Question

I followed https://developers.google.com/web-toolkit/articles/mvp-architecture .
In their model, they use one class ‘Contact’ and a light version of that class called ‘ContactDetails’.
Since I don’t really need a light version, I removed ContactDetails and replaced it by Contact.

Now I run into exceptions like

Type 'org.eclipse.persistence.indirection.IndirectList' was not included in the set of types which can be serialized by this SerializationPolicy or its Class object could not be loaded. For security purposes, this type will not be serialized.: instance = {IndirectList: not instantiated}

The reason is, as I found out here (http://stackoverflow.com/a/6778986/1141785), that the Contact class is a class which uses Persistence API techniques, which should not be sent to the wire.

So is the ContactDetails class my DTO class which should be sent through the wire?
Is there no way to avoid using this extra class?

The reason I want to avoid using the ‘light’ version is, that I want to edit the Contact class in a DataGrid using the FieldUpdater.

Do I have any advantages in my case when I use the DTO class?

How can I avoid that I have so many duplicated code in the Contact and ContactDetails classes, when they should by nearly the name?

Answer 1

When using JPA, you can have a class containing a List such as:

public class Contact implements IsSerializable {
    // ...
    private List<Address> addresses;
    // ...
}

But when Contact is created, addresses is set to an instance of IndirectList. This allows lazy loading of the collection from the database, but won’t work on the client. You would need to replace it with something like an ArrayList before sending it to the client. You can set it to an empty list, or copy the contents to a new list.

If the elements of the list contain collections themselves, then you need to replace these collections as well. You’d need to be careful about circular references and pulling too many items from the database.