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();
 }