为什么取出来第一个有值，后面都为NULL

protected void doPost(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
System.out.println(req.getParameter("initArgs"));
HttpSession session = req.getSession();
String server = req.getParameter("server");
//String command = req.getParameter("command");
//System.out.println(command);
LoadConfig load = new LoadConfig();
Properties properties = load.getServerArgs();

URL url = new URL(load.getServer(server));
HttpURLConnection connection = (HttpURLConnection)url.openConnection();
//String info = "";
try{
connection.setDoOutput(true);
connection.setDoInput(true);
connection.setUseCaches(false);
connection.setRequestProperty("Content-type", "application/x-java-serialized-object"); 
connection.setRequestProperty("accept", "text/xml;text/html");   
        connection.setRequestProperty("Content-Type", "text/xml;charset=utf-8");  
        connection.setRequestMethod("POST"); 
        connection.connect();   
        
synchronized (this) {
os = new OutputStreamWriter(connection.getOutputStream(),"utf-8");
String key = load.getKey("key");
Date date = new Date();
String time = ""+date.getTime(); 
String md5Code = new Md5().getMd5((time+key).getBytes()); 
System.out.println("请求的MD5:  "+md5Code);
Iterator it = properties.entrySet().iterator();
String command = "";


String info = "";
List commandlist = new ArrayList();  
int i = 1;
while(it.hasNext()){

System.out.println("正在初始化第"+i+"条配置");
Map.Entry entry=(Map.Entry)it.next();
command = "setServerConfig "+entry.getKey()+" "+entry.getValue();
os.write("command="+command+"&time="+time+"&flag="+md5Code);
//System.out.println("本次请求参数: command="+command+"&time="+time+"&flag="+md5Code);
    os.flush();
    
    is = connection.getInputStream();   
br= new BufferedReader(new InputStreamReader(is)); 


if((info = br.readLine())!= null){
System.out.println(info); //这里第一次有值，后面全为NULL了
commandlist.add(info);
session.setAttribute("commandlist", commandlist); 

}  
this.wait(500);
    i++;
    command= "";
}
  
  
}