java设计模式之数据访问对象模式

客官°小女子只卖身不卖艺 2022-12-23 07:03 193阅读 0赞

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操作从高级的业务服务中分离出来。一下是数据访问对象模式的参与者。

*  数据访问对象接口(Data Access Object Interface)-该接口定义了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来检索到的数据。

**实现：**

创建一个作为模型对象的Student对象。StudentDao是数据访问对象接口。StudentDaoImpl是实现了数据访问对象接口的实体类。DaoPatternDemo类演示使用StudentDao来演示数据访问对象模式的用法。

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**创建数值对象：**

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;
        }
    }

**创建数据访问对象接口：**

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);
    }

**实现访问对象接口的实体类：**

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

**演示数据访问对象模式的用法：**

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

**执行程序，输出结果：**

student:[rollNo:0,name:Robert]
    student:[rollNo:1,name:john]
    Student: Roll No 0, updated in the database
    Student: [RollNo : 0, Name : michael ]

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