Data Access Object Pattern

Data Access Object Pattern or DAO pattern is used to separate low level data accessing API or operations from high level business services. Following are the participants in Data Access Object Pattern.

Data Access Object Interface - This interface defines the standard operations to be performed on a model object(s).

Data Access Object concrete class - This class implements above interface. This class is responsible to get data from a data source which can be database / xml or any other storage mechanism.

Model Object or Value Object - This object is simple POJO containing get/set methods to store data retrieved using DAO class.

Implementation

We are going to create a Student object acting as a Model or Value Object.StudentDao is Data Access Object Interface.StudentDaoImpl is concrete class implementing Data Access Object Interface. DaoPatternDemo, our demo class, will use StudentDao to demonstrate the use of Data Access Object pattern.

Step 1

Create Value Object.

Student.java

pubpc class Student {
   private String name;
   private int rollNo;

   Student(String name, int rollNo){
      this.name = name;
      this.rollNo = rollNo;
   }

   pubpc String getName() {
      return name;
   }

   pubpc void setName(String name) {
      this.name = name;
   }

   pubpc int getRollNo() {
      return rollNo;
   }

   pubpc void setRollNo(int rollNo) {
      this.rollNo = rollNo;
   }
}

Step 2

Create Data Access Object Interface.

StudentDao.java

import java.util.List;

pubpc interface StudentDao {
   pubpc List<Student> getAllStudents();
   pubpc Student getStudent(int rollNo);
   pubpc void updateStudent(Student student);
   pubpc void deleteStudent(Student student);
}

Step 3

Create concrete class implementing above interface.

StudentDaoImpl.java

import java.util.ArrayList;
import java.util.List;

pubpc class StudentDaoImpl implements StudentDao {
	
   //pst is working as a database
   List<Student> students;

   pubpc StudentDaoImpl(){
      students = new ArrayList<Student>();
      Student student1 = new Student("Robert",0);
      Student student2 = new Student("John",1);
      students.add(student1);
      students.add(student2);		
   }
   @Override
   pubpc void deleteStudent(Student student) {
      students.remove(student.getRollNo());
      System.out.println("Student: Roll No " + student.getRollNo() + ", deleted from database");
   }

   //retrive pst of students from the database
   @Override
   pubpc List<Student> getAllStudents() {
      return students;
   }

   @Override
   pubpc Student getStudent(int rollNo) {
      return students.get(rollNo);
   }

   @Override
   pubpc void updateStudent(Student student) {
      students.get(student.getRollNo()).setName(student.getName());
      System.out.println("Student: Roll No " + student.getRollNo() + ", updated in the database");
   }
}

Step 4

Use the StudentDao to demonstrate Data Access Object pattern usage.

DaoPatternDemo.java

pubpc class DaoPatternDemo {
   pubpc static void main(String[] args) {
      StudentDao studentDao = new StudentDaoImpl();

      //print all students
      for (Student student : studentDao.getAllStudents()) {
         System.out.println("Student: [RollNo : " + student.getRollNo() + ", Name : " + student.getName() + " ]");
      }


      //update student
      Student student =studentDao.getAllStudents().get(0);
      student.setName("Michael");
      studentDao.updateStudent(student);

      //get the student
      studentDao.getStudent(0);
      System.out.println("Student: [RollNo : " + student.getRollNo() + ", Name : " + student.getName() + " ]");		
   }
}

Step 5

Verify the output.

Student: [RollNo : 0, Name : Robert ]
Student: [RollNo : 1, Name : John ]
Student: Roll No 0, updated in the database
Student: [RollNo : 0, Name : Michael ]