數(shù)據(jù)訪問對象模式（Data Access Object Pattern）或 DAO 模式用于把低級的數(shù)據(jù)訪問 API 或操作從高級的業(yè)務服務中分離出來。以下是數(shù)據(jù)訪問對象模式的參與者。

    數(shù)據(jù)訪問對象接口（Data Access Object Interface） - 該接口定義了在一個模型對象上要執(zhí)行的標準操作。
    數(shù)據(jù)訪問對象實體類（Data Access Object concrete class） - 該類實現(xiàn)了上述的接口。該類負責從數(shù)據(jù)源獲取數(shù)據(jù)，數(shù)據(jù)源可以是數(shù)據(jù)庫，也可以是 xml，或者是其他的存儲機制。
    模型對象/數(shù)值對象（Model Object/Value Object） - 該對象是簡單的 POJO，包含了 get/set 方法來存儲通過使用 DAO 類檢索到的數(shù)據(jù)。

Student.java

public class Student { //創(chuàng)建數(shù)值對象
    
    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;
       }
    
}

StudentDao.java

import java.util.List;

public interface StudentDao { //創(chuàng)建數(shù)據(jù)訪問對象接口
    
    public List<Student> getAllStudents();
       public Student getStudent(int rollNo);
       public void updateStudent(Student student);
       public void deleteStudent(Student student);
    
}

StudentDaoImpl.java

import java.util.ArrayList;
import java.util.List;
 
public class StudentDaoImpl implements StudentDao {
   
   //列表是當作一個數(shù)據(jù)庫
   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("Student1: Roll No " + student.getRollNo()
         +", deleted from database");
   }
 
   //從數(shù)據(jù)庫中檢索學生名單
   @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("Student2: Roll No " + student.getRollNo()
         +", updated in the database");
   }
}

DaoPatternDemo.java

public class DaoPatternDemo { //使用 StudentDao 來演示數(shù)據(jù)訪問對象模式的用法
    
    public static void main(String[] args) {
        StudentDao studentDao = new StudentDaoImpl();
        //輸出所有的學生
        for (Student student : studentDao.getAllStudents()) {
            System.out.println("Student3: [RollNo : "
                    +student.getRollNo()+", Name : "+student.getName()+" ]");
        }
        
        //更新學生
        Student student = studentDao.getAllStudents().get(0);
        student.setName("Walker");
        studentDao.updateStudent(student);
        
        //獲取學生
        studentDao.getStudent(0);
        System.out.println("Student4: [RollNo : "
                 +student.getRollNo()+", Name : "+student.getName()+" ]");  
    }
    
}