03.设计模式_抽象工厂模式(Abstract Fcatory)

抽象工厂模式：创建一些列相关或者互相依赖的对象的接口，而无需指定他们具体的类，

1、创建工厂Factory：

package patterns.design.factory;

import java.io.InputStream;
import java.util.Properties;

public class DaoFactory {

// 单例
private DaoFactory(){

try {
// 读配置文件获得实现类 类名
Properties props = new Properties();
InputStream in = DaoFactory.class.getClassLoader()
.getResourceAsStream("dao.properties");
props.load(in);

this.employeeDaoClassname = props.getProperty("employeeDaoClassname");

} catch (Exception e) {
throw new ExceptionInInitializerError(e);
}

}

private static DaoFactory instance = new DaoFactory();

public static DaoFactory newDaoFactory() {
return instance;
}

private String employeeDaoClassname;

// 提供方法返回实例对象dao
public EmployeeDao newEmplyeeDao() {
try {
// 反射创建对象
EmployeeDao employeeDao = (EmployeeDao) Class.forName(
this.employeeDaoClassname).newInstance();
return employeeDao;
} catch (Exception e) {
throw new RuntimeException(e);
}
}

}

2.在service中调用工厂类创建对象

package patterns.design.factory;

import java.util.List;

public class BusinessService {

// service 的方法取决于功能
private EmployeeDao employeeDao;

public BusinessService() {
// 自己创建对象
// 调用 工厂类获得一个dao对象
this.employeeDao = DaoFactory.newDaoFactory().newEmplyeeDao();
}

//查看所有员工
public List getAllEmployees() {
return employeeDao.getAll();
}

}

3.dao.properties

employeeDaoClassname=patterns.design.factory.EmployeeDaoImpl

4.EmployeeDao.java

package patterns.design.factory;
import java.util.List;
public interface EmployeeDao {
public List getAll();
}