Struts Tutorials:
Struts2 Tag CheckBoxList
, Checkbox, Iterator, IF
Struts2 Tag Library Example
Struts2 Tiles Example
Struts2 Tiles I18N Example
Struts2 Questions
Struts Tiles I18N Example
Struts Eclipse MVC
Struts2 Tags
Struts2 Example and Tutorial
Struts MVC
Struts2 Validation



Hibernate Tutorials:
Hibernate Case Study
Class Hierarchy Persist Example
Using Hibernate Interceptor
Hibernate Questions with Answer
Hibernate Many-to-Many Mapping Example
Hibernate one-to-many Mapping Example
Hibernate and ORM tools
Spring Hibernate Example
Hibernate SessionFactory Example
Hibernate Mapping Class Hierarchy
Hibernate Questions
Hibernate SessionFactory Questions

Spring Hibernate Example:
Spring Hibernate Case Study

Written By : ISHTEK
Title :
DAO Data Access Object

Description :
Advantages Discussed
More...

Written By : ISHTEK
Title :
Business Delegate

Description :
Advantages or Benefits discussed
More...

Tags/Keywords : Data Access Object, DAO, Data, Access, Object, J2EE Design Patterns, Example, Code, Tutorial, Article
Author : Amit
Date (Year/Month/Date): 2009-01-25
Data Access Object - A J2EE Design Pattern explained with an example

Please be informed that NONE of the design/code from this
page is claiming to be some sort of best practices and we DO NOT expect
any of our visitor/reader of this page to assume this as some sort of
best practice for any context and should not be using this 
as it is without appropriate evaluation to their, so to say, 
specific programming context.

This page intends only to provide bit and piece of known ways  for
doing some sort of example and may not be fit for any other purpose.




Advertisement : 


DAO - Data Access Object - A J2EE Design Pattern to
isolate client/user from Persistence API, thus making
no change in client code, in case there are changes
in storage or persistence implementation.

How to design application so as to achieve this
functionality of DAO?

Let us explore this possibility by a sample case
study.

Our objective is to make client code (user of database/
persistence API), compilation free, in case there is
a major change in storage/database/ persistence API
(such as ORM-Object Relational Mapping tools).
Please write your suggestions / comments on this Page.

I can remember a Java design Pattern - Factory pattern that returns
different implementation of an Interface, based on some input parameter.
So we shall use Factory design pattern as an interfacing between Client
code (it can be business service, POJO or Servlet code etc.) and
persistence layer (it can be JDBC, Hibernate, iBatis, or any other ORM
implementations).

Factory Pattern requires at least two major parts, one is an interface
and other is an abstract class.

We define this interface as follows:

1. EmployeeDAO.java
-------------------------------------------------------------------------
public interface EmployeeDAO
{
 public void findEmployee(int id) throws DatabaseException;
 public void deleteEmployee(int id) throws DatabaseException;
 public Employee saveEmployee(Employee employee) throws DatabaseException;
 public Employee updateEmployee(Employee employee) throws DatabaseException;
 ....
 ....
}
-------------------------------------------------------------------------

2. An abstract class as follows:
 DAOFactory.java
-------------------------------------------------------------------------
public abstract class DAOFactory
{
 static int HIBERNATE_DAO_FACTORY = 1;
 protected DAOFactory()
 {

 }
 public static DAOFactory getInstance(int n)
 {
   if(n == HIBERNATE_DAO_FACTORY)
     return new HibernateDAOFactory();
   else
     return null;
   }
 public abstract EmployeeDAO getEmployeeDAO();
 .....
 .....
}
-------------------------------------------------------------------------

And a constants Java interface as follows:

3. Constants.java
-------------------------------------------------------------------------
public interface Constants
{
	int DAO_INDENTIFIER = 0; //For Hibernate as ORM Tool for this Application
	....
}
-------------------------------------------------------------------------


Major parts/classes from users/client perspective is as follows:


Those parts, that are ticked in this above class diagram (Created using ArgoUML)
are prone to change, in case there is a change in persistence implementation,
like from Hibernate to JDBC, or from JDBC to iBatis and if there is any
change in business methods like findEmployee to locateEmployee etc.

Implementation of the specific Factory implementation like factory for Hibernate
, factory for iBatik etc are left to the visitor/reader of this writing as an
exercise. We shall be discussing this in coming articles/writing.
If interested, you can reply/write your ideas of implementing this Factory
implementation for Hibernate.

Thanks.



Advertisement : 



Author of this article/writeup has expressed his/her willingness
to help or guide users with any technical difficulties he/she faces
while working with the example code environment setting up, running
and resolving any such exception raised during compile or at runtime.
You may ask for any technical doubt or seek technical help related to
this article by using following form to reach for technical help
from the Author for FREE.

This article's Author shall be reading your request and responding
within reasonable time (no resolution timeframe defined as such).

Copyright © 2008-2009, Interview-Questions-Tips-Forum, All Rights Reserved.