ResultSet始终返回null，无论JDBC/MySQL、Java中的更改如何

Question

package graphical_interface;
import business_logic.User;
import javafx.application.Platform;
import javafx.fxml.FXML;
import javafx.scene.Parent;
import javafx.scene.control.Button;
import javafx.scene.control.TextField;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;

public class Controller {
    @FXML
    public Button loginB;
    public Button exitB;
    public TextField userinp;
    public TextField passinp;
    public Parent pr;
    public static String s1 = null;
    public static String s2 = null;
    @FXML
    private void closeApp() {
        Platform.exit();
    }
    String username = null;
    String password = null;
    @FXML
    private void checkB(){

            try {
                PreparedStatement pstmt2 = null;
                Class.forName("com.mysql.jdbc.Driver");
                Connection conn = DriverManager.getConnection("jdbc:mysql://remotemysql.com/CXcocPWj6l", "CXcocPWj6l", "czNrEV9umD");
                String query  = "select * from User where Username = ? and PassWord = ?";
                pstmt2.setString(1,userinp.getText());
                pstmt2.setString(2,passinp.getText());
                ResultSet valueExist = pstmt2.executeQuery(query);
                if(valueExist.next()){
                    s1 = valueExist.getString("Username");
                    s2 = valueExist.getString("PassWord");
                   // System.out.println(valueExist.getString("PassWord");
                }
                conn.close();
                System.out.println(s1);
                System.out.println(s2);

            } catch (Exception exp){
                System.out.println(exp.getLocalizedMessage());
            }
    }
}

Answer 1

将columnLabel替换为columnIndex，即替换

if(valueExist.next()){
    s1 = valueExist.getString("Username");
    s2 = valueExist.getString("PassWord");
}

与

if(valueExist!=null && valueExist.next()){
    s1 = valueExist.getString(columnIndex-of-Username);
    s2 = valueExist.getString(columnIndex-of-PassWord);
}

其中columnindex-of-username和columnindex-of-password是整数值，分别保存username和password的columnIndex。