Re: Abstract Factory DAO Pattern in JSP Page

From:

Lew <lew@nowhere.com>

Newsgroups:

comp.lang.java.programmer

Date:

Fri, 26 Jan 2007 18:24:17 -0500

Message-ID:

<vb-dnd8ET6Y_ECfYnZ2dnUVZ_q-vnZ2d@comcast.com>

Dave wrote:

I *cannot* instantiate a DAOFactory object using <jsp:usebean..> because it
is an abstract class. I also *cannot* instantiate a PersonDAO object without
using the factory as it is an interface.

My initial thoughts are to use some sort of intermediate wrapper class that
instantiates the DAOFactory and handles requests. Is this the standard way
to handle this problem?

There are at least a couple of ways to handle this.

One way leverages the MVC pattern, whereby the logic class associated with the
screen places key objects into the request via setAttribute():

import entity.Person;
public class PersonalInfoHandler extends AbstractHandler
{
    private final PersonDao dao = (new DaoFactory()).getPersonDao();

    @Override
    public void handle()
    {
       Person person = dao.getPerson( request.getParameter( "person" ));
       request.setAttribute( "person", person );
    )
}

The dispatch servlet calls the handle() method (through an AbstractHandler
instance), which in turn places the found Person into the request attributes.
(Error checking omitted for simplicity.)

In the associated JSP one can use expressions like:

      <p>Person name: ${person.name}</p>

- Lew