java - 登录表单 Java MySQL 在 intellij 中失败

Question

我已经制作了一个与 MySQL 连接连接的 javaFx 登录表单，但是当我尝试登录时，我得到了错误的名称和密码，我将提供我的代码和 MySQL 的屏幕截图，这样任何试图帮助的人都不会感到困惑

package sample;

import javafx.application.Application;
import javafx.geometry.Insets;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.*;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.HBox;
import javafx.scene.layout.VBox;
import javafx.scene.paint.Color;
import javafx.scene.shape.Rectangle;
import javafx.scene.text.Font;
import javafx.stage.Stage;


import java.sql.*;
import java.util.logging.Level;
import java.util.logging.Logger;

public class DataBaseProject1 extends Application {

    Connection conn;
    PreparedStatement pst = null;
    ResultSet rs = null;

    @Override
    public void start(Stage primaryStage) throws Exception
    {
        //GUIS a = new GUIS();
        //a.createConnection();
        //a.display();
        DataBaseProject1 d = new DataBaseProject1();
        d.createConnection();

        primaryStage.setTitle("Retrive Database Values Into CheckBox");

        //primaryStage.getIcons().add(new Image("file:user-icon.png"));
        BorderPane layout = new BorderPane();
        Scene newscene = new Scene(layout, 1200, 700, Color.rgb(0, 0, 0, 0));

        Group root = new Group();
        Scene scene = new Scene(root, 320, 200, Color.rgb(0, 0, 0, 0));
        scene.getStylesheets().add(getClass().getResource("Style.css").toExternalForm());

        Color foreground = Color.rgb(255, 255, 255, 0.9);

        //Rectangila Background
        Rectangle background = new Rectangle(320, 250);
        background.setX(0);
        background.setY(0);
        background.setArcHeight(15);
        background.setArcWidth(15);
        background.setFill(Color.rgb(0 ,0 , 0, 0.55));
        background.setStroke(foreground);
        background.setStrokeWidth(1.5);

        VBox vbox = new VBox(5);
        vbox.setPadding(new Insets(10,0,0,10));

        Label label = new Label("Label");
        //label.setTextFill(Color.WHITESMOKE);
        label.setFont(new Font("SanSerif", 20));

        TextField username = new TextField();
        username.setFont(Font.font("SanSerif", 20));
        username.setPromptText("Username");
        username.getStyleClass().add("field-background");

        PasswordField password =new PasswordField();
        password.setFont(Font.font("SanSerif", 20));
        password.setPromptText("Password");
        password.getStyleClass().add("field-background");

        Button btn = new Button("Login");
        btn.setFont(Font.font("SanSerif", 15));
        btn.setOnAction(e ->{
            try{
                String user = username.getText();
                String pass = password.getText();
                String query = "SELECT * FROM userdatabasetable Where UserName = " + "'" + user + "'" + " AND Password = " + "'" +pass + "'" + " ";

                rs = pst.executeQuery(query);

                if(rs.next()){
                    label.setText("Login Successful");
                    primaryStage.setScene(newscene);
                    primaryStage.show();
                }else{
                    label.setText("Login Failed");
                }
                username.clear();
                password.clear();
                pst.close();
                rs.close();
            }catch(Exception e1){
                label.setText("SQL Error");
                System.out.println("Wrong UserName Or Password");
                //System.err.println(e1);
            }
        });

        vbox.getChildren().addAll(label, username, password, btn);
        root.getChildren().addAll(background, vbox);

        primaryStage.setScene(scene);
        primaryStage.show();
    }

    public static void main(String[] args)
    {
        launch(args);
    }

    Connection createConnection ()
    {
        try
        {
            //Class.forName("com.mysql.jdbc.Driver");
            Class.forName("com.mysql.cj.jdbc.Driver");
            Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/UserDataBase","yusof","1234");
            System.out.println("DataBase Connected Successfully");

            //con.close();
        }
        catch (ClassNotFoundException | SQLException ex)
        {
            Logger.getLogger(DataBaseProject1.class.getName()).log(Level.SEVERE, null, ex);
        }
        return null;
    }
}

输出：

数据库连接成功 用户名或密码错误

MySQL 的屏幕截图：在此处输入图像描述

标签： javamysqldatabasejdbc

Answer 1

你没有初始化 PreparedStatement 变量，只是用空值声明PreparedStatement pst = null;

所以当语句rs = pst.executeQuery(query);执行时抛出错误。在你的 catch 块中你只写了System.out.println("Wrong UserName Or Password");. 所以你收到错误“错误的用户名或密码”

pst但实际错误是您在执行查询之前没有初始化 PreparedStatement变量。

所以初始化pst变量来解决你的问题

如果您想知道如何使用准备好的语句，那么您可以从这里看到示例

我已经解决了您代码的所有问题，所以您只需复制并粘贴以下代码即可，希望对您有所帮助

package sample;

import javafx.application.Application;
import javafx.geometry.Insets;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.*;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.HBox;
import javafx.scene.layout.VBox;
import javafx.scene.paint.Color;
import javafx.scene.shape.Rectangle;
import javafx.scene.text.Font;
import javafx.stage.Stage;


import java.sql.*;
import java.util.logging.Level;
import java.util.logging.Logger;

public class DataBaseProject1 extends Application {

    Connection conn;
    PreparedStatement pst = null;
    ResultSet rs = null;

    @Override
    public void start(Stage primaryStage) throws Exception
    {
        //GUIS a = new GUIS();
        //a.createConnection();
        //a.display();
        DataBaseProject1 d = new DataBaseProject1();
        d.createConnection();

        primaryStage.setTitle("Retrive Database Values Into CheckBox");

        //primaryStage.getIcons().add(new Image("file:user-icon.png"));
        BorderPane layout = new BorderPane();
        Scene newscene = new Scene(layout, 1200, 700, Color.rgb(0, 0, 0, 0));

        Group root = new Group();
        Scene scene = new Scene(root, 320, 200, Color.rgb(0, 0, 0, 0));
        scene.getStylesheets().add(getClass().getResource("Style.css").toExternalForm());

        Color foreground = Color.rgb(255, 255, 255, 0.9);

        //Rectangila Background
        Rectangle background = new Rectangle(320, 250);
        background.setX(0);
        background.setY(0);
        background.setArcHeight(15);
        background.setArcWidth(15);
        background.setFill(Color.rgb(0 ,0 , 0, 0.55));
        background.setStroke(foreground);
        background.setStrokeWidth(1.5);

        VBox vbox = new VBox(5);
        vbox.setPadding(new Insets(10,0,0,10));

        Label label = new Label("Label");
        //label.setTextFill(Color.WHITESMOKE);
        label.setFont(new Font("SanSerif", 20));

        TextField username = new TextField();
        username.setFont(Font.font("SanSerif", 20));
        username.setPromptText("Username");
        username.getStyleClass().add("field-background");

        PasswordField password =new PasswordField();
        password.setFont(Font.font("SanSerif", 20));
        password.setPromptText("Password");
        password.getStyleClass().add("field-background");

        Button btn = new Button("Login");
        btn.setFont(Font.font("SanSerif", 15));
        btn.setOnAction(e ->{
            try{
                String user = username.getText();
                String pass = password.getText();
                String query = "SELECT * FROM userdatabasetable Where UserName = " + "'" + user + "'" + " AND Password = " + "'" +pass + "'" + " ";
                d.pst=d.conn.prepareStatement(query);
                rs = d.pst.executeQuery(query);

                if(rs.next()){
                    label.setText("Login Successful");
                    primaryStage.setScene(newscene);
                    primaryStage.show();
                }else{
                    label.setText("Login Failed");
                }
                username.clear();
                password.clear();
                d.pst.close();
                rs.close();
            }catch(Exception e1){
                label.setText("SQL Error");
                System.out.println("Wrong UserName Or Password");
                //System.err.println(e1);
               // e1.printStackTrace();
            }
        });

        vbox.getChildren().addAll(label, username, password, btn);
        root.getChildren().addAll(background, vbox);

        primaryStage.setScene(scene);
        primaryStage.show();
    }

    public static void main(String[] args)
    {
        launch(args);
    }

    Connection createConnection ()
    {
        try
        {
            //Class.forName("com.mysql.jdbc.Driver");
            Class.forName("com.mysql.cj.jdbc.Driver");
            conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/UserDataBase","yusof","1234");
            System.out.println("DataBase Connected Successfully");

            //con.close();
        }
        catch (ClassNotFoundException | SQLException ex)
        {
            Logger.getLogger(DataBaseProject1.class.getName()).log(Level.SEVERE, null, ex);
        }
        return null;
    }
}