Very strange conversion behavior in JSF application

Today I've noticed a very strange conversion behavior in my JSF application. Please have a look at this:

I have this CRUD base class that is intended to be extended开发者_开发知识库 by some concrete managed bean classes:

public abstract class Cadastro<T, C extends Number> implements Serializable
{
    // _chave is the primary key
    private C _chave;
    // more fields...

    public C getChave()
    {
        return _chave;
    }

    public void setChave(C chave)
    {
        _chave = chave;
        if (_chave != null)
        {
            // More about this below...
            System.out.println(_chave.getClass().getName());
        }
    }

    // more methods...
}

This is a concrete managed bean class that extends the previous class:

@ManagedBean
@ViewScoped
public class CadastroArquivos extends Cadastro<Arquivo, Short>
{
}

Note the Short type for the primary key.

In the page I have an input text component for the key with a Short converter attached to it:

<h:inputText value="#{cadastroArquivos.chave}">
    <f:converter converterId="javax.faces.Short" />
</h:inputText>

So, as you can see, in the java side the *_chave* field has type Short in the CadastroArquivos class and in the page side there's a Short converter that matches this type. But when the page is posted back to the server, the System.out.println above prints for the *_chave* class:

java.lang.Long

and not java.lang.Short. How can it be?

Also, if I change the CadastroArquivos class to this to force even more the right conversion:

@ManagedBean
@ViewScoped
public class CadastroArquivos extends Cadastro<Arquivo, Short>
{
    @Override
    public Short getChave()
    {
        return super.getChave();
    }

    @Override
    public void setChave(Short chave)
    {
        super.setChave(chave);
    }
}

I get a ClassCastException:

value="#{cadastroArquivos.chave}": java.lang.ClassCastException: java.lang.Long cannot be cast to java.lang.Short

But if I change the declaration of the Cadastro class to this (note the C doesn't extend Number anymore):

public abstract class Cadastro<T, C> implements Serializable

everything works fine, at the cost of making my application less type safe in the java side. Can someone explain to me what's going on and how I can solve this?

Thank you.

Marcos