古诗MySQL数据库中使用到的DAO模式

一.什么是DAO模式

　　DAO(Data Access Object Pattern)用于将低层的数据操作API与上层的业务逻辑层分离，其主要涉及以下几个部分：

1.Data Access Object Interface

定义了在model object上的标准操作接口。

2.Data Access Object concrete class

实现了1中的接口，负责从database或者xml等中操作数据。

3.Model Object or Value Object

简单的POJO对象。

二.DAO模式例子
Model or Value Object :Student

Data Access Object Interface: StudentDAO

Concrete class Implement Data Access Object Interface:StudentDaoImpl

StudentDAO用来展示如何使用DAO模式。



Step1

Student.java

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

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

public String getName() {
return name;
}

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

public int getRollNo() {
return rollNo;
}

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

Step2

Data Access object interface

StudentDao.java

import java.util.List;

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

Step3

concrete class implemting above interface

StudentDaoImpl.java

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

public class StudentDaoImpl implements StudentDao {

//list is working as a database
List<Student> students;

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

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

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

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

step4

use StudentDao to demonstrate DAO pettern

public class DaoPatternDemo {
public 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() + " ]");
}
}