java - 连接 JDBC MySQL 时出现异常

Question

下午好:我是来自西类牙的化学老师。我不是一个经验丰富的程序员，但我决定创建一个小程序来帮助我的学生完成我的主题。我正在用 Java 创建这个小程序，我试图连接数据库以便通过原子数接收其信息。其实我也想通过其他参数来做到这一点，但我不知道该怎么做。问题是它反弹了异常或者它没有正确连接到数据库。我附上了完整的代码和数据库的屏幕截图(顺便说一句，当我尝试将数据上传到数据库时，它可以工作。):

package chemInterface;

import java.awt.BorderLayout;
import java.awt.EventQueue;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;



import java.awt.Color;
import java.awt.Font;
import javax.swing.JLabel;
import javax.swing.JPasswordField;
import javax.swing.JTextField;
import javax.swing.JButton;
import java.awt.event.ActionListener;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;
import java.sql.Connection;
import java.sql.ResultSet;
import java.awt.event.ActionEvent;

public class Oxidaciones extends JFrame {

private JPanel contentPane;
private JPasswordField pass;
private JTextField smb;
private JTextField elm;
private JTextField ox;
private JTextField nat;
private JTextField mat;

/**
 * Launch the application.
 */
public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                Oxidaciones frame = new Oxidaciones();
                frame.setVisible(true);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
}

/**
 * Create the frame.
 */
public Oxidaciones() {
    setFont(new Font("Courier Prime", Font.PLAIN, 12));
    setTitle("Interface");
    setForeground(Color.BLUE);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setBounds(100, 100, 450, 300);
    contentPane = new JPanel();
    contentPane.setForeground(Color.BLUE);
    contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
    setContentPane(contentPane);
    contentPane.setLayout(null);

    JLabel lblSmbolo = new JLabel("Smb");
    lblSmbolo.setFont(new Font("Courier Prime", Font.PLAIN, 11));
    lblSmbolo.setBounds(10, 30, 67, 14);
    contentPane.add(lblSmbolo);

    JLabel lblElemento = new JLabel("Elm");
    lblElemento.setFont(new Font("Courier Prime", Font.PLAIN, 11));
    lblElemento.setBounds(10, 52, 67, 14);
    contentPane.add(lblElemento);

    JLabel lblOxidacin = new JLabel("Ox");
    lblOxidacin.setFont(new Font("Courier Prime", Font.PLAIN, 11));
    lblOxidacin.setBounds(10, 77, 67, 14);
    contentPane.add(lblOxidacin);

    JLabel lblNAtmico = new JLabel("NAt");
    lblNAtmico.setFont(new Font("Courier Prime", Font.PLAIN, 11));
    lblNAtmico.setBounds(10, 102, 86, 14);
    contentPane.add(lblNAtmico);

    JLabel lblMAtmica = new JLabel("MAt");
    lblMAtmica.setFont(new Font("Courier Prime", Font.PLAIN, 11));
    lblMAtmica.setBounds(10, 127, 86, 14);
    contentPane.add(lblMAtmica);

    pass = new JPasswordField();
    pass.setBounds(90, 166, 67, 20);
    contentPane.add(pass);

    JLabel lblPass = new JLabel("Pass");
    lblPass.setFont(new Font("Courier Prime", Font.PLAIN, 11));
    lblPass.setBounds(10, 169, 67, 14);
    contentPane.add(lblPass);

    smb = new JTextField();
    smb.setBounds(67, 25, 86, 20);
    contentPane.add(smb);
    smb.setColumns(10);

    elm = new JTextField();
    elm.setColumns(10);
    elm.setBounds(67, 47, 86, 20);
    contentPane.add(elm);

    ox = new JTextField();
    ox.setColumns(10);
    ox.setBounds(67, 72, 86, 20);
    contentPane.add(ox);

    nat = new JTextField();
    nat.setColumns(10);
    nat.setBounds(67, 97, 86, 20);
    contentPane.add(nat);

    mat = new JTextField();
    mat.setColumns(10);
    mat.setBounds(67, 127, 86, 20);
    contentPane.add(mat);

    JLabel lblResultado = new JLabel("");
    lblResultado.setBounds(243, 232, 46, 14);
    contentPane.add(lblResultado);


    JButton compile = new JButton("Compile");
    compile.addActionListener(new ActionListener() {
        @SuppressWarnings("deprecation")
        public void actionPerformed(ActionEvent arg0) {


            //COMPILE Presionado



                //INSERT BETWEEN HERE

                ox.setText("");
                elm.setText("");
                mat.setText("");
                nat.setText("");
                smb.setText("");

                try {
                Connection conexion=DriverManager.getConnection("jdbc:mysql://localhost/chem","root" ,"");
                Statement comando=conexion.createStatement();
                ResultSet registro = comando.executeQuery("select elemento,simbolo,oxidacion,matom from form where natom="+nat.getText());
                if(registro.next()==true) {
                    smb.setText(registro.getString("simbolo"));
                    ox.setText(registro.getString("oxidacion"));
                    elm.setText(registro.getString("elemento"));
                    mat.setText(registro.getString("matom"));
                } else {lblResultado.setText("No existe");}
                conexion.close();
                } catch(SQLException ex) {setTitle(ex.toString());}





            //AND HERE  

            }






    });
    compile.setBounds(7, 194, 89, 23);
    contentPane.add(compile);

    JButton clear = new JButton("Clear");
    clear.setBounds(7, 228, 89, 23);
    contentPane.add(clear);

    JButton alta = new JButton("Alta");
    alta.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent arg0) {


            //BOTON ALTA PRESIONADO

            lblResultado.setText("");

            try {
                  Connection conexion=DriverManager.getConnection("jdbc:mysql://localhost/chem","root", "");
                  Statement comando=conexion.createStatement();
                  comando.executeUpdate("insert into form(elemento,simbolo,oxidacion,natom,matom) values ('"+elm.getText()+"','"+smb.getText()+"','"+ox.getText()+"',"+nat.getText()+","+mat.getText()+")");
                  conexion.close();
                  lblResultado.setText("se registraron los datos");
                  elm.setText("");
                  ox.setText("");
                  nat.setText("");
                  mat.setText("");
                  smb.setText("");
                } catch(SQLException ex){
                  setTitle(ex.toString());
                }

        }
    });
    alta.setBounds(335, 228, 89, 23);
    contentPane.add(alta);


    cargarDriver();
}

private void cargarDriver() {
    try {
        Class.forName("com.mysql.jdbc.Driver");
    }
    catch(Exception ex) {
        setTitle(ex.toString());
    }
}
}

这是我的数据库:

database phpmyadmin

这是将 1 插入 NAt 时的异常(exception)情况:

Actual Exception

Answer 1

查看一下 select 查询周围的代码，您正在运行

            nat.setText("");

然后

            ResultSet registro = comando.executeQuery("select elemento,simbolo,oxidacion,matom from form where natom="+nat.getText());

您期望 nat.getText() 在此处返回什么？

当然，它会返回 ""，因为这就是您设置的 nat 文本。然后，您要求数据库运行以下无效查询:

    select elemento,simbolo,oxidacion,matom from form where natom=

针对 MySQL 数据库运行此操作将在屏幕截图中生成错误。

我猜测修复方法是删除 nat.setText(""); 行。

但是，请使用 PreparedStatement，而不是使用字符串连接来构建 SQL 字符串。改为 s。

更换线路

            Statement comando=conexion.createStatement();
            ResultSet registro = comando.executeQuery("select elemento,simbolo,oxidacion,matom from form where natom="+nat.getText());

与

            PreparedStatement comando=conexion.prepareStatement(
                "select elemento,simbolo,oxidacion,matom from form where natom=?");
            comando.setInt(1, Integer.parseInt(nat.getText()));
            ResultSet registro = comando.executeQuery();

和线条

              Statement comando=conexion.createStatement();
              comando.executeUpdate("insert into form(elemento,simbolo,oxidacion,natom,matom) values ('"+elm.getText()+"','"+smb.getText()+"','"+ox.getText()+"',"+nat.getText()+","+mat.getText()+")");

与

              Statement comando=conexion.prepareStatement(
                  "insert into form(elemento,simbolo,oxidacion,natom,matom) values (?,?,?,?,?)");
              comando.setString(1, elm.getText());
              comando.setString(2, smb.getText());
              comando.setString(3, ox.getText());
              comando.setString(4, Integer.parseInt(nat.getText()));
              comando.setString(5, Integer.parseInt(mat.getText()));
              comando.executeUpdate();

您还需要在对 Integer.parseInt(...) 的调用周围添加一些错误处理:如果 nat ，这些将抛出 NumberFormatException .getText() 或 mat.getText() 不是有效的整数。