DAO层代码检查

Question

请查看我下面的DAO层代码。

public List<Channel> getListOfChannels() throws DataAccessException {
        // will have the channel in form of List
        // to hold the channels list
        List<Channel> listChannels = null;
        Connection conn = null;
        Statement statement = null;
        ResultSet resultSet = null;

        try {
            // get the db connection from pool
                // this is DBCP lib on top doing this 
            conn = ManageConnections.getConnection();
            statement = conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,
                    ResultSet.CONCUR_READ_ONLY);

            final String QUERY_STRING = "Select * from channel";
            resultSet = statement.executeQuery(QUERY_STRING);

            // is this good practice to put this ?
            if (isResultSetEmptyOrNull(resultSet)) {
                throw new DataAccessException(
                        "No more data of Channels found from db");
            }

            Channel channel = null;

            listChannels = new ArrayList<Channel>();

            while (resultSet.next()) {
                // get the object from the result set and 


                listChannels.add(channel);
            }

            log.debug("getListOfChannels Got the list of channels "
                    + listChannels);

                } catch (SQLException ex) {
            throw new DataAccessException(SQL_EXCEPTION + ex, ex);
        } catch (DBConnectionException ex) {
            // re thrown, no logging
            throw new DataAccessException(ex);
        } catch (Exception ex) {
            // Generic exception thrown , now throw Custom Exceptionn
            throw new DataAccessException(GENERIC_EXCEPTION + ex, ex);
        } finally {
            try {
                if (conn != null) {
                    // this is DBCP lib on top doing this 
                    ManageConnections.close(conn);
                }
                if (statement != null) {
                    statement.close();
                }
                if (resultSet != null) {
                    resultSet.close();
                }
            } catch (SQLException ex) {
                throw new DataAccessException(
                        "Exception while closing resource" + ex, ex);
            } catch (DBConnectionException ex) {
                throw new DataAccessException(
                        "Exception while closing resource" + ex, ex);
            }
        }

        return listChannels;

Answer 1

在这里可以做一些改进：

• a)你的QUERY_STRING是一根神奇的绳子。将它移到另一个地方，因为它会使您的代码难以维护。
• 用户链接列表而不是数组列表。在最坏情况下插入时有O(1)，而数组列表有O(n)
• 不要在最后块中重新抛出异常。您将丢失原始异常的所有细节。
• 每次将字符串与"+“连接时，都会使用内存执行太多操作，因为字符串是不可变的。使用*.format代替