数据访问对象模式

1.数据访问对象模式简介

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。以下是数
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。

2.示例Demo

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

interface StudentDao {
    List<Student> getAllStudents();
    void deleteStudent(int number);
    void updateStudent(int number, String name);
    void addStudent(Student student);
}

class StudentDaoImpl implements StudentDao {
    private List<Student> lists = new ArrayList<Student>();

    public List<Student> getAllStudents() {
        return lists;
    }
    public void deleteStudent(int number) {
        for (Student stu : lists) {
            if (stu.getNumber() == number) {
                /*注意java中删除链表中元素是remove而不是delete*/
                lists.remove(stu);
                System.out.println("Delete student: name = " + stu.getName() + " number = " + stu.getNumber());
            }
        }
    }
    public void updateStudent(int number, String name) {
        for (Student stu : lists) {
            if (stu.getNumber() == number) {
                /*注意换行时“+”要写在一行的最前面而不是上一行的后面，不能使用连接符"\"*/
                System.out.println("Update student from: name = " + stu.getName() + " number = " + stu.getNumber()
                    + "  to: name = " + name + " number = " + number);
                stu.setName(name);
            }
        }
    }
    public void addStudent(Student student) {
        lists.add(student);
        System.out.println("Add student: name = " + student.getName() + " number = " + student.getNumber());
    }
}

class Student {
    private String name;
    private int number;

    public Student(String name, int number) {
        this.name = name;
        this.number = number;
    }

    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }

    public int getNumber() {
        return number;
    }
    public void setNumber(int number) {
        this.number = number;
    }
}

public class DaoPatternDemo {
    public static void main(String args[]) {
        StudentDao dao = createStudentDao();
        dao.updateStudent(2, "kitty");

        System.out.println("All students are:");
        for (Student stu : dao.getAllStudents()) {
            System.out.println("name = " + stu.getName() + " number = " + stu.getNumber());
        }
    }

    public static StudentDao createStudentDao() {
        StudentDao dao = new StudentDaoImpl();
        dao.addStudent(new Student("James", 1));
        dao.addStudent(new Student("jane", 2));
        dao.addStudent(new Student("lucy", 3));
        return dao;
    }
}