Java设计模式 - 数据访问对象模式
数据访问对象模式或DAO模式将数据访问API与高级业务服务分离。
DAO模式通常具有以下接口和类。
数据访问对象接口定义模型对象的标准操作。
数据访问对象类实现以上接口。可能有多个实现，例如，一个用于数据库，一个用于文件。
模型对象简单的POJO包含get/set方法来存储数据。
例子
import java.util.ArrayList;
import java.util.List;
class Employee {
private String name;
private int id;
Employee(String name, int id) {
this.name = name;
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
}
interface EmployeeDao {
public List<Employee> getAll();
public Employee get(int id);
public void updateStudent(Employee student);
public void delete(Employee student);
}
class EmployeeDaoImpl implements EmployeeDao {
List<Employee> employeeList;
public EmployeeDaoImpl() {
employeeList = new ArrayList<Employee>();
Employee emp1 = new Employee("Jack", 0);
Employee emp2 = new Employee("Tom", 1);
employeeList.add(emp1);
employeeList.add(emp2);
}
@Override
public void delete(Employee student) {
employeeList.remove(student.getId());
System.out.println("Employee: No " + student.getId()
+ ", deleted from database");
}
@Override
public List<Employee> getAll() {
return employeeList;
}
@Override
public Employee get(int rollNo) {
return employeeList.get(rollNo);
}
@Override
public void updateStudent(Employee emp) {
employeeList.get(emp.getId()).setName(emp.getName());
System.out.println("Emp:No " + emp.getId()
+ ", updated in the database");
}
}
public class Main {
public static void main(String[] args) {
EmployeeDao empDao = new EmployeeDaoImpl();
for (Employee emp : empDao.getAll()) {
System.out.println("Emp: [No : " + emp.getId() + ", Name : "
+ emp.getName() + " ]");
}
Employee emp = empDao.getAll().get(0);
emp.setName("Jane");
empDao.updateStudent(emp);
empDao.get(0);
System.out.println("Emp: [No : " + emp.getId() + ", Name : "
+ emp.getName() + " ]");
}
}
上面的代码生成以下结果。
Emp:[NO:0,name:Jack]
Emp:[NO:1,name:Tom]
Emp:NO 0,updated in the database
Emp:[NO:0,name:Jane]