java - 使用 Java/sql 存储和检索数据时遇到问题

Question

我对 Java 相当陌生，对 sql 也不是很熟悉。我正在开发一个程序，该程序接受地板订单并将其存储在 SQL 数据库中。姓名和地址可以很好地存储，但其余信息则不会。信息检索也不起作用。我也不确定我做错了什么。出于显而易见的原因，我从 Connection 对象中删除了信息，但我可以向您保证，我的程序中包含正确的信息。任何帮助将不胜感激。

import java.awt.event.*;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.text.*;
import javax.swing.*;

public class FlooringOrders extends JFrame implements ActionListener {

private JLabel lblFloorType, lblRoomSize, lblLength, lblWidth, lblName, 
lblAddress, lblOrderInfo, lblTotal;
private JRadioButton rbtnWood, rbtnCarpet;
private JButton btnCalculate, btnSubmit, btnOrders;
private ButtonGroup grpType;
private JTabbedPane tab;
private JTextField txtLength, txtWidth, txtArea, txtName, txtAddress;
private JTextArea txtOrderInfo, txtTotal, txtCustomer;
private JPanel p1, p2, p3, p4;
private double Length, Width, Area, Total;
private String sLength, sWidth, sArea, sTotal, fType, insertQuery;
private PreparedStatement myQuery;
private ResultSet rs;
private DecimalFormat df;

public FlooringOrders() {

    super("Flooring Orders");

    df = new DecimalFormat("#,###,###.00");

    tab = new JTabbedPane();
    p1 = new JPanel();
    p2 = new JPanel();
    p3 = new JPanel();
    p4 = new JPanel();

    lblFloorType = new JLabel("Choose Floor Type: ");
    lblRoomSize = new JLabel("Enter Room Size: ");
    lblLength = new JLabel("Length (ft): ");
    lblWidth = new JLabel("Width (ft): ");
    lblName = new JLabel("Enter Name: ");
    lblAddress = new JLabel("Enter Address: ");
    lblOrderInfo = new JLabel("Order Info: ");
    lblTotal = new JLabel("Total: ");

    rbtnWood = new JRadioButton("Wood - $20/sq. ft.");
    rbtnCarpet = new JRadioButton("Carpet - $10/sq. ft.");
    grpType = new ButtonGroup();

    btnCalculate = new JButton("Calculate Area");
    btnSubmit = new JButton("Submit");
    btnOrders = new JButton("Customer Orders");

    txtLength = new JTextField(10);
    txtWidth = new JTextField(10);
    txtArea = new JTextField(10);
    txtName = new JTextField(10);
    txtAddress = new JTextField(10);

    txtOrderInfo = new JTextArea(15, 15);
    txtTotal = new JTextArea(15, 15);
    txtCustomer = new JTextArea(15, 15);

    grpType.add(rbtnCarpet);
    grpType.add(rbtnWood);

    getContentPane().add(tab);

    p1.add(lblFloorType);
    p1.add(rbtnWood);
    p1.add(rbtnCarpet);
    p1.add(lblRoomSize);
    p1.add(lblLength);
    p1.add(txtLength);
    p1.add(lblWidth);
    p1.add(txtWidth);
    p1.add(btnCalculate);
    p1.add(txtArea);
    tab.add("Flooring", p1);

    p2.add(lblName);
    p2.add(txtName);
    p2.add(lblAddress);
    p2.add(txtAddress);
    p2.add(btnSubmit);
    tab.add("Customer Info", p2);

    p3.add(lblOrderInfo);
    p3.add(txtOrderInfo);
    p3.add(lblTotal);
    p3.add(txtTotal);
    tab.add("Total", p3);

    p4.add(btnOrders);
    p4.add(txtCustomer);
    tab.add("Order List", p4);

    btnCalculate.addActionListener(this);
    btnSubmit.addActionListener(this);
    btnOrders.addActionListener(this);

} //end constructor

public void actionPerformed(ActionEvent a) {

    sLength = txtLength.getText();
    sWidth = txtWidth.getText();
    fType = "";

    Length = Double.parseDouble(sLength);
    Width = Double.parseDouble(sWidth);
    Area = 0;
    Total = 0;  

    if(a.getSource().equals(btnCalculate)) {

        Area = Length * Width;          

        if(rbtnWood.isSelected()) {

            Total = Area * 20;
            fType.equals("Wood");

        } else if(rbtnCarpet.isSelected()) {

            Total = Area * 10;
            fType.equals("Carpet");

        } //end if/else

        sArea = String.valueOf(df.format(Area));
        sTotal = String.valueOf(df.format(Total));

        txtArea.setText(sArea);
        txtTotal.setText(sTotal);

        System.out.println("Calculate Area pressed");

    } //end if

    if(a.getSource().equals(btnSubmit)) {

        newOrder();

        System.out.println("Submit pressed");

    } //end if

    if(a.getSource().equals(btnOrders)) {

        orderList();

        System.out.println("Customer Orders pressed");

    } //end if

} //end actionPerformed

public void newOrder() {

    insertQuery = "INSERT into CustomerOrders(CustomerName, CustomerAddress,
FloorType, RoomSize, Total) values(?, ?, ?, ?, ?)";

    try {

        Connection conn = DriverManager.getConnection();

        myQuery = conn.prepareStatement(insertQuery);           


        myQuery.setString(1, txtName.getText());            
        myQuery.setString(2, txtAddress.getText());
        myQuery.setString(3, fType);
        myQuery.setDouble(4, Area);
        myQuery.setDouble(5, Total);

        myQuery.execute();

        JOptionPane.showMessageDialog(null, "Thank you for your order!");   

    } catch (SQLException e) {

        // TODO Auto-generated catch block
        e.printStackTrace();

    } //end try/catch

} //end newOrder

public void orderList() {

try {

    rs = myQuery.executeQuery("SELECT * from CustomerOrders");
    ResultSetMetaData md = rs.getMetaData();
    int columns = md.getColumnCount();

        while (rs.next()) {

            for(int i = 1; i < columns; i++) {

                txtCustomer.setText(rs.getString(i) + " ");

                System.out.print(rs.getString(i) + " ");

                System.out.println();

            } //end for

        }// end while

} catch (SQLException e) {

    // TODO Auto-generated catch block
    e.printStackTrace();

}   //end try/catch

} //end orderList

} //end class

Answer 1

在 public void orderList() { 中，您应该在执行之前创建一条语句。

 myQuery = conn.createStatement( );
 rs = myQuery.executeQuery("SELECT * from CustomerOrders");

如果对您有帮助，请告诉我。

我对你的代码进行了一些重构。希望它能帮助您进步。

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.sql.Statement;
import java.text.DecimalFormat;

import javax.swing.ButtonGroup;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JRadioButton;
import javax.swing.JTabbedPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;

public class FlooringOrders extends JFrame implements ActionListener {

    private JLabel lblFloorType, lblRoomSize, lblLength, lblWidth, lblName,
            lblAddress, lblOrderInfo, lblTotal;
    private JRadioButton rbtnWood, rbtnCarpet;
    private JButton btnCalculate, btnSubmit, btnOrders;
    private ButtonGroup grpType;
    private JTabbedPane tab;
    private JTextField txtLength, txtWidth, txtArea, txtName, txtAddress;
    private JTextArea txtOrderInfo, txtTotal, txtCustomer;
    private JPanel p1, p2, p3, p4;
    private double Length, Width, Area, Total;
    private String sLength, sWidth, sArea, sTotal, fType, insertQuery;
    private PreparedStatement myQuery;
    private ResultSet rs;
    private DecimalFormat df;

    public FlooringOrders() {

        super("Flooring Orders");

        df = new DecimalFormat("#,###,###.00");

        tab = new JTabbedPane();
        p1 = new JPanel();
        p2 = new JPanel();
        p3 = new JPanel();
        p4 = new JPanel();

        lblFloorType = new JLabel("Choose Floor Type: ");
        lblRoomSize = new JLabel("Enter Room Size: ");
        lblLength = new JLabel("Length (ft): ");
        lblWidth = new JLabel("Width (ft): ");
        lblName = new JLabel("Enter Name: ");
        lblAddress = new JLabel("Enter Address: ");
        lblOrderInfo = new JLabel("Order Info: ");
        lblTotal = new JLabel("Total: ");

        rbtnWood = new JRadioButton("Wood - $20/sq. ft.");
        rbtnCarpet = new JRadioButton("Carpet - $10/sq. ft.");
        grpType = new ButtonGroup();

        btnCalculate = new JButton("Calculate Area");
        btnSubmit = new JButton("Submit");
        btnOrders = new JButton("Customer Orders");

        txtLength = new JTextField(10);
        txtWidth = new JTextField(10);
        txtArea = new JTextField(10);
        txtName = new JTextField(10);
        txtAddress = new JTextField(10);

        txtOrderInfo = new JTextArea(15, 15);
        txtTotal = new JTextArea(15, 15);
        txtCustomer = new JTextArea(15, 15);

        grpType.add(rbtnCarpet);
        grpType.add(rbtnWood);

        getContentPane().add(tab);

        p1.add(lblFloorType);
        p1.add(rbtnWood);
        p1.add(rbtnCarpet);
        p1.add(lblRoomSize);
        p1.add(lblLength);
        p1.add(txtLength);
        p1.add(lblWidth);
        p1.add(txtWidth);
        p1.add(btnCalculate);
        p1.add(txtArea);
        tab.add("Flooring", p1);

        p2.add(lblName);
        p2.add(txtName);
        p2.add(lblAddress);
        p2.add(txtAddress);
        p2.add(btnSubmit);
        tab.add("Customer Info", p2);

        p3.add(lblOrderInfo);
        p3.add(txtOrderInfo);
        p3.add(lblTotal);
        p3.add(txtTotal);
        tab.add("Total", p3);

        p4.add(btnOrders);
        p4.add(txtCustomer);
        tab.add("Order List", p4);

        btnCalculate.addActionListener(this);
        btnSubmit.addActionListener(this);
        btnOrders.addActionListener(this);

    } // end constructor

    private Connection getConnection() throws SQLException {
        return DriverManager.getConnection("");
    }

    public void actionPerformed(ActionEvent a) {
        if (a.getSource().equals(btnCalculate)) {
            sLength = txtLength.getText();
            sWidth = txtWidth.getText();
            fType = "";
            Length = sLength.isEmpty() ? 0.0 : Double.parseDouble(sLength);
            Width = sWidth.isEmpty() ? 0.0 : Double.parseDouble(sWidth);
            Area = 0;
            Total = 0;
            Area = Length * Width;
            if (rbtnWood.isSelected()) {

                Total = Area * 20;
                fType.equals("Wood");

            } else if (rbtnCarpet.isSelected()) {

                Total = Area * 10;
                fType.equals("Carpet");

            } // end if/else

            sArea = String.valueOf(df.format(Area));
            sTotal = String.valueOf(df.format(Total));
            txtArea.setText(sArea);
            txtTotal.setText(sTotal);

            System.out.println("Calculate Area pressed");

        } // end if

        if (a.getSource().equals(btnSubmit)) {

            newOrder();

            System.out.println("Submit pressed");

        } // end if

        if (a.getSource().equals(btnOrders)) {

            orderList();

            System.out.println("Customer Orders pressed");

        } // end if

    } // end actionPerformed

    public void newOrder() {
        insertQuery = "INSERT into CustomerOrders(CustomerName, CustomerAddress,FloorType, RoomSize, Total) values(?, ?, ?, ?, ?)";
        PreparedStatement ps = null;
        try {
            Connection conn = DriverManager.getConnection("");
            ps = conn.prepareStatement(insertQuery);
            ps.setString(1, txtName.getText());
            ps.setString(2, txtAddress.getText());
            ps.setString(3, fType);
            ps.setDouble(4, Area);
            ps.setDouble(5, Total);
            ps.execute();
            JOptionPane.showMessageDialog(null, "Thank you for your order!");

        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            if (ps != null) {
                try {
                    ps.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
        }

    } // end newOrder

    public void orderList() {
        Statement stmt = null;
        try {
            stmt = getConnection().createStatement();
            rs = stmt.executeQuery("SELECT * from CustomerOrders");
            ResultSetMetaData md = rs.getMetaData();
            int columns = md.getColumnCount();
            while (rs.next()) {
                for (int i = 1; i < columns; i++) {
                    txtCustomer.setText(rs.getString(i) + " ");
                    System.out.print(rs.getString(i) + " ");
                    System.out.println();

                } // end for

            }// end while
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            if (stmt != null) {
                try {
                    stmt.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
        }
    } // end orderList

} // end class