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

傷城~ 2022-06-09 13:47 175阅读 0赞

# 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 #

![Center][]

###### 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 #

[Center]: /images/20220609/97b9ded02a90489d96609c8b6775c9b3.png