[英]Exception during connection to JDBC MySQL
下午好:我是西班牙的化學老師。 我不是經過實驗的程序員,但我決定創建一個小程序來幫助學生學習本學科。 我正在用Java創建這個小程序,我試圖與數據庫連接以便通過原子序號接收其信息。 實際上,我也想通過其他參數來做到這一點,但是我不知道該怎么做。 事實是,它會彈出異常或無法正確連接到數據庫。 我輸入了完整的代碼和數據庫的屏幕快照(順便說一句,當我嘗試將數據上傳到數據庫時,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());
}
}
}
這是我的數據庫:
這是將1插入NAt時的例外情況:
看看您select
查詢周圍的代碼,您正在運行
nat.setText("");
接着
ResultSet registro = comando.executeQuery("select elemento,simbolo,oxidacion,matom from form where natom="+nat.getText());
您期望nat.getText()
返回什么?
當然,它將返回""
因為這就是您將nat
文本設置為的內容。 然后,您要讓數據庫運行以下無效查詢:
select elemento,simbolo,oxidacion,matom from form where natom=
針對MySQL數據庫運行此操作將在您的屏幕截圖中生成錯誤。
我猜想解決辦法是刪除行nat.setText("");
。
但是,不要使用字符串連接構建SQL字符串,而應使用PreparedStatement
。
更換線
Statement comando=conexion.createStatement();
ResultSet registro = comando.executeQuery("select elemento,simbolo,oxidacion,matom from form where natom="+nat.getText());
同
PreparedStatement comando=conexion.prepareStatement(
"select elemento,simbolo,oxidacion,matom from form where natom=?");
comando.setInt(1, Integer.parseInt(nat.getText()));
ResultSet registro = comando.executeQuery();
和線
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()+")");
同
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();
您還需要在對Integer.parseInt(...)
的調用周圍添加一些錯誤處理:如果nat.getText()
或mat.getText()
不是有效的整數,則這些調用將引發NumberFormatException
。
如果您可以附加或准確描述sqlException是什么,可能會有所幫助,但是從我的角度來看,您的數據庫連接URL格式錯誤。 所以它可能沒有連接到數據庫
您的網址是: Connection conexion = DriverManager.getConnection("jdbc:mysql://localhost/chem","root" ,"");
通常,您需要添加數據庫正在運行的端口號,以便更改:
"jdbc:mysql://localhost/chem"
至:
jdbc:mysql://localhost:3306/chem
或數據庫正在運行的任何端口,從Google看來默認端口號是3360,但這取決於您如何設置數據庫。 但是我認為應該可以解決您的問題
請嘗試使用數據庫客戶端手動執行SQL查詢。 為此,您可以添加如下代碼或使用調試來獲取sql字符串值並對其進行測試:
String sqlString = "insert into form(elemento,simbolo,oxidacion,natom,matom) values ('"+elm.getText()+"','"+smb.getText()+"','"+ox.getText()+"',"+nat.getText()+","+mat.getText()+")";
System.out.println(sqlString);
comando.executeUpdate(sqlString);
您需要獲取實際的SQL字符串並對其進行手動測試(如果可行)。
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.