数据访问对象模式(Data Access Object Pattern)或 DAO 模式用于把低级的数据访问 API 或操作从高级的业务服务中分离出来
数据访问模式涉及到的参与者有:
- 数据访问对象接口(Data Access Object Interface) - 该接口定义了在一个模型对象上要执行的标准操作
- 数据访问对象实体类(Data Access Object concrete class) - 该类实现了上述的接口。该类负责从数据源获取数据,数据源可以是数据库,也可以是 xml,或者是其他的存储机制
- 模型对象/数值对象(Model Object/Value Object) - 该对象是简单的 POJO,包含了 get/set 方法来存储通过使用 DAO 类检索到的数据
实现
1、 创建一个作为模型对象或数值对象的Student对象;
2、 定义StudentDao作为数据访问对象接口;
3、 定义StudentDaoImpl实现了数据访问对象接口的实体类;
4、 定义DaoPatternDemo使用StudentDao来演示数据访问对象模式的用法;
范例
1. 创建数值对象
Student.java
// author: DDKK.COM 弟弟快看,程序员编程资料站(ddkk.com)
// Copyright © 2015-2065 ddkk.com. All rights reserved.
package com.ddkk.gof;
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;
}
}
2. 创建数据访问对象接口
StudentDao.java
// author: DDKK.COM 弟弟快看,程序员编程资料站(ddkk.com)
// Copyright © 2015-2065 ddkk.com. All rights reserved.
package com.ddkk.gof;
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);
}
3. 创建实现了上述接口的实体类
StudentDaoImpl.java
// author: DDKK.COM 弟弟快看,程序员编程资料站(ddkk.com)
// Copyright © 2015-2065 ddkk.com. All rights reserved.
package com.ddkk.gof;
import java.util.ArrayList;
import java.util.List;
public class StudentDaoImpl implements StudentDao {
//列表是当作一个数据库
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");
}
//从数据库中检索学生名单
@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");
}
}
4. 使用 StudentDao 来演示数据访问对象模式的用法
CompositeEntityPatternDemo.java
// author: DDKK.COM 弟弟快看,程序员编程资料站(ddkk.com)
// Copyright © 2015-2065 ddkk.com. All rights reserved.
package com.ddkk.gof;
public class DaoPatternDemo {
public static void main(String[] args) {
StudentDao studentDao = new StudentDaoImpl();
//输出所有的学生
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()+" ]");
}
}
编译运行以上范例,输出结果如下
$ javac -d . src/main/com.ddkk/gof/DaoPatternDemo.java
$ java com.ddkk.gof.DaoPatternDemo
Student: [RollNo : 0, Name : Robert ]
Student: [RollNo : 1, Name : John ]
Student: Roll No 0, updated in the database
Student: [RollNo : 0, Name : Michael ]