连接关闭后结果集被清除。 SQLite

Question

这是我的代码

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 块始终为假。但是当这段代码变成这样时：

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。并且 IF 块可以为真。我想 ResultSet 在连接关闭时会重置。为什么会发生这种情况以及如何防止这种情况？

Answer 1

我想通了。不得关闭准备好的语句以保存 ResultSet。所以这有效：

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();
    }
}

连接关闭后结果集被清除。 SQLite

ResultSet cleared after connection close. SQLite

java

sqlite

connection

resultset

java-8