是否可以在 java 中传递结果集？

Question

我正在尝试创建一个命令，我可以将不同的查询发送到 SQLite / Mysql DB，并将结果集返回给正在调用的任何函数。它需要能够处理是 2 列还是 15 列。

以下不起作用 - 大概是因为它关闭了结果集/连接，但我不知道该怎么做。

想法？

public static ResultSet queryDB(String query) {

    try {

        Connection connection = DriverManager.getConnection("jdbc:sqlite:" + Settings.SQLITE_DB_PATH);

        Statement statement = connection.createStatement();

        ResultSet resultSet = statement.executeQuery(query);

        resultSet.close();

        statement.close();

        connection.close();

        return resultSet;

    } catch (SQLException ex) {

        Logger.getLogger(SQLInterp.class.getName()).log(Level.SEVERE, null, ex);

    }

    return null;

}

Answer 1

你基本上有3个选择：不要关闭方法中的ResultSet,Statement和Connection，将执行此操作的责任移交给调用者。不推荐，因为它容易出错，并且会破坏格式良好的代码结构范例。按照Jacob G.的建议，传入具有处理数据所需逻辑的对象。例如使用 Java 8+&nbsp;Consumer：public static void queryDB(String query, Consumer<ResultSet> processor) {&nbsp; &nbsp; try (&nbsp; &nbsp; &nbsp; &nbsp; Connection connection = DriverManager.getConnection("jdbc:sqlite:" + Settings.SQLITE_DB_PATH);&nbsp; &nbsp; &nbsp; &nbsp; Statement statement = connection.createStatement();&nbsp; &nbsp; &nbsp; &nbsp; ResultSet resultSet = statement.executeQuery(query);&nbsp; &nbsp; ) {&nbsp; &nbsp; &nbsp; &nbsp; processor.accept(resultSet);&nbsp; &nbsp; } catch (SQLException ex) {&nbsp; &nbsp; &nbsp; &nbsp; Logger.getLogger(SQLInterp.class.getName()).log(Level.SEVERE, null, ex);&nbsp; &nbsp; }}然后像这样调用它：SQLInterp.queryDB("SELECT * FROM foo", rs -> {&nbsp; &nbsp; while (rs.next()) {&nbsp; &nbsp; &nbsp; &nbsp; // process data here&nbsp; &nbsp; }});以通用数据结构将所有数据读入内存，例如List<Map<String, Object>>：这当然假设查询对每一列都有很好的唯一名称。public static List<Map<String, Object>> queryDB2(String query) {&nbsp; &nbsp; try (&nbsp; &nbsp; &nbsp; &nbsp; Connection connection = DriverManager.getConnection("jdbc:sqlite:" + Settings.SQLITE_DB_PATH);&nbsp; &nbsp; &nbsp; &nbsp; Statement statement = connection.createStatement();&nbsp; &nbsp; &nbsp; &nbsp; ResultSet resultSet = statement.executeQuery(query);&nbsp; &nbsp; ) {&nbsp; &nbsp; &nbsp; &nbsp; ResultSetMetaData metaData = resultSet.getMetaData();&nbsp; &nbsp; &nbsp; &nbsp; int columnCount = metaData.getColumnCount();&nbsp; &nbsp; &nbsp; &nbsp; String[] name = new String[columnCount];&nbsp; &nbsp; &nbsp; &nbsp; for (int i = 0; i < columnCount; i++)&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; name[i] = metaData.getColumnLabel(i + 1);&nbsp; &nbsp; &nbsp; &nbsp; List<Map<String, Object>> rows = new ArrayList<>();&nbsp; &nbsp; &nbsp; &nbsp; while (resultSet.next()) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Map<String, Object> row = new LinkedHashMap<>();&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; for (int i = 0; i < columnCount; i++)&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; row.put(name[i], resultSet.getObject(i + 1));&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; rows.add(row);&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; return rows;&nbsp; &nbsp; } catch (SQLException ex) {&nbsp; &nbsp; &nbsp; &nbsp; Logger.getLogger(SQLInterp.class.getName()).log(Level.SEVERE, null, ex);&nbsp; &nbsp; }}