我怎样才能在不重复的情况下重写这些方法？答案

【问题标题】：How can i rewrite this methods without duplication?我怎样才能在不重复的情况下重写这些方法？
【发布时间】：2018-02-20 07:31:51
【问题描述】：

怎样才能使这段代码不重复？这种方法类似。

创建电话号码的方法：

   private List<String> createPhoneNumbers(String sqlStatement, Long id) {
        List<String> phones = new ArrayList<>();
        try (PreparedStatement statement = this.connection.prepareStatement(sqlStatement)) {
            statement.setLong(1, id);
            try (ResultSet resultSet = statement.executeQuery()) {
                while (resultSet.next()) {
                    phones.add(resultSet.getString("phoneNumber"));
                }
                return phones;
            }
        } catch (SQLException e) {
            e.printStackTrace();
            return null;
        }
    }

创建好友列表的方法：

   private List<Account> createFriendList(String sqlStatement, Long id) {
        List<Account> friends = new ArrayList<>();
        try (PreparedStatement statement = this.connection.prepareStatement(sqlStatement)) {
            statement.setLong(1, id);
            try (ResultSet resultSet = statement.executeQuery()) {
                while (resultSet.next()) {
                    friends.add(createSimpleElement(resultSet));
                }
                return friends;
            }
        } catch (SQLException e) {
            e.printStackTrace();
            return null;
        }
    }

创建组列表的方法：

   private List<Group> createGroupList(String sqlStatement, Long id) {
        List<Group> groups = new ArrayList<>();
        try (PreparedStatement statement = this.connection.prepareStatement(sqlStatement)) {
            statement.setLong(1, id);
            try (ResultSet resultSet = statement.executeQuery()) {
                while (resultSet.next()) {
                    groups.add(createGroupFromResultSet(resultSet));
                }
                return groups;
            }
        } catch (SQLException e) {
            e.printStackTrace();
            return null;
        }
    }

这是我非常糟糕的解决方案。

 //field values: 1- create String, 2 - createAccount, 3 - createGroup
private <E> List<E> createList(String selectSql, Long id, int field) {
    List<E> list = new ArrayList<>();
    try (PreparedStatement statement = this.connection.prepareStatement(selectSql)) {
        statement.setLong(1, id);
        try (ResultSet resultSet = statement.executeQuery()) {
            while (resultSet.next()) {
                switch (field) {
                    case 1:
                        list.add((E) resultSet.getString("phoneNumber"));
                        break;
                    case 2:
                        list.add((E) createSimpleElement(resultSet));
                        break;
                    case 3:
                        list.add((E) createGroupFromResultSet(resultSet));
                        break;
                }
            }
            return list;
        }
    } catch (SQLException e) {
        e.printStackTrace();
        return null;
    }
}

我可以阅读什么来解决我的代码中的类似问题？

【问题讨论】：

不要。拥有只做一件事并做好的方法是一种很好的做法。如果需要，您可以随时使用接口或抽象类。
你可以阅读设计模式并通过编写代码来尝试它们，tutorialspoint.com/design_pattern

标签： java jdbc dao

【解决方案1】：

在我看来，您应该查看Spring JDBC，它是基于回调的JdbcTemplate 方法。它将所有样板文件（数据库连接、事务、异常翻译等）从您手中抽象出来，让您专注于应用程序代码。

示例：

List<Actor> actors = this.jdbcTemplate.query(
        "select first_name, last_name from t_actor",
        new RowMapper<Actor>() {
            public Actor mapRow(ResultSet rs, int rowNum) throws SQLException {
                Actor actor = new Actor();
                actor.setFirstName(rs.getString("first_name"));
                actor.setLastName(rs.getString("last_name"));
                return actor;
            }
        });

【讨论】：

【解决方案2】：

“将变化与保持不变的内容分开” - Head First Design Pattern。

您可以将从Resultset（更改）中提取数据的逻辑与准备语句和执行语句（不更改）分开

如果您不想从任何框架支持中获得帮助，您可以执行以下操作

public interface GenericDao {
    ResultSet find(String sqlStatement, Long id);
}

public class GenericDaoImpl extends GenericDao {
    @Override
    public ResultSet find(String sqlStatement, Long id) {
        try (PreparedStatement statement = this.connection.prepareStatement(sqlStatement)) {
            statement.setLong(1, id);
            try (ResultSet resultSet = statement.executeQuery()) {
                return resultSet;
            }
        } catch (SQLException e) {
            e.printStackTrace();
            return null;
        }
    }
}

public interface ContactDao {
    List<String> createPhoneNumbers(String sqlStatement, Long id);
    List<Account> createFriendList(String sqlStatement, Long id);
    List<Group> createGroupList(String sqlStatement, Long id);
}

public class ContactDaoImpl extends ContactDao{
    private GenericDao genericDao;

    ContactDaoImpl(GenericDao genericDao) {
        this.genericDao = genericDao;
    }

    @Override
    public List<String> createPhoneNumbers(String sqlStatement, Long id) {
        ResultSet resultSet = this.genericDao.executeSqlQuery(sqlStatement, id);
        while (resultSet.next()) {
            phones.add(resultSet.getString("phoneNumber"));
        }
        return phones;
    }

    @Override
    public List<Account> createFriendList(String sqlStatement, Long id) {
        ResultSet resultSet = this.genericDao.executeSqlQuery(sqlStatement, id);
        while (resultSet.next()) {
            friends.add(createSimpleElement(resultSet));
        }
        return friends;
    }

    @Override
    public List<Group> createGroupList(String sqlStatement, Long id) {
        ResultSet resultSet = this.genericDao.executeSqlQuery(sqlStatement, id);
        while (resultSet.next()) {
            groups.add(createGroupFromResultSet(resultSet));
        }
        return groups;
    }
}

【讨论】：