Sending Dates over RMI between machines in different regions

Question

I'm having a problem sending java.util.Date objects over RMI, to and from machines in different timezones.

For example, a client in Germany will send a date object to a server in the UK.

1. User enters a date string e.g. 20090220.
2. Client app in Germany converts it to date using SimpleDateFormat("yyyyMMdd") to give: Fri Feb 20 00:00:00 CET 2009
3. Server in UK receives Date over RMI as: Thu Feb 19 23:00:00 GMT 2009
4. Server stores Date into a UK Oracle Database DATE column

What is the best way to get around this issue of incorrect dates? I could send the date string across and have the Server convert it to a Date, but I want to reduce the amount of work that the Server has to do.

Here is a stand-alone test program showing date serialisation:

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Locale;

public class SerializationTest {

    public static void main(String[] args) throws Exception {

        final String yyyyMMdd = "20090220";
        final Date date = new SimpleDateFormat("yyyyMMdd").parse(yyyyMMdd);

        if (args.length != 1) {
            System.out.println("Usage SerializationTest S|D");
        }

        boolean serialise = false;
        if (args[0].equals("S")) {
            serialise = true;
        }
        else if (args[0].equals("D")) {
            serialise = false;
        }

        String filename = "date.ser";
        if (serialise) {
            // write the object to file
            FileOutputStream fos = new FileOutputStream(filename);
            BufferedOutputStream bos = new BufferedOutputStream(fos);
            ObjectOutputStream outputStream = new ObjectOutputStream(bos);
            outputStream.writeObject(date);
            outputStream.flush();
            outputStream.close();

            System.out.println("Serialised: " + date);
        }
        else {
            FileInputStream fis = new FileInputStream(filename);
            BufferedInputStream bis = new BufferedInputStream(fis);
            ObjectInputStream inputStream = new ObjectInputStream(bis);
            Date outDate = (Date) inputStream.readObject();
            inputStream.close();

            // print the object
            System.out.println(outDate);
        }
    }
}

Answer 1

I fail to see what your problem is here, those dates look correct to me- they're just being formatted to the locale in use. If you want the date entered by the user to be in GMT, specify the locale on the SimpleDateFormat constructor

Answer 2

The Dates are actually the same. The println() is calling the toString() on date which is using the locale to format it in the local timezone.

Answer 3

Look at getTime() and setTime(). They should do what you're looking for. Instead of sending it over the wire as a location-specific string, send it as the number of milliseconds since epoch using getTime() on the client, then build a new Date on the client and use setTime() with the long value on the server.

Answer 4

Take a look at the java.util.Calendar specifically the getTime() method.

That way you will be sending the time in milliseconds rather than a String the is interpretable in different ways.