Location based Timezone Retrieval

Given: LDAP stores location of users.

How do I drive their timezones using their location? Any pointers are accepted, Java langua开发者_如何学Goge preferred.

Thanks in advance.

This depends on information the "location" contains? You'd somehow need to map the location to a timezone name, preferably the Olson style timezone names, because they are more detailed and easier to map, as they are locations themselves.

If it's an approximate addres (like country and city or so) then several geolocation services do include timezones in their information, so you can call these services and see.

If it's a geolocation with latitude and longitude then a site called Earthtools can give you the timezone. http://www.earthtools.org/webservices.htm#timezone

There is this database that provides mappings from cities and countries to timezones: http://citytimezones.info/cms/pending_requests.htm

Unfortunately it uses Windows timezone names, but you can this data http://unicode.org/repos/cldr/trunk/common/supplemental/windowsZones.xml from Unicode.org to map between Windows timezone names and the Olson TZ names.

I haven't actually done this but the following should work:

1. You can first use GeoGoogle java library to get the longitude/latitude from the city-state-country.

2. Next, you can use EarthTools (and some java code of your own) mentioned by Lennart to get the timezone :)

We are using the MaxMind GeoIP database to get information regarding the location of a user. They have a paid version (99.8% accuracy) as well as a free version (99.5% accuracy).

They also provide you with APIs in Java, C, PHP etc that will enable you to query its database which you can download and keep locally (updates provided each month). The database provides you info regarding the client city, state, country etc on the basis of IP addresses.

Hope this helps.

 Try this code for use Google Time Zone API from Java:

String get_xml_server_reponse(String server_url){

    URL xml_server = null;

    String xmltext = "";

    InputStream input;


    try {
        xml_server = new URL(server_url);


        try {
            input = xml_server.openConnection().getInputStream();


            final BufferedReader reader = new BufferedReader(new InputStreamReader(input));
            final StringBuilder sBuf = new StringBuilder();

            String line = null;
            try {
                while ((line = reader.readLine()) != null) 
                {
                    sBuf.append(line);
                }
               } 
            catch (IOException e) 
              {
                    Log.e(e.getMessage(), "XML parser, stream2string 1");
              } 
            finally {
                try {
                    input.close();
                    }
                catch (IOException e) 
                {
                    Log.e(e.getMessage(), "XML parser, stream2string 2");
                }
            }

            xmltext =  sBuf.toString();

        } catch (IOException e1) {

                e1.printStackTrace();
            }


        } catch (MalformedURLException e1) {

          e1.printStackTrace();
        }

     return  xmltext;

  }     


 private String get_UTC_Datetime_from_timestamp(long timeStamp){

    try{

        Calendar cal = Calendar.getInstance();
        TimeZone tz = cal.getTimeZone();

        int tzt = tz.getOffset(System.currentTimeMillis());

        timeStamp -= tzt;

        // DateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss",Locale.getDefault());
        DateFormat sdf = new SimpleDateFormat();
        Date netDate = (new Date(timeStamp));
        return sdf.format(netDate);
    }
    catch(Exception ex){
        return "";
     }
    } 

 class NTP_UTC_Time
 {
     private static final String TAG = "SntpClient";

     private static final int RECEIVE_TIME_OFFSET = 32;
     private static final int TRANSMIT_TIME_OFFSET = 40;
     private static final int NTP_PACKET_SIZE = 48;

     private static final int NTP_PORT = 123;
     private static final int NTP_MODE_CLIENT = 3;
     private static final int NTP_VERSION = 3;

     // Number of seconds between Jan 1, 1900 and Jan 1, 1970
     // 70 years plus 17 leap days
     private static final long OFFSET_1900_TO_1970 = ((365L * 70L) + 17L) * 24L * 60L * 60L;

     private long mNtpTime;

     public boolean requestTime(String host, int timeout) {
         try {
             DatagramSocket socket = new DatagramSocket();
             socket.setSoTimeout(timeout);
             InetAddress address = InetAddress.getByName(host);
             byte[] buffer = new byte[NTP_PACKET_SIZE];
             DatagramPacket request = new DatagramPacket(buffer, buffer.length, address, NTP_PORT);

             buffer[0] = NTP_MODE_CLIENT | (NTP_VERSION << 3);

             writeTimeStamp(buffer, TRANSMIT_TIME_OFFSET);

             socket.send(request);

             // read the response
             DatagramPacket response = new DatagramPacket(buffer, buffer.length);
             socket.receive(response);          
             socket.close();

             mNtpTime = readTimeStamp(buffer, RECEIVE_TIME_OFFSET);            
         } catch (Exception e) {
           //  if (Config.LOGD) Log.d(TAG, "request time failed: " + e);
             return false;
         }

         return true;
     }


     public long getNtpTime() {
         return mNtpTime;
     }


     /**
      * Reads an unsigned 32 bit big endian number from the given offset in the buffer.
      */
     private long read32(byte[] buffer, int offset) {
         byte b0 = buffer[offset];
         byte b1 = buffer[offset+1];
         byte b2 = buffer[offset+2];
         byte b3 = buffer[offset+3];

         // convert signed bytes to unsigned values
         int i0 = ((b0 & 0x80) == 0x80 ? (b0 & 0x7F) + 0x80 : b0);
         int i1 = ((b1 & 0x80) == 0x80 ? (b1 & 0x7F) + 0x80 : b1);
         int i2 = ((b2 & 0x80) == 0x80 ? (b2 & 0x7F) + 0x80 : b2);
         int i3 = ((b3 & 0x80) == 0x80 ? (b3 & 0x7F) + 0x80 : b3);

         return ((long)i0 << 24) + ((long)i1 << 16) + ((long)i2 << 8) + (long)i3;
     }

     /**
      * Reads the NTP time stamp at the given offset in the buffer and returns 
      * it as a system time (milliseconds since January 1, 1970).
      */    
     private long readTimeStamp(byte[] buffer, int offset) {
         long seconds = read32(buffer, offset);
         long fraction = read32(buffer, offset + 4);
         return ((seconds - OFFSET_1900_TO_1970) * 1000) + ((fraction * 1000L) / 0x100000000L);        
     }

     /**
      * Writes 0 as NTP starttime stamp in the buffer. --> Then NTP returns Time OFFSET since 1900
      */    
     private void writeTimeStamp(byte[] buffer, int offset) {        
         int ofs =  offset++;

         for (int i=ofs;i<(ofs+8);i++)
           buffer[i] = (byte)(0);             
     }

 }

 String get_time_zone_time(GeoPoint gp){

        String erg = "";
        String raw_offset = "";
        String dst_offset = "";

        double Longitude = gp.getLongitudeE6()/1E6;
        double Latitude = gp.getLatitudeE6()/1E6;

        // String request = "http://ws.geonames.org/timezone?lat="+Latitude+"&lng="+ Longitude+ "&style=full";


        long tsLong = 0; // System.currentTimeMillis()/1000;

        NTP_UTC_Time client = new NTP_UTC_Time();

        if (client.requestTime("pool.ntp.org", 2000)) {              
          tsLong = client.getNtpTime();
        }

        if (tsLong != 0)
        {

        tsLong = tsLong  / 1000;

        // https://maps.googleapis.com/maps/api/timezone/xml?location=39.6034810,-119.6822510&timestamp=1331161200&sensor=true

        String request = "https://maps.googleapis.com/maps/api/timezone/xml?location="+Latitude+","+ Longitude+ "&timestamp="+tsLong +"&sensor=true";

        String xmltext = get_xml_server_reponse(request);

        if(xmltext.compareTo("")!= 0)
        {

         int startpos = xmltext.indexOf("<TimeZoneResponse");
         xmltext = xmltext.substring(startpos);



        XmlPullParser parser;
        try {
            parser = XmlPullParserFactory.newInstance().newPullParser();


             parser.setInput(new StringReader (xmltext));

             int eventType = parser.getEventType();  

             String tagName = "";


             while(eventType != XmlPullParser.END_DOCUMENT) {
                 switch(eventType) {

                     case XmlPullParser.START_TAG:

                           tagName = parser.getName();

                         break;


                     case XmlPullParser.TEXT :


                        if  (tagName.equalsIgnoreCase("raw_offset"))
                          if(raw_offset.compareTo("")== 0)                               
                            raw_offset = parser.getText();  

                        if  (tagName.equalsIgnoreCase("dst_offset"))
                          if(dst_offset.compareTo("")== 0)
                            dst_offset = parser.getText();  


                        break;   

                 }

                 try {
                        eventType = parser.next();
                    } catch (IOException e) {

                        e.printStackTrace();
                    }

                }

                } catch (XmlPullParserException e) {

                    e.printStackTrace();
                    erg += e.toString();
                }

        }      

        int ro = 0;
        if(raw_offset.compareTo("")!= 0)
        { 
            float rof = str_to_float(raw_offset);
            ro = (int)rof;
        }

        int dof = 0;
        if(dst_offset.compareTo("")!= 0)
        { 
            float doff = str_to_float(dst_offset);
            dof = (int)doff;
        }

        tsLong = (tsLong + ro + dof) * 1000;



        erg = get_UTC_Datetime_from_timestamp(tsLong);
        }


  return erg;

}

And use it with:

GeoPoint gp = new GeoPoint(39.6034810,-119.6822510);
String Current_TimeZone_Time = get_time_zone_time(gp);