当我试图将数据保存到 mysql 时，抛出异常（java.sql.SQLException）

Question

import java.awt.Panel;

import java.awt.event.ActionEvent;

import java.awt.event.ActionListener;

import java.sql.DriverManager;

import java.sql.PreparedStatement;

import java.sql.ResultSet;

import java.sql.Statement;

import javax.swing.JButton;

import javax.swing.JFrame;

import javax.swing.JLabel;

import javax.swing.JTextField;

import com.mysql.jdbc.Connection;

public class one implements ActionListener{

    JFrame frame = new JFrame("ghar hisab");
    JButton b = new JButton("save");
    Panel p = new Panel();
    JTextField f = new JTextField(20);
    JTextField f1 = new JTextField(20);
    JLabel l = new JLabel("Enter the first name");
    JLabel l1 = new JLabel("Enter the last name");
    String s1,s2;
    String ppl;
    int people;

            void display() throws Exception{
                                p.add(l);
                                p.add(f);
                                p.add(l1);
                                p.add(f1);
                                p.add(b);

                                frame.setSize(400,400);

                                frame.setVisible(true);
                                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                                frame.getContentPane().add(p);
                                s1=f.getText();
                                s2=f1.getText();


                //Class.forName("com.mysql.jdbc.Driver");
                //Connection con = (Connection) DriverManager.getConnection("jdbc:mysql://localhost:3306/people","root","desire");

                //Statement stat = con.createStatement();
            //  String s3= "insert into name values s1 + s2";
            //  stat.executeUpdate(s3);



        //  stat.executeQuery("insert into name (first,last) values('"+s1+"','"+s2+"')");
            b.addActionListener(this);

        //  ResultSet rs= stat.executeQuery("insert into name (first,last) values("arun","yadav"));


            //while(rs.next()){
        //      System.out.println(rs.getString(1)+" "+rs.getString(2));
        //  }




        }

        @Override
        public void actionPerformed(ActionEvent event) {
            // TODO Auto-generated method stub
            try{
                Class.forName("com.mysql.jdbc.Driver");

            Connection con = (Connection) DriverManager.getConnection("jdbc:mysql://localhost:3306/people","root","desire");

            Statement stat = con.createStatement();

            stat.executeQuery("insert into name (first,last) values('"+s1+"','"+s2+"')");
            }
            catch(Exception e){
                System.out.println("the exception caught is "+e);
            }
        }


}

Answer 1

没有堆栈跟踪，很难分辨。要么您没有建立连接，要么您的 SQL 中的值导致查询出错（可能一个或两个都为空）。我建议在 con 上设置一个断点，看看对象是否为空。并查看 s1 和 s2 是什么。下面，我添加了两行。您需要关闭您的语句和连接。

public void actionPerformed(ActionEvent event) {
    // TODO Auto-generated method stub
    try
    {
        Class.forName("com.mysql.jdbc.Driver");
        Connection con = (Connection) DriverManager.getConnection("jdbc:mysql://localhost:3306/people","root","desire");
        Statement stat = con.createStatement();
        stat.executeQuery("insert into name (first,last) values('"+s1+"','"+s2+"')");
        stat.close();
        con.close();
    }
    catch(Exception e){
        System.out.println("e.fillInStackTrace:" + e.fillInStackTrace());
        System.out.println("e.getCause:" + e.getCause());
        System.out.println("e.getLocalizedMessage:" + e.getLocalizedMessage());
        System.out.println("e.getMessage.:" + e.getMessage());
        System.out.println("e.getStackTrace:" + e.getStackTrace());
        System.out.println("e.initCause:" + e.initCause());
        System.out.println("e.printStackTrace:" + e.printStackTrace());
        System.out.println("e.toString:" + e.toString());       
    }
}

Answer 2

我注意到您导入 PreparedStatement，但您的代码从未使用它。好吧，我对 SQL 了解不多，但是当您使用 PreparedStatement 时，我这样做的可能性较小。下面是一个简单的插入示例：

String sql = "INSERT INTO Name (First, Last) VALUES (?, ?)";

PreparedStatement stmt = connection.prepareStatement(sql);

stmt.setString( 1, s1 );
stmt.setString( 2, s2 );
stmt.executeUpdate();

我冒昧地将表名和列名大写，因为这是大多数人创建表名的方式。

编辑：

s1=f.getText();
s2=f1.getText(); 

执行该代码时，文本字段不包含任何值，因为用户还没有机会在文本字段中输入任何数据。这两条语句需要移到 actionPerformed() 方法中。