The data access object in a computer software which is as an object which is responsible for providing abstract interface for communication to a specific form of database. Through the method of mapping, the app is able to call the persistence layer and the DAO then provides a certain type of data operations. You don’t need to expose what the database actually contains. This segregation is able to support the Single responsibility principle. It splits the need for the app in terms of data access from how can these needs be fulfilled with certain database schema, DBMS, etc. These needs can be domain specific or data types which is the public interface of the data access object.
Spring 5 Design Pattern Book
Data Access Object Design Pattern
The data access object design pattern is applicable to a large number of programming languages along with the same number of types of software which have persistence needs and a large number of types of databases. It associates with the Java EE apps along with the relational databases.
The objects of data access are comparatively simple to use and it stands as a separation between the most important two parts of the app, which is able to but should not know about each other. This evolves independently and frequently. The alteration in the business logic tends to depend on DAO interface also the alteration to the persistence logic cannot affect the DAO clients. But, this is only until, the interface is correctly and firmly implemented. The remaining part of the app does not have access to the entire details of the storage. You don’t need to modify the entire app to implement an alteration to the persistence mechanism. You can only modify a part of DAO implementation to do so.
Sample Implementation
Let’s see the sample implementation of this design pattern.
Step 1: Let’s create a Value Object.
Employee.java
/**
*
*/
package com.doj.patterns.j2ee.dataaccessobject;
/**
* @author Dinesh.Rajput
*
*/
public class Employee {
private String name;
private int empNo;
public Employee(String name, int empNo) {
super();
this.name = name;
this.empNo = empNo;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getEmpNo() {
return empNo;
}
public void setEmpNo(int empNo) {
this.empNo = empNo;
}
}
Step 2: Let’s create Data Access Object Interface.
EmployeeDao.java
/**
*
*/
package com.doj.patterns.j2ee.dataaccessobject;
import java.util.List;
/**
* @author Dinesh.Rajput
*
*/
public interface EmployeeDao {
List getAllEmployees();
Employee getEmployee(int empNo);
void updateEmployee(Employee employee, int index);
void deleteEmployee(Employee employee);
}
Step 3: Let’s create concrete class implementing above interface.
EmployeeDaoImpl.java
/**
*
*/
package com.doj.patterns.j2ee.dataaccessobject;
import java.util.ArrayList;
import java.util.List;
/**
* @author Dinesh.Rajput
*
*/
public class EmployeeDaoImpl implements EmployeeDao {
List employees;
public EmployeeDaoImpl() {
super();
employees = new ArrayList<>();
Employee employee1 = new Employee("Dinesh",100);
Employee employee2 = new Employee("Arnav", 111);
employees.add(employee1);
employees.add(employee2);
}
@Override
public List getAllEmployees() {
return employees;
}
@Override
public Employee getEmployee(int empNo) {
return employees.get(empNo);
}
@Override
public void updateEmployee(Employee employee, int index) {
employees.get(index).setName(employee.getName());
System.out.println("Employee: Emp No " + employee.getEmpNo() + ", updated in the database");
}
@Override
public void deleteEmployee(Employee employee) {
employees.remove(employee.getEmpNo());
System.out.println("Employee: Emp No " + employee.getEmpNo() + ", deleted from database");
}
}
Step 4: Let’s create a demo class and use the EmployeeDao to demonstrate Data Access Object pattern usage.
DaoPatternDemo.java
/**
*
*/
package com.doj.patterns.j2ee.dataaccessobject;
/**
* @author Dinesh.Rajput
*
*/
public class DaoPatternDemo {
/**
* @param args
*/
public static void main(String[] args) {
EmployeeDao employeeDao = new EmployeeDaoImpl();
//print all Employees
for (Employee employee : employeeDao.getAllEmployees()) {
System.out.println("Employee: [Emp No : " + employee.getEmpNo() + ", Name : " + employee.getName() + " ]");
}
//update Employee
Employee employee = employeeDao.getAllEmployees().get(0);
employee.setName("Anamika");
employeeDao.updateEmployee(employee, 0);
//get the Employee
employeeDao.getEmployee(0);
System.out.println("Employee: [Emp No : " + employee.getEmpNo() + ", Name : " + employee.getName() + " ]");
}
}
Step 5: Let’s run this demo class and verify the output.
Employee: [Emp No : 100, Name : Dinesh ] Employee: [Emp No : 111, Name : Arnav ] Employee: Emp No 100, updated in the database Employee: [Emp No : 100, Name : Anamika ]
