我如何在不重复的情况下重写这些方法？

Question

如何使这段代码不重复？这种方法是相似的。

创建phone个号码的方法：

   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;
        }
    }

创建群组列表的方法：

   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;
    }
}

我可以阅读哪些内容来解决我的代码中的类似问题？

Answer 1

我觉得你应该检查一下 Spring JDBC and it's callback-based JdbcTemplate 方法。它将所有样板文件（数据库连接、事务、异常转换等）从您身上抽象出来，让您专注于应用程序代码。

样本：

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;
            }
        });

Answer 2

"Separate what changes from what stays same" - Head First 设计模式。

您可以将从 Resultset 中提取数据（发生变化）的逻辑与准备语句和执行语句（不发生变化）分开

如果您不想从任何框架支持中获得帮助，您可以执行如下操作

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;
    }
}

我如何在不重复的情况下重写这些方法？

How can i rewrite this methods without duplication?

java

dao

jdbc