JAVA - 工厂模式

1. 简单工厂违背OCP（Open Close Principle）原则 , 即对增加开放，对修改关闭。如果要符合OCP原则，要针对接口编程。

 //简单工厂模式，违反了OCP原则
 public class DAOFactory {

     public static IAddressDao getAddressDao() {
         return new AddressDao();
     }

     public static IUserDao getUserDao() {
         return new UserDao();
     }

 }

2.下一种模式的工厂进一步优化了简单工厂，但有一个缺点就是依赖于工厂的实现类

 public interface IFactoryDao {
     public IUserDao createUserDao();
     public IAddressDao createAddressDao();
 }

 public class MysqlDaoFactory implements IFactoryDao {
     private static IFactoryDao factory = new MysqlDaoFactory();
     private MysqlDaoFactory() {    }

     public static IFactoryDao getInstance() {
         return factory;
     }

     @Override
     public IAddressDao createAddressDao() {
         return new AddressDao();
     }

     @Override
     public IUserDao createUserDao() {
         return new UserDao();
     }
 }

 public class OracleDaoFactory implements IFactoryDao {
     private static IFactoryDao f = new OracleDaoFactory();
     private OracleDaoFactory(){}

     public static IFactoryDao getInstance() {
         return f;
     }
     @Override
     public IUserDao createUserDao() {
         return new UserOracleDao();
     }

     @Override
     public IAddressDao createAddressDao() {
         return new AddressOracleDao();
     }

 }

3.为了解决第二种工厂模式的弊端，需要使用配置文件，然后通过反射获取工厂实例

dao.properties 配置文件

factory=dawang.dao.MysqlDaoFactory

 package dawang.util;

 import dawang.dao.IFactoryDao;

 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
 import java.util.Properties;

 public class DaoUtil {
     public static void main(String[] args) {
         System.out.println(createDaoFactory());
     }
     @SuppressWarnings({ "rawtypes", "unchecked" })
     public static IFactoryDao createDaoFactory() {
         IFactoryDao f = null;
         try {
             Properties prop = PropertiesUtil.getDaoProp();
             String fs = prop.getProperty("factory");
             Class clz = Class.forName(fs);
             String mn = "getInstance";
             Method m = clz.getMethod(mn);
             f = (IFactoryDao)m.invoke(clz);
         } catch (ClassNotFoundException e) {
             e.printStackTrace();
         } catch (SecurityException e) {
             e.printStackTrace();
         } catch (NoSuchMethodException e) {
             e.printStackTrace();
         } catch (IllegalArgumentException e) {
             e.printStackTrace();
         } catch (IllegalAccessException e) {
             e.printStackTrace();
         } catch (InvocationTargetException e) {
             e.printStackTrace();
         }
         return f;
     }
 }