Scott Evans wrote:
> Craig and Kevin,
>
> First of all, thanks - I'm a newbie and I've really learned a lot from
> reading your correspondence.
>
> I'm dying to know, the instance of the action class, is it multithreaded or
> do you use it to create other instances of the same class?
>
In my implementation, the Action class implementation is required to be
multithreaded, because I create only one instance of each Action class (the first
time it is called). Mostly, that just means avoiding instance variables in the
action classes -- IMHO bean classes you access within an action class should be
responsible for providing any required synchronization when possible race
conditions can occur.
>
> As well, what happens with input errors? More methods in the Action
> interface, like:
>
Again, this is my approach ... others will be different. My "Action" interface
looks like this:
public interface Action {
public void perform(HttpServlet servlet,
HttpServletRequest request,
HttpServletResponse response)
throws IOException, ServletException;
}
The similarity to the calling signature for doGet() and doPost() is very
deliberate. In essence, an Action class's perform() method can do anything that a
servlet's doGet() method can do. For example, in the case of an input error, my
Action class does a RequestDispatcher.forward() back to the JSP page with the
input form on it. I keep a session-scope bean with all of the input values that
the user last entered, which I use in the JSP page to show the page exactly as it
was input (plus an error message).
So, an action class might look like this:
public class SaveCustomerAction implements Action {
// NOTE -- No instance variables because of multithreaded access!
public void perform(HttpServlet servlet,
HttpServletRequest request, HttpServletResponse response)
throws IOException, ServletException {
... update the session bean with all the user's input values ...
if (...there is an input error ...) {
... store an error message bean as a request attribute ...
RequestDispatcher rd =
servlet.getServletContext().getRequestDispatcher("/enterCustomer.jsp");
rd.forward(request, response);
return;
}
ConnectionPool pool = getServletContext().getAttribute("pool");
Connection conn = pool.allocateConnection(); // Connection pool is an
application scope bean
... save the customer in the database ...
conn.close(); // Causes the connection to be returned to the pool
RequestDispatcher rd =
servlet.getServletContext().getRequestDispatcher("/nextMenu.jsp"); //
Or wherever
rd.forward(request, response);
return;
}
}
As an aside, you can see above why I pass the servlet argument -- so that I can
access anything available through the servlet. I can even log messages by calling
servlet.log(), or whatever else is necessary.
> thanks again,
>
> Scott
>
Craig McClanahan
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