php - File is not being uploaded properly -

in android app, i've upload file server , read file @ server side. file being uploaded times happen, in folder (at server in file resides) if uploaded file exists, current uploaded file generated previous file data. e.g. if upload file named a server data '1, 2 , 3' there file a.txt under folder @ server side same data, , if upload file named b server data 'a, b , c' file b.txt under folder there previous file data of a.txt. in b.txt, data '1, 2 , 3'. below code. can issue?

android side

public void uploaduserfriendid(string user_id, string filepath, string filename)     {         string server_url = "http://addressofserver/folder/myfile.php";         inputstream inputstream;         try         {             inputstream = new fileinputstream(new file(filepath));             byte[] data;             try             {                 data = ioutils.tobytearray(inputstream);                  httpclient httpclient = new defaulthttpclient();                  httpclient.getparams().setparameter(coreprotocolpnames.user_agent,                         system.getproperty("http.agent"));                    httppost httppost = new httppost(server_url);                 inputstreambody inputstreambody = new inputstreambody(new bytearrayinputstream(data), filename);                 multipartentity multipartentity = new multipartentity();                 multipartentity.addpart("file", inputstreambody);                 multipartentity.addpart("user_id", new stringbody(user_id));                  httppost.setentity(multipartentity);                 httpresponse httpresponse = httpclient.execute(httppost);                    // handle response script.                 if(httpresponse != null) {                     //toast.maketext(getbasecontext(),  "upload completed. ", 2000).show();                  } else { // error, no response.                     //toast.maketext(getbasecontext(),  "server error. ", 2000).show();                 }             } catch (ioexception e) {                 e.printstacktrace();             }         } catch (filenotfoundexception e1) {             e1.printstacktrace();         }     } 

php side

<?php   error_reporting(~0);   ini_set('display_errors', 1);      mysql_connect("localhost", "root", "admin@123") or die(mysql_error()) ;      mysql_select_db("retail_menu") or die(mysql_error()) ;        $today =date("ymdhis");     $pic=$today.".txt";      if (isset($_post["user_id"]) && !empty($_post["user_id"]))     {         $user_id=$_post['user_id'];      }     else     {           $user_id="null";      }      $objfile = & $_files["file"];      // here file created under folder named upload @ server side     if( move_uploaded_file( $objfile["tmp_name"], "upload/".$user_id.".txt" ) )     {          $file = fopen("upload/".$user_id.".txt" ,"r");          while(! feof($file))         {             $friend_id = fgets($file, 8192);             if($friend_id!= null)             {                 $query = "insert ignore table_name (user_id, friend_id) values('$user_id', '$friend_id')";                 var_dump($query);                 mysql_query($query);              }         }             fclose($file);     }       else      {         print "there error uploading file, please try again!";     }   ?>