Question

I tried serializing an object using google.gson.GsonBuilder as follows:

public class JsonHelper
{
    public static String ToJson(Object o, Type oType)
    {
        Gson gson = new().setPrettyPrinting().setDateFormat("yyyy-MM-dd'T'HH:mm:ss").create();
        gson.toJson(o, oType);
    }
}

public class JsonTest
{
   public static String staticField;

   public static String ToJson()
   {
       JsonTest newJsonTest = new JsonTest();
       newJsonTest.staticField = TelephoneStatus.GetPhoneIMEI(); // let's say we use static field to keep IMEI

       Type oType = new TypeToken<JsonTest>(){}.getType();
       return JsonHelper.ToJson(newJsonTest, oType);
   }
}

Return value for JsonTest class method ToJson() is empty. If i change staticField field declaration to be non-static, it works as expected. Considering why static fields are not serialized, should it be considered as a bug? Or is it considered unnecessary?

If i had a list of JsonTest i wouldn’t expect having static field parsed and written multiple times but once. However, isn’t it better than missing it at all?

Answer 1

Java Serialization only serialize object’s non-static and non-transient fields because,

The defaultReadObject method uses information in the stream to assign
the fields of the object saved in the stream with the correspondingly
named fields in the current object. This handles the case when the
class has evolved to add new fields. The method does not need to
concern itself with the state belonging to its superclasses or
subclasses. State is saved by writing the individual fields to the
ObjectOutputStream using the writeObject method or by using the
methods for primitive data types supported by DataOutput.

Reference

In case of static field state not only belongs to any specific object it will belongs to all class.

So the static field would be comes under state of any specific object.