键入一个 Jtextfield 时从数据库中获取数据到 Jtextfield

Question

大家好，我有一个连接到 oracle 数据库的 Swing 应用程序，我希望它一旦我在 JTextField 中键入一个值，JFrame 上的其他 JTextfields 就会加载来自数据库的后续数据，但我没有似乎实现了这一点。我已经尝试了以下代码，但它什么也没得到。

txtNo.addKeyListener(new KeyAdapter() {
        public void keyTyped(KeyEvent ke) {
            Connection conn = null;
            try{
                Class.forName("oracle.jdbc.driver.OracleDriver");

        conn = DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:XE", "Username", "Password");
        Statement st = conn.createStatement();
        String load = "Select * from Store_info_table where PART_NUMBER = '" + txtNo.getText() + "'";
        ResultSet rs = st.executeQuery(load);
        while(rs.next()){
            txtName.setText(rs.getString("SPARE_DESC"));
        }
            }catch(Exception ae){

            }
        }
    });

Answer 1

• 将KeyListener 替换为DocumentListener
• EDT 上的数据库连接是个坏主意（太慢）。有关更多信息，请参阅 concurrency in Swing 指南
• 您容易受到 SQL 注入的攻击
• 避免使用空的catch 语句，否则您根本不知道出了什么问题。如果您不选择适当的错误处理，至少记录堆栈跟踪（仅打印它，或使用Logger）。

Answer 2

罗宾和尼克都是对的。

这是一个如何实现他们正在讨论的内容的示例......

public class TestForm02 {

    public static void main(String[] args) {
        new TestForm02();
    }

    public TestForm02() {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {

                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException ex) {
                } catch (InstantiationException ex) {
                } catch (IllegalAccessException ex) {
                } catch (UnsupportedLookAndFeelException ex) {
                }

                JFrame frame = new JFrame();
                frame.setLayout(new BorderLayout());
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new MyForm());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);

            }
        });
    }

    protected class MyForm extends JPanel {

        private JTextField txtNo;
        private JTextField txtName;
        private String partToLoad;
        private Timer loadTimer;

        public MyForm() {

            setLayout(new GridBagLayout());
            GridBagConstraints gbc = new GridBagConstraints();
            gbc.gridx = 0;
            gbc.gridy = 0;
            gbc.insets = new Insets(2, 2, 2, 2);
            gbc.anchor = GridBagConstraints.WEST;

            txtName = new JTextField(12);
            txtNo = new JTextField(12);
            txtName.setEnabled(false);

            add(new JLabel("Parts #:"), gbc);
            gbc.gridx++;
            add(txtNo, gbc);

            gbc.gridy++;
            gbc.gridx = 0;
            add(new JLabel("Description:"), gbc);
            gbc.gridx++;
            add(txtName, gbc);

            txtNo.addFocusListener(new FocusAdapter() {
                @Override
                public void focusLost(FocusEvent e) {
                    loadParts();
                }
            });

            txtNo.getDocument().addDocumentListener(new DocumentListener() {
                protected void update() {
                    loadTimer.restart();
                }

                @Override
                public void insertUpdate(DocumentEvent e) {
                    update();
                }

                @Override
                public void removeUpdate(DocumentEvent e) {
                    update();
                }

                @Override
                public void changedUpdate(DocumentEvent e) {
                    update();
                }
            });

            loadTimer = new Timer(250, new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    loadParts();
                }
            });
            loadTimer.setRepeats(false);
            loadTimer.setCoalesce(true);

        }

        protected void loadParts() {

            String text = txtNo.getText();
            // Don't want to trigger this twice...
            if (text == null ? partToLoad != null : !text.equals(partToLoad)) {
                partToLoad = text;
                txtNo.setEnabled(false);
                txtName.setEnabled(false);
                BackgroundWorker worker = new BackgroundWorker();
                worker.execute();
            }

        }

        protected class BackgroundWorker extends SwingWorker<String, String> {

            @Override
            protected String doInBackground() throws Exception {

                // Do you're database load here.  Rather then updating the text
                // field, assign it to variable and return it from here

                String desc = "Some description"; // load me :D

                // Inserted delay for simulation...
                Thread.sleep(2000);

                return desc;

            }

            @Override
            protected void done() {
                try {
                    String value = get();
                    txtName.setText(value);

                    txtName.setEnabled(true);
                    txtNo.setEnabled(true);
                } catch (InterruptedException exp) {
                    exp.printStackTrace(); // Log these some where useful
                } catch (ExecutionException exp) {
                    exp.printStackTrace(); // Log these some where useful
                }
            }
        }
    }
}

Answer 3

你知道你的数据库连接是否正常吗？例如，您可以在侦听器之外运行数据库部分并且它可以工作吗？

如果是这样，我建议改用ActionListener或FocusListener。 KeyListeners（虽然有时是必要的）通常很笨拙 - 通常有更好的方法（参见 Java Swing: Using ActionMap 和解释）：

import java.awt.event.*;
import javax.swing.*;

public class Example extends Box{

    JLabel txtName = new JLabel("Nothing Entered");

    public temp(){
        super(BoxLayout.Y_AXIS);
        // Add FocusListener to first field
        final JTextField txtNo = new JTextField(20);
        txtNo.addFocusListener(new CustomFocusListener(txtNo));
        add(txtNo);

        // Add TextListener to first field
        final JTextField txtNo2 = new JTextField(20);
        txtNo2.addFocusListener(new CustomFocusListener(txtNo2));
        add(txtNo2);

        // Add TextListener to first field
        final JTextField txtNo3 = new JTextField(20);
        txtNo3.addFocusListener(new CustomFocusListener(txtNo3));
        add(txtNo3);

        add(new JButton("Do Something"));

        add(txtName);

    }


    public static void main(String[] args){
        final JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(new Example());
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    /**
     * Your custom focust listener that does all your SQL Work
     */
    public class CustomFocusListener extends FocusAdapter{
        JTextField field;

        public CustomFocusListener(JTextField field){
            this.field = field;
        }

        @Override
        public void focusLost(FocusEvent e) {
            //Assuming your database connection works, this gives you an example to follow
            txtName.setText(field.getText());
            /*Connection conn = null;
            try{
                Class.forName("oracle.jdbc.driver.OracleDriver");

                conn = DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:XE", "Username", "Password");
                Statement st = conn.createStatement();
                String load = "Select * from Store_info_table where PART_NUMBER = '" + field.getText() + "'";
                ResultSet rs = st.executeQuery(load);
                while(rs.next()){
                   txtName.setText(rs.getString("SPARE_DESC"));
                }
            }catch(Exception ae){

            }*/
        }
    }
}

Answer 4

谢谢大家的帮助。我得到了我想要的使用 Nick 建议的 FocusListener：

 txtNo.addFocusListener(new FocusAdapter() {
        public void focusLost(FocusEvent e) {
            Connection conn = null;
            try{
                Class.forName("oracle.jdbc.driver.OracleDriver");

        conn = DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:XE", "Username", "Password");
        Statement st = conn.createStatement();
        String load = "Select * from Store_info_table where PART_NUMBER = '" + txtNo.getText().trim() + "'";
        ResultSet rs = st.executeQuery(load);
        while(rs.next()){
            txtName.setText(rs.getString("SPARE_DESC"));

        }
            }catch(Exception ae){

            }
        }
    });