设计模式学习—数据访问对象模式(Data Access Object Design Pattern)

一、我的理解

该模式是将其他形式表现的数据实体（比如存在数据库中的表）转换成编程可用的数据对象的形式。把低级的数据访问 API 或操作从高级的业务服务中分离出来。

二、实现方式

数据访问对象对外提供接口共高级业务获取数据对象，然后底层利用相关技术实现该接口。

三、实例

Java实例
Student类：转换后的数据对象类

package com.study.dp.dao;

public class Student {

private String name;
private int rollNo;

public Student(String name, int rollNo) {
super();
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;
}

}

StudentDao类：数据访问接口，供高级业务调用数据
package com.study.dp.dao;

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);

}
StudentDaoImpl类：具体实现方式
package com.study.dp.dao;

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

public class StudentDaoImpl implements StudentDao {

// 列表当做数据库
List<Student> students;

public StudentDaoImpl() {
students = new ArrayList<>();
Student student1 = new Student("Robert", 0);
Student student2 = new Student("John", 1);
students.add(student1);
students.add(student2);
}

@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");

}

@Override
public void deleteStudent(Student student) {
students.remove(student.getRollNo());
System.out.println("Student: Roll No "+student.getRollNo()+", deleted from database");
}

}
Demo类：测试用类
package com.study.dp.dao;

public class Demo {

public static void main(String[] arg
4000
s) {
StudentDao studentDao = new StudentDaoImpl();

// 输出所有学生
for (Student student : studentDao.getAllStudents()) {
System.out.println("Student: [RollNo : " + student.getRollNo() + ", Name : " + student.getName() + " ]");
}

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

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

}

四、应用场景