数据访问对象模式或DAO模式用于将低级数据访问API或操作与高级业务服务分开.以下是数据访问对象模式的参与者.
数据访问对象接口 - 此接口定义要对模型对象执行的标准操作.
数据访问对象具体类 - 此类实现上述接口.此类负责从数据源获取数据,该数据源可以是database/xml或任何其他存储机制.
模型对象或值对象 - 这个对象是包含get/set方法的简单POJO,用于存储使用DAO类检索的数据.
我们将创建一个 Student 对象作为模型或值对象. StudentDao 是数据访问对象接口. StudentDaoImpl 是实现数据访问对象接口的具体类. DaoPatternDemo ,我们的演示类,将使用 StudentDao 来演示数据访问对象模式的使用.
创建值对象.
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; } }
创建数据访问对象接口.
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); }
创建实现上述接口的具体类.
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"); } }
使用 StudentDao 演示数据访问对象模式用法.
DaoPatternDemo.java
public class DaoPatternDemo { public static void main(String[] args) { StudentDao studentDao = new StudentDaoImpl(); //print all students for (Student student : studentDao.getAllStudents()) { System.out.println("Student: [RollNo : " + student.getRollNo() + ", Name : " + student.getName() + " ]"); } //update student Student student =studentDao.getAllStudents().get(0); student.setName("Michael"); studentDao.updateStudent(student); //get the student studentDao.getStudent(0); System.out.println("Student: [RollNo : " + student.getRollNo() + ", Name : " + student.getName() + " ]"); } }
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 ]