java - JScrollPane 和 JTextArea 滚动

Question

我正在将一些日志输出到 JScrollPane 中包含的 JTextArea 中，但是当输出到达 textArea 底部时，自动滚动功能不起作用。我尝试了网上看到的几种方法，但都没有效果。以下是到目前为止我的部分代码。

JTextArea ouputLogPane = new JTextArea();
JScrollPane outputPane = new JScrollPane(ouputLogPane);
outputPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
outputPane.setBounds(75, 501, 746, 108);
contentPane.add(outputPane);

现在，我在另一个类(class)中正在读取源文件，并使用下面的代码将日志详细信息附加到 textArea。

public void readFile(JTextArea outputLog, JScrollPane scrollPane){
    count = 0;
    while(moreLinesToRead){
       if(count % 100 == 0){
       outputLog.update(outputLog.getGraphics());
       outputLog.append("Completed Reading"+ count + " Records "\n");
       DefaultCaret caret = (DefaultCaret)outputLog.getCaret();
       caret.setUpdatePolicy(DefaultCaret.ALWAYS_UPDATE);
       outputLog.update(outputLog.getGraphics());
       //tried the one below but did not work either
       //outputLog.setCaretPosition(outputLog.getDocument().getLength());
    }
    count++;
    }
}

最后，我在单击按钮时调用此方法，如下所示。

JButton btnNewButton = new JButton("Start Reading");
    btnNewButton.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
        migrationUtil.readFile(ouputLogPane,outputPane);
    }
});

所以基本上只有在执行完成后才会打印完整的输出。我读到我可能必须使用单独的线程来处理它，但不太确定如何继续。

编辑

import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.sql.Connection;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.border.LineBorder;
import javax.swing.border.TitledBorder;

public class ReadingExample extends JFrame {

    private JPanel contentPane;


    private Connection conn;


    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    ReadingExample frame = new ReadingExample();
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the frame.
     */
    public ReadingExample() {
        //setResizable(false);
        setFont(new Font("Dialog", Font.BOLD, 13));
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 936, 720);
        setLocationRelativeTo(null);
        contentPane = new JPanel();
        contentPane.setBorder(new LineBorder(new Color(0, 0, 0), 2));
        setContentPane(contentPane);
        contentPane.setLayout(null);

        final JTextArea ouputLogPane = new JTextArea();
        final JScrollPane outputPane = new JScrollPane(ouputLogPane);
        //outputPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
        outputPane.setBounds(67, 189, 746, 108);
        contentPane.add(outputPane);


        JButton btnNewButton = new JButton("Start Reading");
        btnNewButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                File file = new File("file.txt");
                FileReader fileReader = null;
                try {
                    fileReader = new FileReader(file);
                } catch (FileNotFoundException e1) {
                    // TODO Auto-generated catch block
                    e1.printStackTrace();
                }
                BufferedReader bufferedReader = new BufferedReader(fileReader);

                String line;
                try {
                    while((line = bufferedReader.readLine()) != null) {
                        ouputLogPane.append(line + "\n");
                        ouputLogPane.setCaretPosition(ouputLogPane.getDocument().getLength());
                        try {
                            Thread.sleep(200);
                        } catch (InterruptedException ee) {
                            ee.printStackTrace();
                        }
                    }
                } catch (IOException e1) {
                    // TODO Auto-generated catch block
                    e1.printStackTrace();
                }

            }
        });
        btnNewButton.setFont(new Font("Tahoma", Font.BOLD, 14));
        btnNewButton.setBounds(358, 620, 167, 29);
        contentPane.add(btnNewButton);

        //JPanel panel_3 = new JPanel();
        //panel_3.setBorder(new TitledBorder(null, "Process Log", TitledBorder.LEADING, TitledBorder.TOP, null, null));
        //panel_3.setBounds(57, 173, 769, 132);
        //contentPane.add(panel_3);

    }
}

Answer 1

您想要做的是在单独的线程中读取该文件，这样您的 Swing 线程就不会被它阻塞，从而允许您同时更新文本区域。

但是，您仍然需要更新 Swing 线程上的 GUI，因此您可以通过调用 SwingUtilities.invokeLater(runnable) 来完成此操作。

这是一个工作示例(请注意，我添加了 Thread.sleep(200)，以便您可以看到它正在更新):

import javax.swing.*;
import java.awt.*;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;

public class ReadingExample {

    public static void main(String[] args) {

        JFrame jFrame = new JFrame();
        jFrame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        jFrame.setLocationRelativeTo(null);

        JPanel mainPanel = new JPanel(new BorderLayout());

        JTextArea jTextArea = new JTextArea();

        JScrollPane scrollPane = new JScrollPane(jTextArea);
        scrollPane.setPreferredSize(new Dimension(300, 300));
        mainPanel.add(scrollPane, BorderLayout.CENTER);

        JButton btnNewButton = new JButton("Start Reading");
        mainPanel.add(btnNewButton, BorderLayout.SOUTH);

        jFrame.setContentPane(mainPanel);

        jFrame.pack();
        jFrame.setVisible(true);

        btnNewButton.addActionListener(e -> {

            new Thread(() -> {

                File file = new File("file.txt");

                try (FileReader fileReader = new FileReader(file);
                     BufferedReader bufferedReader = new BufferedReader(fileReader)) {

                    String line;
                    while((line = bufferedReader.readLine()) != null) {

                        final String fLine = line;

                        SwingUtilities.invokeLater(() -> {
                            jTextArea.append(fLine + "\n");
                            jTextArea.setCaretPosition(jTextArea.getDocument().getLength());
                        });

                        Thread.sleep(200);
                    }

                } catch (Exception e1) {
                    e1.printStackTrace();
                }

            }).start();
        });
    }
}