Dao example

Using JDBC in the Project (Project Architecture)
http://rajjdbc.blogspot.in/

Using JDBC in the Project (Project Architecture)
with DAO Design Pattern

What is Low Level Persistence Logic?
• Low Level means it is specific to one type of dependent persistence logic
• Persistence Logic: is responsible for accessing persistence Data
• If I’m using low level persistence logic in Business Logic (i.e High Level
Logic) so I can not connect to all the Back end servers.
• To avoid this problem we have to use another layer , keep the persistence
logic in a separate object, that object is nothing but a Data Access Object
(DAO).
•
• SO here DAO is a Design Pattern, Design Pattern which gives a solution for
a problem.
• (Example: I’m facing a problem, I will try to interact with a friend who is
already faced the problem because he will have ready made solution for
that problem, no need to waste my time to solve the problem, because
already ready made solution (design pattern) is available

What is Low Level Persistence Logic?

Introducing DAO
• When it comes into the project (enterprise
application) we need to concentrate in
optimizing the code, making the more
reusable, and also testable.
• The DAO is the most common pattern
implemented into the enterprise applications.

What is a Pattern?
• Pattern is a three part document that describes
the context (situation), reoccurring problem and
the best solution for the problem in the given
context (situation).
• The software patterns are categorized into
multiple type for convenience in learning and
applying.
• The design patterns is one of the category. This
lists the patterns describing the problems related
to design and development of the software
applications

THE DAO DESIGN PATTERN:
•
• As the title describes this is a design pattern
• Context (situation):
• We want to create enterprise Application with reasonable business logic having a requirement of accessing
multiple (variety) of datastore and /or found that may have a requirement of migrating from one type of data
store (database) to other. Easy to migrate between the different types of data stores. That is in my application I
want to connect to LDAP to take credentials, same application I want to connect to File Systems to accept login
details.
• Problem:
• We want to separate the low-level persistence (data access) logic from Business Logic. But this so this solution
leaves a problem that is how do you separate in a best way? Thus this solution we kept in a problem.
• Forces: (Why):
• We want to have a proper responsibility division that is:
• (a) improves the quality of the system.
• (b) reduces the cost and time for the development
• To enable unit testing, make the system more comfortable for testing.
• Easy to migrate between the different types of data stores.
• Solution:
• Implement the low-level persistence logic into a separate object, exposing the data access operations through
high-level API to the service layer.

What is DAO ?
• Ans: DAO is a design pattern that describes
separating the low-level persistence logic from
the business logic, implementing into a
separate (independent) object.
•
• Note: this special object introduced
implementing the DAO pattern is also refered
as a DAO i.e: Data Access Object

• From this discussion and the above
architecture we understand JDBC is used for
implementing the DAO in Java for accessing
the tabular data store

Use Case diagram of our project

Implementing DAO Design Pattern in
our project

Implementing the Data Access Layer for ‘CreateEmployee’ use
case of ‘Employee Management System (EMS).
• For Example:
• Implementing the Data Access Layer for ‘CreateEmployee’ use case of ‘Employee Management System (EMS).
•
• //EmployeeDAOI.java
• package com.st.ems.dao;
• public interface EmployeeDAOI
• {
• void save(int eno,String name, double sal, int dno);
• //we will change this struture later
• //we will add some more methods as we proceed
• }
•
•
• //EmployeeDAO.java
• package com.st.ems.dao.jdbc;
• import com.st.ems.dao.EmployeeDAOI;
• import java.sql.*;
• import java.util.*;
• public class EmployeeDAO implements EmployeeDAOI
• {
• public void save(int eno, String name,double sal, int dno)
• {
• //this method is responsible for saving the given details into emp table
• //to do: execute the following SQL
• String sql="insert into emp values("+eno+",'"+name+",',"+sal+","+dno+")";

• //how to execute?
• //use JDBC
• //Write this Connection con=null here only to make visible to all the blocks
• Connection con=null;//null is necessary whn u r declaring as a local variable
• try
• {
• //step 1.1
• String driverClassName="oracle.jdbc.driver.OracleDriver";//here we are using oracle driver
• Class c=Class.forName(driverClassName);
• Driver d=(Driver)c.newInstance();
• //step 1.2
• String jdbcUrl="jdbc:oracle:thin:@localhost:1521:XE";
• Properties p=new Properties();
• p.put("user","system");
• p.put("password","manager");
• //Connection con=null;//i can not use con ref variable in finally block as it is local to this
• block
•
•

• con=d.connect(jdbcUrl,p);
• //step2
• Statement st=con.createStatement();
• //step3
• st.executeUpdate(sql);
•
•
• }//end of try block
• catch(Exception e)
• {
• e.printStackTrace();
• //to report the error, we will set run time error
• throw new RuntimeException(e);
• }
• finally
• {
• try
• {
• //step 4:
• con.close();
•
• }//try
• catch(Exception e){}
• }//finally
•
•
• }//save
• }//class

• /* now we are writing Tese case for DAO object [that is save()] for this we have to use JUNIT but
• we are using main() for this application
• */
• //EmployeeDAOTestCase.java
• import com.st.ems.dao.jdbc.EmployeeDAO;
• import com.st.ems.dao.EmployeeDAOI;
•
•
• public class EmployeeDAOTestCase
• {
• private EmployeeDAOI edao;
• public void testsave()
• {
• edao.save(102,"e102",20000,20);
• System.out.println("Details saved");
• }
• public static void main(String s[])
• {
• EmployeeDAOTestCase test=new EmployeeDAOTestCase();
• test.edao=new EmployeeDAO();
• test.testsave();//here Driver object is created
• //test.testsave();//here 2nd Driver object is created but one Driver object is enought to handle
• //multiple request from diffrent clients, connections as it is a Thread -safe
• }
• }

• /*
• D:materialjava(E DRIVE)javaAdvJavajdbcDAO>javac
-d . *.java
• D:materialjava(E
DRIVE)javaAdvJavajdbcDAO>D:materialjava(E
• DRIVE)javaAdvJavajdbcDAO>set
classpath=C:oraclexeappor
• acleproduct10.2.0serverjdbclibojdbc14.jar;.;
• D:materialjava(E DRIVE)javaAdvJavajdbcDAO>java
EmployeeDAOTestCase
• Details saved
• */

Work flow of our program

Q: is our DAO created efficient?
• Ans: No, we need to multiple changes. Let us look into all of them
one after the other
• In the EmployeeDAO created earlier the save() method is
programmed to create a new instance (object) of Driver class on
every request, which is not effective.
• Considering the following points with respect to the Driver:
• The Driver object is Thread-safe means Driver object performs
consistently even on concurrent requests from multiple threads
• A single instance of Driver can be used to create multiple
connections because it is Thread-safe. If we create the multiple
instances of Driver class, unnecessarly garbage is stored into the
memory, and performance becomes slow.
• Considering these points a single instance of Driver is enough for an
application per data base.

• (INTRODUCTION TO DRIVER MANAGER)
• That means we want to redesign the DAO such that it should work with single instance of Driver class irrespective
of the number of clients and requests.
• To address this requirements JDBC introduces DriverManager class
• Q: What is Driver Manager class?
• The java.sql.DriverManager is a factory class that is designed to create the Connection Managing the Driver
objects.
• Why DriverManager?
• Ans: to centralize the code( means connect() method) creating the Connection using the Driver object. So that we
can avoid multiple instances (objects) of a Driver class to create. Here the code means connect() method.
•
• Q: How DriverManager functions?
• We know that the basic functionality of the DriverManager is to create the Connection managing the Driver
object. The getConnection() method will create connection using registered Driver object.
•
• Working with DriverManager
• Fig: DriverManager FactoryClass(.JPG
• The following two steps are involved in doing this:
• Step1: Register the Driver to DriverManager
• Step2: Invoke the getConnection() to get the Connection
•

Dao example

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