連接關閉后 ResultSet 被清除。 SQLite

Question

這是我的代碼

public static void main(String[] args) throws SQLException {
    Long chatId = 432878720L;
    String what = "*";
    String from = "BtcUser";
    ResultSet rs = selectUser(what, from, chatId);
    if (rs.next()) {
        System.out.println("NEVER REACH");
    }
}

private static ResultSet selectUser(String what, String from, long chatId) throws SQLException {
    String sql = "SELECT "+what+" FROM "+from+" WHERE chatId = ?;";
    ResultSet rs;
    try (Connection con = DriverManager.getConnection(url);
         PreparedStatement pst = con.prepareStatement(sql)) {
        pst.setLong(1, chatId);
        rs = pst.executeQuery();
        return rs;
    }
}

如您所料，IF 塊始終為假。 但是當這段代碼像這樣：

public static void main(String[] args) throws SQLException {
    Long chatId = 432878720L;
    String what = "*";
    String from = "BtcUser";
    String sql = "SELECT "+what+" FROM "+from+" WHERE chatId = ?;";
    ResultSet rs;
    try (Connection con = DriverManager.getConnection(url);
         PreparedStatement pst = con.prepareStatement(sql)) {
        pst.setLong(1, chatId);
        rs = pst.executeQuery();
        if (rs.next()) {
            System.out.println("HELLO");
        }
    }
}

一切正常。 並且 IF 塊可以為真。 我猜連接關閉時 ResultSet 會重置。 為什么會發生這種情況以及如何防止這種情況發生？

Answer 1

我想通了。 不得為保存 ResultSet 關閉准備好的語句。 所以這有效：

public static void main(String[] args) throws SQLException {
    long chatId = 432878720L;
    String what = "*";
    String from = "BtcUser";
    ResultSet rs = f(what, from, chatId);
    if (rs.next()) {
        System.out.println("HELLO");
    }
}

private static ResultSet f(String what, String from, long chatId) throws SQLException {
    String sql = "SELECT "+what+" FROM "+from+" WHERE chatId = ?;";
    try (Connection con = DriverManager.getConnection(url)) {
        PreparedStatement pst = con.prepareStatement(sql);
        pst.setLong(1, chatId);
        return pst.executeQuery();
    }
}