com.google.gwt.user.client.rpc.SerializationException: why is my class not Serializable

Question

I am running into this error when I load my GWT page:

error com.google.gwt.user.client.rpc.SerializationException: Type 'com.summerbreezemotel.server.DBReservation' was not included in the set of types which can be serialized by this SerializationPolicy or its Class object could not be loaded.

I looked at the docs and seemed to follow all the constraints. I also have 3 other classes which do the same thing however this one seems to cause an issue. Any help would be appreciated.

the class which is failing:DBReservation

    package com.summerbreezemotel.server;
    import java.util.Date;

    import com.google.appengine.api.datastore.DatastoreService;
    import com.google.appengine.api.datastore.DatastoreServiceFactory;
    import com.google.appengine.api.datastore.Entity;
    import com.google.appengine.api.datastore.Key;
    import com.google.appengine.api.datastore.KeyFactory;
    import com.summerbreezemotel.shared.DataReservation;
    import com.summerbreezemotel.shared.SiteConstants;

    public class DBReservation extends DataReservation
    {
      /**
       * 
       */
      private static final long serialVersionUID = 146606067638056872L;
      Date dateReserved;
      String userEmail;

      public DBReservation() {}

      public DBReservation(DataReservation in) {
        checkIn = in.checkIn;
        checkOut = in.checkOut;
        form_FirstName = in.form_FirstName;
        form_LastName = in.form_LastName;
        form_Addr1 = in.form_Addr1;
        form_Addr2 = in.form_Addr2;
        form_City = in.form_City;
        form_State = in.form_State;
        form_Zip = in.form_Zip;
        form_Country = in.form_Country;
        form_Phone = in.form_Phone;
        form_Email = in.form_Email;
        form_CardType = in.form_CardType;
        form_CardMonth = in.form_CardMonth;
        form_CardNumber = in.form_CardNumber;
        form_CardYear = in.form_CardYear;
        form_RoomType = in.form_RoomType;
        form_isSmoking = in.form_isSmoking;
        form_numRooms = in.form_numRooms;
        ratePerNightPerRoom = in.ratePerNightPerRoom;
        totalRate = in.totalRate;   
      }

      DataReservation getData()
      {
        DataReservation out = new DataReservation();
        out.checkIn = checkIn;
        out.checkOut = checkOut;
        out.form_FirstName = form_FirstName;
        out.form_LastName = form_LastName;
        out.form_Addr1 = form_Addr1;
        out.form_Addr2 = form_Addr2;
        out.form_City = form_City;
        out.form_State = form_State;
        out.form_Zip = form_Zip;
        out.form_Country = form_Country;
        out.form_Phone = form_Phone;
        out.form_Email = form_Email;
        out.form_CardType = form_CardType;
        out.form_CardMonth = form_CardMonth;
        out.form_CardNumber = form_CardNumber;
        out.form_CardYear = form_CardYear;
        out.form_RoomType = form_RoomType;
        out.form_isSmoking = form_isSmoking;
        out.form_numRooms = form_numRooms;
        out.ratePerNightPerRoom = ratePerNightPerRoom;
        out.totalRate = totalRate;
        return out;
      }

      // gets item from DB and convertes it to this
      void fillReservationFromEntity(Entity item)
      {
        userEmail = (String) item.getProperty(SiteConstants.USER_PROPERTY);
        dateReserved = (Date) item.getProperty(SiteConstants.RESERVE_DATE_PROPERTY);
        checkIn = (Date) item.getProperty(SiteConstants.IN_DATE_PROPERTY);
        checkOut = (Date) item.getProperty(SiteConstants.OUT_DATE_PROPERTY);
        form_FirstName = (String) item.getProperty(SiteConstants.FORM_FIRSTNAME_PROPERTY);
        form_LastName = (String) item.getProperty(SiteConstants.FORM_LASTNAME_PROPERTY);
        form_Addr1 = (String) item.getProperty(SiteConstants.FORM_ADDR1_PROPERTY);
        form_Addr2 = (String) item.getProperty(SiteConstants.FORM_ADDR2_PROPERTY);
        form_City = (String) item.getProperty(SiteConstants.FORM_CITY_PROPERTY);
        form_State = (String) item.getProperty(SiteConstants.FORM_STATE_PROPERTY);
        form_Zip = (String) item.getProperty(SiteConstants.FORM_ZIP_PROPERTY);
        form_Country = (String)item.getProperty(SiteConstants.FORM_COUNTRY_PROPERTY);
        form_Phone = (String) item.getProperty(SiteConstants.FORM_PHONE_PROPERTY);
        form_Email = (String) item.getProperty(SiteConstants.FORM_EMAIL_PROPERTY);
        form_CardType = (String) item.getProperty(SiteConstants.FORM_CARDTYPE_PROPERTY);
        form_CardMonth = (String) item.getProperty(SiteConstants.FORM_CARDMONTH_PROPERTY);
        form_CardNumber = (String) item.getProperty(SiteConstants.FORM_CARDNUMBER_PROPERTY);
        form_CardYear = (Long) item.getProperty(SiteConstants.FORM_CARDYEAR_PROPERTY);
        form_RoomType = (Long) item.getProperty(SiteConstants.FORM_ROOMTYPE_PROPERTY);
        form_isSmoking = (Boolean) item.getProperty(SiteConstants.FORM_ISSMOKING_PROPERTY);
        form_numRooms = (Long) item.getProperty(SiteConstants.FORM_NUMROOMS_PROPERTY);
        ratePerNightPerRoom = (Double) item.getProperty(SiteConstants.RATEPERNIGHTPERROOM_PROPERTY);
        totalRate = (Double) item.getProperty(SiteConstants.TOTALRATE_PROPERTY);
      }

      void addReservationsToEntity(Entity item)
      {
        item.setProperty(SiteConstants.USER_PROPERTY, userEmail);
        item.setProperty(SiteConstants.RESERVE_DATE_PROPERTY, dateReserved);
        item.setProperty(SiteConstants.IN_DATE_PROPERTY, checkIn);
        item.setProperty(SiteConstants.OUT_DATE_PROPERTY, checkOut);
        item.setProperty(SiteConstants.FORM_FIRSTNAME_PROPERTY,form_FirstName);
        item.setProperty(SiteConstants.FORM_LASTNAME_PROPERTY,form_LastName);
        item.setProperty(SiteConstants.FORM_ADDR1_PROPERTY,form_Addr1);
        item.setProperty(SiteConstants.FORM_ADDR2_PROPERTY,form_Addr2);
        item.setProperty(SiteConstants.FORM_CITY_PROPERTY,form_City);
        item.setProperty(SiteConstants.FORM_STATE_PROPERTY,form_State);
        item.setProperty(SiteConstants.FORM_ZIP_PROPERTY,form_Zip);
        item.setProperty(SiteConstants.FORM_COUNTRY_PROPERTY,form_Country);
        item.setProperty(SiteConstants.FORM_PHONE_PROPERTY,form_Phone);
        item.setProperty(SiteConstants.FORM_EMAIL_PROPERTY,form_Email);
        item.setProperty(SiteConstants.FORM_CARDTYPE_PROPERTY,form_CardType);
        item.setProperty(SiteConstants.FORM_CARDMONTH_PROPERTY,form_CardMonth);
        item.setProperty(SiteConstants.FORM_CARDNUMBER_PROPERTY,form_CardNumber);
        item.setProperty(SiteConstants.FORM_CARDYEAR_PROPERTY,form_CardYear);
        item.setProperty(SiteConstants.FORM_ROOMTYPE_PROPERTY,form_RoomType);
        item.setProperty(SiteConstants.FORM_ISSMOKING_PROPERTY,form_isSmoking);
        item.setProperty(SiteConstants.FORM_NUMROOMS_PROPERTY,form_numRooms);
        item.setProperty(SiteConstants.RATEPERNIGHTPERROOM_PROPERTY,ratePerNightPerRoom);
        item.setProperty(SiteConstants.TOTALRATE_PROPERTY,totalRate);
      }

      void store()
      {
    //      UserService userService = UserServiceFactory.getUserService();
    //      User user = userService.getCurrentUser();
    //      if(user.getEmail() != null)
    //          userEmail = user.getEmail();

        DatastoreService datastore = DatastoreServiceFactory.getDatastoreService();

        String SummerBreezeDateStoreName = new String(SiteConstants.KEY_NAME);
        Key SummerBreezeDateStoreKey = KeyFactory.createKey(SiteConstants.KEY_KEY, SummerBreezeDateStoreName);
        Entity reservationsEntry = new Entity(SiteConstants.DB_RESERVATIONS, SummerBreezeDateStoreKey);

        addReservationsToEntity(reservationsEntry);
        datastore.put(reservationsEntry);
        // use this if writes get to high
        //      item.setProperty("testBlob",new Blob(toByte(roomResevationRequest)));

        datastore.put(reservationsEntry);
      }
    }

my DataReservation

      package com.summerbreezemotel.shared;

      import java.io.Serializable;
      import java.util.Date;

      public class DataReservation implements Serializable
      {
        private static final long serialVersionUID = -7598404617383692994L;

        public String form_FirstName;
        public String form_LastName;
        public String form_Addr1;
        public String form_Addr2;
        public String form_City;
        public String form_State;
        public String form_Zip;
        public String form_Country;
        public String form_Phone;
        public String form_Email;
        public String form_CardType;
        public String form_CardMonth;
        public String form_CardNumber;
        public long form_CardYear;
        public long form_RoomType;
        public boolean form_isSmoking;
        public Date checkIn;
        public Date checkOut;
        public long form_numRooms;
        public double ratePerNightPerRoom;
        public double totalRate;

        public DataReservation()
        {   
        }
      }

Answer 1

I think this is a typical case of shooting yourself in the foot. By extending your server object with the logic from the shared class you made is somewhat easier to create a server side class including the database code, but if you by accident return the server side instead instead of calling getData() just before sending it to the client you get the server side class which can´t be send to the client of course. But the compiler won't warn you for it because it syntactical correct. So I believe the answer is not in the code given, that looks good, but in between the gwt servlet and the usage of DBReservation.

Answer 2

You are using a file in shared folder that implements Serializable and extending it on server side. Are you sure about this logic?? It usually will be a pojo/dto/model on the client/shared side implements IsSerializable and it is sent to the server. Then servers do the manipulation and returns it back.

Answer 3

It should implement the Serializable interface. You don't 'inherit' the implementation by extending the class.