无涯教程-Java 数据访问模式数据访问对象模式或DAO模式用于将底层数据访问API或操作与高层业务服务分开。以下是数

数据访问对象模式或DAO模式用于将底层数据访问API或操作与高层业务服务分开。以下是数据访问对象模式的参与者。

数据访问对象接口 - 此接口定义要在模型对象上执行的标准操作。
数据访问对象具体类 - 此类实现上述接口。此类负责从可以是数据库/ xml或任何其他存储机制的数据源获取数据。
模型对象或值对象 - 此对象是简单的POJO，其中包含用于存储使用DAO类检索到的数据的get/set方法。

数据访问对象模式实例

无涯教程将创建一个充当模型或值对象的 Student 对象。 StudentDao 是数据访问对象接口。 StudentDaoImpl 是实现数据的具体类访问对象接口。演示类 DaoPatternDemo 将使用 StudentDao 演示数据访问对象模式的使用。

第1步 - 创建Student对象。

Student.java

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;
}
}

第2步 - 创建数据访问Student对象接口。

StudentDao.java

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);
}

第3步 - 创建实现StudentDao接口的具体类。

StudentDaoImpl.java

import java.util.ArrayList;
import java.util.List;
public class StudentDaoImpl implements StudentDao {
//list is working as a database
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");
}
//retrive list of students from the database
@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");
}
}

第4步 - 使用 StudentDao 演示数据访问对象模式的用法。

DaoPatternDemo.java

public class DaoPatternDemo {
   public static void main(String[] args) {
      StudentDao studentDao = new StudentDaoImpl();
  </span><span class="com">//打印所有学生信息</span><span class="pln">
  </span><span class="kwd">for</span><span class="pln"> </span><span class="pun">(</span><span class="typ">Student</span><span class="pln"> student </span><span class="pun">:</span><span class="pln"> studentDao</span><span class="pun">.</span><span class="pln">getAllStudents</span><span class="pun">())</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
     </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"Student: [RollNo : "</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> student</span><span class="pun">.</span><span class="pln">getRollNo</span><span class="pun">()</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> </span><span class="str">", Name : "</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> student</span><span class="pun">.</span><span class="pln">getName</span><span class="pun">()</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> </span><span class="str">" ]"</span><span class="pun">);</span><span class="pln">
  </span><span class="pun">}</span><span class="pln">


  </span><span class="com">//更新学生信息</span><span class="pln">
  </span><span class="typ">Student</span><span class="pln"> student </span><span class="pun">=</span><span class="pln">studentDao</span><span class="pun">.</span><span class="pln">getAllStudents</span><span class="pun">().</span><span class="kwd">get</span><span class="pun">(</span><span class="lit">0</span><span class="pun">);</span><span class="pln">
  student</span><span class="pun">.</span><span class="pln">setName</span><span class="pun">(</span><span class="str">"Michael"</span><span class="pun">);</span><span class="pln">
  studentDao</span><span class="pun">.</span><span class="pln">updateStudent</span><span class="pun">(</span><span class="pln">student</span><span class="pun">);</span><span class="pln">

  </span><span class="com">//获取指定id学生信息</span><span class="pln">
  studentDao</span><span class="pun">.</span><span class="pln">getStudent</span><span class="pun">(</span><span class="lit">0</span><span class="pun">);</span><span class="pln">
  </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"Student: [RollNo : "</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> student</span><span class="pun">.</span><span class="pln">getRollNo</span><span class="pun">()</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> </span><span class="str">", Name : "</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> student</span><span class="pun">.</span><span class="pln">getName</span><span class="pun">()</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> </span><span class="str">" ]"</span><span class="pun">);</span><span class="pln">		

}
}

第5步 - 验证输出。

Student: [RollNo : 0, Name : Robert ]
Student: [RollNo : 1, Name : John ]
Student: Roll No 0, updated in the database
Student: [RollNo : 0, Name : Michael ]

无涯教程-Java 数据访问模式

数据访问对象模式实例

参考链接