Room Using Date field

Question

You're converting from Date to Long (wrapper) and from long (primitive) to Date. I changed it to Long and it compiled. Besides, unboxing null in your converter produces a NPE.

public class DateConverter {

    @TypeConverter
    public static Date toDate(Long dateLong){
        return dateLong == null ? null: new Date(dateLong);
    }

    @TypeConverter
    public static Long fromDate(Date date){
        return date == null ? null : date.getTime();
    }
}

See my complete example.

Refer to the documentation : https://developer.android.com/training/data-storage/room/referencing-data

public class Converters {
    @TypeConverter
    public static Date fromTimestamp(Long value) {
        return value == null ? null : new Date(value);
    }

    @TypeConverter
    public static Long dateToTimestamp(Date date) {
        return date == null ? null : date.getTime();
    }
}

Then map it to the database.

@Database(entities = {User.class}, version = 1)
@TypeConverters({Converters.class})
public abstract class AppDatabase extends RoomDatabase {
    public abstract UserDao userDao();
}

And the entity.

@Entity
public class User {
    private Date birthday;
}

I had this same problem (how to store time to Room), but I was using Calendar, so I made this: [note: This anwer is for Calendar ; the main reason is that Calendar is now supported]

edit: the main reason for this answer is that Date is deprecated, so here you go

  @TypeConverter
  public static Calendar toCalendar(Long l) {
    Calendar c = Calendar.getInstance();
    c.setTimeInMillis(l);
    return c;
  }

  @TypeConverter
  public static Long fromCalendar(Calendar c){
    return c == null ? null : c.getTime().getTime();
  }

Put converter class in class of data base, not in the model :

@Database(entities = {
    Patient.class,Medicine.class,Tooth.class,})

@TypeConverters({TimeConverter.class,OutBoundConverter.class})

public abstract class PatientDataBase extends RoomDatabase {//your data base}

AndroidThreeTen is the port of Java8 new time classes, which unfortunately are available only for api>=26. Using https://github.com/JakeWharton/ThreeTenABP , we can use LocalDateTime on all versions of Android. Here in kotlin the converter,

class Converters {
    @TypeConverter
    fun fromTimestamp(value: Long?): LocalDateTime? {
        return value?.let {
            LocalDateTime.ofInstant(
                Instant.ofEpochMilli(it), ZoneId.systemDefault()
            )
        }
    }

    @TypeConverter
    fun LocalDateTimeToTimestamp(date: LocalDateTime?): Long? {
        return date?.atZone(ZoneId.systemDefault())?.toInstant()?.toEpochMilli()
    }
}

which, as other good answers already said, it's declared on the Database abstract class:

@Database(entities = {User.class}, version = 1)
@TypeConverters({Converters.class})
public abstract class AppDatabase extends RoomDatabase {
    public abstract UserDao userDao();
}