java - DAO的优缺点取决于DAOFactory

最近，我遇到了DAO具有DAOFactory实例的代码。和DAOFactory具有连接。 DAO使用DAOFactory的Connection进行操作。基本上，DAO依赖于DAOFactory。这是代码：

DAOFactory.java：

public abstract class DAOFactory {
   public static final int SQL_SERVER = 1;
   public static final int MY_SQL = 2;
   private Connection connection = null;

   public static DAOFactory getDAOFactory(int daoFactoryType) {
      DAOFactory daoFactory = null;

      switch (daoFactoryType) {
         case SQL_SERVER:
            daoFactory = new SQLServerDAOFactory();
            break;
         case MY_SQL:
            daoFactory = new MySQLDAOFactory();
            break;
      }

      return daoFactory;
   }

   public Connection getConnection() {
      return connection;
   }
   public void setConnection(Connection connection) {
      this.connection = connection;
   }

   public abstract UserDAO getUserDAO();
   ...
}

BaseDAO.java：

public abstract class BaseDAO {
   protected DAOFactory daoFactory;

   public BaseDAO(DAOFactory daoFactory) {
      this.daoFactory = daoFactory;
   }
}

UserDAO.java：

public interface UserDAO {
   public User getUserById(int userId) throws DAOException;
   ...
}

SQLServerUserDAO.java：

public class SQLServerUserDAO extends BaseDAO implements UserDAO {
   public SQLServerUserDAO (DAOFactory daoFactory) {
      super(daoFactory);
   }

   @Override
   public User getUserById(int userId) throws DAOException {
      // it uses the connection this way: this.daoFactory.getConnection();
      // implementation
   }
}

SQLServerDAOFactory.java：

public final class SQLServerDAOFactory extends DAOFactory {
   @Override
   public UserDAO getUserDAO() {
      UserDAO userDAO = null;

      userDAO = new SQLServerUserDAO(this);
      return userDAO;
   }
}

我通常会看到DAO具有Connection，但此对象却具有DAOFactory。

与具有Connection的DAO相比，使用具有DAOFactory的DAO的这种方法的优缺点是什么？

最佳答案

具有DAOFactory的DAO意味着更改工厂中的连接将更改由此创建的每个dao中的连接。这允许在知道连接实例之前创建DAO。

它的缺点是在DAOFactory和DAO之间创建循环依赖关系，并导致DAO具有比其所需更多的依赖关系，这会增加代码的复杂性。