RE: DAO design pattern -- JAVA400-L

Lim,

No worries.  Yes, JT400SomeObjectDAO needs to implement SomeObjectDAO.

There are a couple of reasons for a distinct DAO layer:

* Forces you to thing about and define the key persistance related 
operations early on (e.g., load/save/delete/findByXXX)
* Hides the implementation behind an interface, allowing you to change the 
implementation if required.
* Keeps data access code out of the GUI and other parts of your 
application.

SomeObjectDAOFactory is used to centralise the decision as to which 
concrete implementation of SomeObjectDAO should be created.  In simple 
applications it can be simply hard coded, otherwise use some method to 
determine the class at runtime (e.g., system properties, configuration 
files, or the Spring Framework)


   public void printSomeObject(Integer id) {

        SomeObjectDAO dao = SomeObjectDAOFactory.getInstance().getDAO();

        // you could make SomeObjectDAOFactory.getInstance() a static 
method
        // returning SomeObjectDAO to shorten the long lines.

        SomeObject object = dao.findByID(id);

        System.err.println(object.toString());

}

Regards,

Niall






"Lim Hock-Chai" <Lim.Hock-Chai@xxxxxxxxxxxxxxx> 
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04/01/2005 16:19
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RE: DAO design pattern






Please note that I'm a beginner java programmer.  So, here I go.

I'm assuming that JT400SomeObjectDAO needs to implement SomeObjectDAO.  Is 
that correct?

Still not sure what SomeObjectDAOFactory for yet. 


Here is a stupid beginner question:
Why do I need SomeObjectDAO interface if JT400SomeObjectDAO is probably 
the only class that will implement SomeObjectDAO? 

Can you or Collin give me a short info on how Ibatis or Hibernate help 
development cycle? 

-----Original Message-----
From: java400-l-bounces@xxxxxxxxxxxx
[mailto:java400-l-bounces@xxxxxxxxxxxx]On Behalf Of
Niall.Smart@xxxxxxxxxxxxxxx
Sent: Tuesday, January 04, 2005 4:59 AM
To: Java Programming on and around the iSeries / AS400
Cc: java400-l-bounces+niall.smart=friendsfirst.ie@xxxxxxxxxxxx; Java
Programming on and around the iSeries / AS400
Subject: Re: DAO design pattern


Lim

Create an interface which defines the data related operations 
independantly of any particular representation/access method (i.e., 
file/JDBC, etc)

public interface SomeObjectDAO {

        public void create(SomeObject object)
                throws DAOException;

        public void delete(Integer objectID)
                throws DAOException;

        public SomeObject findByID(Integer objectID)
                throws DAOException;

        public List findByKeyword(String keyword)
                throws DAOException;
}

Then write an implementation of this interface using the JT/400 API:

public class JT400SomeObjectDAO {

        public SomeObject findByID(Integer objectID) {
 
                AS400File file = ....

                SomeObject someObject = new someObject();

                someObject.setFoo(file.readInteger());
 
                return someObject;
        }

        // ...
}

And finally write a factory to create instances of SomeObjectDAO:

public class SomeObjectDAOFactory {

        private static instance = new SomeObjectDAOFactory();

        public static SomeObjectDAOFactory getInstance() {
                return instance;
        }

        public SomeObjectDAO newInstance() {
                return new JT400SomeObjectDAO();
        }

}

You don't gave to use checked exceptions.   A framework like spring can 
obviate the need for trivial factory objects.




"Lim Hock-Chai" <Lim.Hock-Chai@xxxxxxxxxxxxxxx> 
Sent by: java400-l-bounces+niall.smart=friendsfirst.ie@xxxxxxxxxxxx
03/01/2005 18:40
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DAO design pattern






Anybody has a good example on how should I design my web application for 
any file access related transaction?
 
I'm using struts to create this web apps.  I just wonder when I'm in the 
Action Form and I need to do some edit/insert/update on a record in a 
file, what is the correct way to design this.  I've read some article 
about DAO design pattern.  If this is a good approach, can anybody provide 

some example.  (Note: I'm using Tomcat4.1 and plan to use DBCP for 
connection pooling.) 
 
thanks.
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