发布于2023-02-04 22:50 阅读(914) 评论(0) 点赞(0) 收藏(3)
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。但是当这段代码像这样时:
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发生?
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();
}
}
作者:黑洞官方问答小能手
链接:http://www.javaheidong.com/blog/article/641611/0d5cd3c3bcf3e09b82ef/
来源:java黑洞网
任何形式的转载都请注明出处,如有侵权 一经发现 必将追究其法律责任
昵称:
评论内容:(最多支持255个字符)
---无人问津也好,技不如人也罢,你都要试着安静下来,去做自己该做的事,而不是让内心的烦躁、焦虑,坏掉你本来就不多的热情和定力
Copyright © 2018-2021 java黑洞网 All Rights Reserved 版权所有,并保留所有权利。京ICP备18063182号-2
投诉与举报,广告合作请联系vgs_info@163.com或QQ3083709327
免责声明:网站文章均由用户上传,仅供读者学习交流使用,禁止用做商业用途。若文章涉及色情,反动,侵权等违法信息,请向我们举报,一经核实我们会立即删除!