如何通过从 GUI 获取用户输入并将该用户输入存储到 java 中的数据库中来写入数据库？

Question

我最近一直在尝试通过从 GUI 获取用户输入来写入数据库，并且我想将来自 GUI 的用户输入存储在 netbeans 上的 derby 数据库中。 目前，我有一些代码，但它似乎不起作用，因为当我运行 GUI 并开始输入应该存储在数据库中我的程序后端的数据时，它不存储那个在 GUI 中输入的数据。 它不会将任何数据加载到数据库中！

这是写入数据库的代码：

import java.sql.Connection;
import java.sql.DatabaseMetaData;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
/**
 *
 * @author Hammad
 */
public class WritePlayerDB 
{
    private final DBConnection dbc;
    private final Connection conn;
    private Statement stmt;
    String insertQuery;
    
    public WritePlayerDB() 
    {
        dbc = new DBConnection();
        conn = dbc.getConnection();
    }
    
    public void writeToPlayerDB()
    {
        try {
            int playerID = 0;
            insertQuery = "INSERT INTO 'PLAYERINFO' ('PLAYER_ID', 'PLAYER_NAME', 'PRIZE_WON', 'CORRECT_ANSWERS')" + "VALUES(1,2,3,4)";
            this.stmt = conn.createStatement();
            this.checkExistedTable("PLAYERS");
            PreparedStatement ps = conn.prepareStatement(insertQuery);
            
            CorrectAnswers.correctAnswers[MillionaireGui.moneyCounter] = PrizeMoney.prizeLadder[MillionaireGui.moneyCounter];
            
            ps.setInt(1, playerID++);
            ps.setString(2, MillionaireGui.nameField.getText());
            ps.setInt(3, PrizeMoney.prizeLadder[MillionaireGui.moneyCounter]);
            ps.setInt(4, CorrectAnswers.correctAnswers[MillionaireGui.moneyCounter]);
            ps.executeUpdate();
            
            ps.close();
        } 
        catch (SQLException ex) 
        {
            System.out.println(ex.getMessage());
        }
    }
    
    public void checkExistedTable(String name) 
    {
        try {
            DatabaseMetaData dbmd = this.conn.getMetaData();
            String[] types = {"TABLE"};
            stmt = this.conn.createStatement();
            ResultSet rs = dbmd.getTables(null, null, null, types);

            while (rs.next()) {
                String table_name = rs.getString("TABLE_NAME");
                System.out.println(table_name);
                if (table_name.equalsIgnoreCase(name)) {
                    stmt.executeUpdate("Drop table " + name);
                    System.out.println("Table " + name + " has been deleted.");
                    break;
                }
            }
            rs.close();
        } catch (SQLException ex) {
            System.out.println(ex.getMessage());
        }
    }
}

我正在为我的 GUI 的 JTextField 调用 actionListener 中的writeToPlayerDB()方法，如下所示：

nameField.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent e)
            {
                if (nameField.getText().equals(""))
                {
                    blankName.setVisible(true);
                    blankName.setText("PLEASE DON'T LEAVE NAME BLANK");
                }
                else
                {
                    playerName.setPlayerName(nameField.getText().toUpperCase());
                    WritePlayerDB wdb = new WritePlayerDB();
                    wdb.writeToPlayerDB();
                    blankNamePanel.setVisible(false);
                    introRuleScreen();
                }
            }
        });

如果我能帮上忙，我将不胜感激，因为我已经坚持了很长时间！

Answer 1

没有足够的信息来真正了解您的核心问题是什么，但是...

static不是一个好主意，尤其是当您处理 UI 元素时，因为您可能有多个 UI 实例，然后您无法再确定您实际引用的元素实例。 最好利用依赖注入并将信息直接传递给方法。

+ "VALUES(1,2,3,4)"不是您使用PreparedStatement的方式，有关详细信息，请参阅使用 Prepared Statements

还...

int playerID = 0;
//...
ps.setInt(1, playerID++);

表示玩家 id 始终为0 （ ++是后缀操作；首先赋值，然后添加）。 事实上，您应该不惜一切代价避免手动创建这样的记录 ID，并且数据库应该在内部使用“自动递增”值。 有关详细信息，请参阅自动生成的密钥。

为简单起见，我在以下示例中使用H2 数据库引擎。 否则它应该可以与 Derby 一起使用，但您需要删除createTables方法

import java.awt.EventQueue;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.sql.*;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.StringJoiner;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JSpinner;
import javax.swing.JTextField;
import javax.swing.SpinnerNumberModel;
import javax.swing.border.EmptyBorder;

public class Main {
    public static void main(String[] args) {
        new Main();
    }

    public Main() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    DatabaseManager db = new DatabaseManager();
                    db.open();
                    JFrame frame = new JFrame();
                    frame.add(new MainPane(db));
                    frame.pack();
                    frame.setLocationRelativeTo(null);
                    frame.setVisible(true);
                } catch (SQLException ex) {
                    Logger.getLogger(Main.class.getName()).log(Level.SEVERE, null, ex);
                }
            }
        });
    }

    public class MainPane extends JPanel {

        private JTextField nameField;
        private JSpinner moneyCounter;

        public MainPane(DatabaseManager database) {
            setBorder(new EmptyBorder(32, 32, 32, 32));
            setLayout(new GridBagLayout());
            GridBagConstraints gbc = new GridBagConstraints();

            gbc.gridx = 0;
            gbc.gridy = 0;
            gbc.anchor = GridBagConstraints.LINE_END;
            gbc.insets = new Insets(4, 4, 4, 4);

            add(new JLabel("Name: "), gbc);
            gbc.gridy++;
            add(new JLabel("Counter: "), gbc);

            gbc.gridx = 1;
            gbc.gridy = 0;
            gbc.anchor = GridBagConstraints.LINE_START;

            nameField = new JTextField(10);
            moneyCounter = new JSpinner(new SpinnerNumberModel(0, 0, 100, 10));

            add(nameField, gbc);
            gbc.gridy++;
            add(moneyCounter, gbc);

            JButton btnSave = new JButton("Save");
            btnSave.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    String name = nameField.getText();
                    if (name.isBlank()) {
                        JOptionPane.showMessageDialog(MainPane.this, "Name can not be blank", "Error", JOptionPane.ERROR_MESSAGE);
                        return;
                    }
                    try {
                        int playerId = database.savePlayer(name, (int) moneyCounter.getValue());
                        List<String> results = database.getPlayerById(playerId);
                        StringJoiner sj = new StringJoiner("<br>", "<html>", "</html>");
                        for (String text : results) {
                            sj.add(text);
                        }
                        JOptionPane.showMessageDialog(MainPane.this, sj.toString(), "Success", JOptionPane.PLAIN_MESSAGE);
                    } catch (SQLException ex) {
                        ex.printStackTrace();
                        JOptionPane.showMessageDialog(MainPane.this, "Failed to create player record", "Error", JOptionPane.ERROR_MESSAGE);
                    }
                }
            });

            gbc.gridy++;
            gbc.gridx = 0;
            gbc.gridwidth = GridBagConstraints.REMAINDER;
            gbc.anchor = GridBagConstraints.CENTER;

            add(btnSave, gbc);
        }

    }

    public class DatabaseManager {

        private Connection connection;

        protected void createTables() throws SQLException {
            String cmd = "create table IF NOT EXISTS PLAYERINFO ("
                    + "PLAYER_ID bigint GENERATED BY DEFAULT AS IDENTITY(START WITH 0) PRIMARY KEY,"
                    + "PLAYER_NAME varchar(255) not null,"
                    + "PRIZE_WON int not null,"
                    + "CORRECT_ANSWERS int not null"
                    + ")";
            try (Statement stmt = connection.createStatement()) {
                stmt.execute(cmd);
            }
        }

        public void open() throws SQLException {
            if (connection != null && !connection.isClosed()) {
                try {
                    connection.close();
                } catch (SQLException ex) {
                    Logger.getLogger(Main.class.getName()).log(Level.WARNING, null, ex);
                }
            }
            connection = DriverManager.getConnection("jdbc:h2:~/test");
            createTables();
        }

        public void close() throws SQLException {
            if (connection == null) {
                return;
            }
            try {
                if (connection.isClosed()) {
                    connection = null;
                }
                connection.close();
            } finally {
                connection = null;
            }
        }

        public int savePlayer(String name, int counter) throws SQLException {
            String cmd = "insert into PLAYERINFO (PLAYER_NAME, PRIZE_WON, CORRECT_ANSWERS) values (?, ?, ?)";
            try (PreparedStatement stmt = connection.prepareStatement(cmd, Statement.RETURN_GENERATED_KEYS)) {
                Random rnd = new Random();
                stmt.setString(1, name);
                stmt.setInt(2, rnd.nextInt(100) + 1);
                stmt.setInt(3, counter);
                if (stmt.executeUpdate() != 1) {
                    throw new SQLException("Unexpectedly modified more then one row");
                }
                try (ResultSet rs = stmt.getGeneratedKeys()) {
                    if (rs.next()) {
                        return rs.getInt(1);
                    }
                }
            }

            throw new SQLException("Failed to create player record");
        }

        public List<String> getPlayerById(int id) throws SQLException {
            String cmd = "select * from playerinfo where PLAYER_ID = ?";
            List<String> results = new ArrayList<>(8);
            try (PreparedStatement stmt = connection.prepareStatement(cmd)) {
                stmt.setInt(1, id);
                try (ResultSet rs = stmt.executeQuery()) {
                    while (rs.next()) {
                        String name = rs.getString("PLAYER_NAME");
                        int prizeWon = rs.getInt("PRIZE_WON");
                        int correctAnswer = rs.getInt("CORRECT_ANSWERS");

                        results.add(name + " won " + prizeWon + " with " + correctAnswer + " correct answers");
                    }
                }
            }
            return results;
        }

    }
}