
		}
		if(post!=null){
			out.println("Content-Type: application/x-www-form-urlencoded");
			out.println("Content-Length: "+post.length());
			out.println();
			out.print(post);
		}
		else{
			out.println();
		}
		out.flush();
		out.flush();
		BufferedReader in=new BufferedReader(new InputStreamReader(s.getInputStream()));
		String line,body;
		StringBuilder sb=new StringBuilder();
		while((line=in.readLine())!=null){
			if(line.length()==0)
				break;
			if(line.startsWith("Set-Cookie")){
				line=line.substring("Set-Cookie: ".length());
				StringTokenizer st1=new StringTokenizer(line,"; ");
				while(st1.hasMoreTokens()){
					String pt=st1.nextToken(),name,value;
					if(pt.startsWith("path"))
						continue;
					StringTokenizer st2=new StringTokenizer(pt,"=");
					name=st2.nextToken();
					value=st2.nextToken();
					cookie.add(new Pair(name,value));
				}
			}
		}
		while((line=in.readLine())!=null){
			sb.append(line);
			sb.append('\n');
		}
		body=sb.toString();
		System.out.println(body.indexOf("Nobody")+"\t"+body.indexOf("stoundmire"));
		if(ev)
			s.close();
	}
	public void close()throws Exception{
		if(!ev)
			s.close();
	}
	class Pair{
		String name;
		String value;
		public Pair(String name,String value){
			this.name=name;
			this.value=value;
		}
	}
	public static void main(String[] args){
		PlainCookie hp=null;
		try{
			hp=new PlainCookie("acm.hrbeu.edu.cn",80,true);
			hp.addHeader();
			hp.visit("index.php",null);
			Thread.sleep(500);hp.visit("index.php?act=cp",null);
		}
		catch(Exception ex){
			ex.printStackTrace(System.err);
		}
		finally{
			try{
				if(hp!=null)
					hp.close();
			}
			catch(Exception ex){
				ex.printStackTrace(System.err);
			}
		}
	}
}

And contents for header.txt

Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, application/x-shockwave-flash, application/x-silverlight, application/x-ms-application, application/x-ms-xbap, application/vnd.ms-xpsdocument, application/xaml+xml, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, */*
Accept-Language: zh-cn
UA-CPU: x86
Accept-Encoding: gzip, deflate
User-Agent: Mozilla/4.0
Host: acm.hrbeu.edu.cn
Connection: Keep-Alive

[travishein]

you appear to be explicitly closing the socket at the end of visit();

private boolean ev=true;
//...

public void visit(String file,String post)throws Exception{
//...
  if(ev)
    s.close();
}