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[] args) {        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