How to serialize static data members of a Java class?

When we serialize objects, static members are not serialized, but if we need to do so, is there any way out?

Solution 1:

The first question is why you need to serialize the static members?

Static members are associated with the class, not the instances, so it does not make sense to include them when serializing an instance.

The first solution is to make those members not static. Or, if those members are the same in the original class and the target class (same class, but possibly different runtime environments), don't serialize them at all.

I have a few thoughts on how one could send across static members, but I first need to see the use case, as in all cases that means updating the target class, and I haven't found a good reason to do so.

Solution 2:

Folks, static doesn't mean IMMUTABLE. For instance, I may want to serialize the whole state of the computation (yes, including static fields -- counters, etc) to resume later, after JVM and/or host computer restarted.

The right answer to that, as already said, is to use Externalizable, not Serializable, interface. Then you have a complete control on what and how you externalize.

Solution 3:

This is serialization for the static field: newBookingNumber.

class Booking implements Serializable
{

    /**
     * Generated serial version ID.
     */

    private static final long serialVersionUID = 5316748056989930874L;

    // To hold new booking number.
    private static int newBookingNumber = 0;

    // The booking number.
    private int bookingNumber;


    /* 
     * Default serializable fields of a class are defined to be 
     * the non-transient and non-static fields. So, we have to 
     * write and read the static field separately.
     */
    private void writeObject(ObjectOutputStream oos)
        throws IOException 
    {
        oos.defaultWriteObject();
        oos.writeObject(new Integer(newBookingNumber));
    }

    private void readObject(ObjectInputStream ois)
    throws ClassNotFoundException, IOException 
    {
        ois.defaultReadObject();
        newBookingNumber = (Integer)ois.readObject();
    }
}