خواندن و نوشتن در فایل xml

با سلام من یه فایل xml دارم که تو پوشه assets ذخیره کردم میتونم از رو فایل بخونم  از طریق xmlpullparserولی وقتی تغییر میدم تو فایل ذخیره نمیشه خیلی سرچ کردم و امتحان کردم نمیشه کمکم کنید خواهشا

   public String readFeed(InputStream is) throws XmlPullParserException, IOException {
        XmlPullParserFactory factory;
        XmlPullParser parser = null;

        factory = XmlPullParserFactory.newInstance();
        factory.setNamespaceAware(true);
        parser = factory.newPullParser();

        parser.setInput(is, null);
        String dbvar;
        dbvar = new String();

        int eventType = parser.getEventType();
        Log.i("event", "" + eventType);

        while (eventType != XmlPullParser.END_DOCUMENT)
        {
            String tagname = parser.getName();

            switch (eventType)
            {
                case XmlPullParser.START_TAG:

                    if (tagname.equalsIgnoreCase("dbxml")) {
                        // create a new instance of Student
                        dbxml = new dbxml();
                    }
                    break;

                case XmlPullParser.TEXT:
                    text = parser.getText();
                    break;

                case XmlPullParser.END_TAG:
                    if (tagname.equalsIgnoreCase("dbxml")) {
                        // add Student object to list
                        //  students.add(Student);
                        // Student.(text);
                    }
                    else if (tagname.equalsIgnoreCase("server"))
                    {
                        dbxml.setServer(text);
                        Log.i("server", tagname);
                    }
                    else if (tagname.equalsIgnoreCase("db"))
                    {
                        dbxml.setDb(text);
                        Log.i("db", tagname);
                    }
                    else if (tagname.equalsIgnoreCase("user"))
                    {
                        dbxml.setUser(text);
                        Log.i("user", tagname);
                    }
                    else if (tagname.equalsIgnoreCase("pass"))
                    {
                        dbxml.setPass(text);
                        Log.i("pass", tagname);
                    }

                    break;

                default:
                    break;
            }
            eventType = parser.next();
        }

        return dbvar;
    }

   try {
            // XmlPullParser parser = null;
            xpp = new XMLPullParserHandle();
            xpp.readFeed(getAssets().open("database.xml"));

  String newxmlfile = "database.xml";
            //Log.i("dir", "" + outfilename);

            try {  
                FileOutputStream fileos = openFileOutput(newxmlfile + "database.xml", Context.MODE_WORLD_WRITEABLE);
                Log.i("write", "" + fileos);
                XmlSerializer xmlSerializer = Xml.newSerializer();
                StringWriter writer = new StringWriter();
                xmlSerializer.setOutput(writer);
                xmlSerializer.startDocument("UTF-8", true);
                xmlSerializer.startTag("", "dbvar");
                xmlSerializer.startTag("", "dbxml");
                xmlSerializer.startTag("", "server");
                xmlSerializer.text(sqldb.server);
                Log.i("write", sqldb.server);
                xmlSerializer.endTag("", "server");
                xmlSerializer.startTag("", "db");
                xmlSerializer.text(sqldb.db);
                Log.i("write", sqldb.db);
                xmlSerializer.endTag("", "db");
                xmlSerializer.startTag("", "user");
                xmlSerializer.text(sqldb.user);
                Log.i("write", sqldb.user);
                xmlSerializer.endTag("", "user");
                xmlSerializer.startTag("", "pass");
                xmlSerializer.text(sqldb.pass);
                Log.i("write", sqldb.pass);
                xmlSerializer.endTag("", "pass");
                xmlSerializer.endTag("", "dbxml");
                xmlSerializer.endTag("", "dbvar");
                xmlSerializer.endDocument();
                xmlSerializer.flush();
                String dataWrite = writer.toString();
                fileos.write(dataWrite.getBytes());
                Log.i("writeinfile", "" + dataWrite.getBytes());
                fileos.close();
                xpp.readFeed(getAssets().open("database.xml"));
            }

            catch (FileNotFoundException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

            catch (IllegalArgumentException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            catch (IllegalStateException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            catch (XmlPullParserException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }

 }

 catch (XmlPullParserException e) {
 // TODO Auto-generated catch block
 e.printStackTrace();
 }
 catch (IOException e) {
 // TODO Auto-generated catch block
 e.printStackTrace();
 }

 logcat
08-12 10:44:42.651: I/server(6575): server
08-12 10:44:42.651: I/db(6575): db
08-12 10:44:42.661: I/user(6575): user
08-12 10:44:42.661: I/pass(6575): pass
08-12 10:44:42.661: I/xppkjnfdlka(6575): 10.0.2.2saa
08-12 10:44:42.661: I/LOG(6575): sql_server: 10.0.2.2, sql_db: SAHBA sql_user:sasql_pass123
08-12 10:44:42.671: I/write(6575): java.io.FileOutputStream@44f35f78
08-12 10:44:42.711: I/write(6575): 10.0.2.2
08-12 10:44:42.711: I/write(6575): SAHBA 
08-12 10:44:42.711: I/write(6575): sa
08-12 10:44:42.711: I/write(6575): 123
08-12 10:44:42.711: I/writeinfile(6575): [B@44f81b98