private MySql ms = new MySql();
//省略部分无关代码
btnSave.addActionListener(new ActionListener(){
            @Override
            public void actionPerformed(ActionEvent e) {
                // TODO Auto-generated method stub
                String sql = "INSERT INTO student VALUES("+txtId.getText()+",'"+txtName.getText()+"');";
                ms.ExecuteSql(sql);
                ms.closeConnection();
                showStu();
            }
            
        });

public class MySql {
    private Connection conn =null;
    private final String DB_DRIVER="com.mysql.jdbc.Driver";
    private final String DB_URL="jdbc:mysql://localhost:3306/school";
    private final String DB_USER="root";
    private final String DB_PWD="root";
    public MySql(){}
    public void getConnection(){
        try {
            Class.forName(DB_DRIVER);
            Connection conn = DriverManager.getConnection(DB_URL, DB_USER, DB_PWD);
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    public void closeConnection(){
        try {
            if(conn!=null){
                conn.close();
            }
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    public boolean ExecuteSql(String sql){
        int rt=0;
        if(conn==null){
            getConnection();
        }
        try {
            Statement stm = conn.createStatement();
            stm.executeUpdate(sql);
            //stm.close();
                        //不管有没有这个close都会有异常
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        if(rt==0){
            return false;
        }else{
            return true;
        }
        
    }