深入理解面向接口编程：在类中调用接口的方法，而不必关心具体的实现。这将有利于代码的解耦。使程序有更好的可移植性和可扩展性
1）动态修改Customer的存储方式：通过修改类路径下的switch.properties文件的方式来实现
2）CustomerServlet中不能在通过private CustomerDAO customerDAO = new CustomerDAOXMLImpl();的方式来写死实现类
3）通过一个类的一个方法来获取具体的实现类对象
当前WEB应用启动的时候，InitServlet被创建，并由Servlet容器调用其init()方法：
1）读取类路径下的switch.properties文件
2）获取switch.properties的type属性值
3）赋给CustomerDAOFactory的type属性值
创建CustomerServlet时，为customerDAO属性赋值是通过CustomerDAOFactory的getCustomerDAO()方法完成的。
CustomerDAOFactory
public class CustomerDAOFactory {
private Map<String,CustomerDAO> daos = new HashMap<String,CustomerDAO>();
private CustomerDAOFactory(){
daos.put("jdbc",new CustomerDAOJdbcImpl());
daos.put("xml",new CustomerDAOXMLImpl());
}
private static CustomerDAOFactory instance = new CustomerDAOFactory();
public static CustomerDAOFactory getInstance(){
return instance;
}
private static String type = null;
public void setType(String type){
this.type = type;
}
public CustomerDAO getCustomerDAO(){
return daos.get(type);
}
}
转载于:https://www.cnblogs.com/yangHS/p/11150985.html
