Redirecting System.out to JTextPane

Question

I have a class (shown below) that extends JPanel and contains a JTextPane. I want to redirect System.out and System.err to my JTextPane. My class does not seem to work. When I run it, it does redirect the system prints, but they do not print to my JTextPane. Please help!

Note: The calls are only redirected when the application launches. But any time after launch, the System.out calls are not redirected to the JTextPane. (ie, if I place a System.out.prinln(); in the class, it will be called, but if it is placed in a actionListener for later use, it does not redirect).

public class OSXConsole extends JPanel {
    public static final long serialVersionUID = 21362469L;

    private JTextPane textPane;
    private PipedOutputStream pipeOut;
    private PipedInputStream pipeIn;


    public OSXConsole() {
        super(new BorderLayout());
        textPane = new JTextPane();
        this.add(textPane, BorderLayout.CENTER);

        redirectSystemStreams();

        textPane.setBackground(Color.GRAY);
        textPane.setBorder(new EmptyBorder(5, 5, 5, 5));

    }


    private void updateTextPane(final String text) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                Document doc = textPane.getDocument();
                try {
                    doc.insertString(doc.getLength(), text, null);
                } catch (BadLocationException e) {
                    throw new RuntimeException(e);
                }
                textPane.setCaretPosition(doc.getLength() - 1);
            }
        });
    }


    private void redirectSystemStreams() {
      OutputStream out = new OutputStream() {
        @Override
        public void write(final int b) throws IOException {
          updateTextPane(String.valueOf((char) b));
        }

        @Override
        public void write(byte[] b, int off, int len) throws IOException {
          updateTextPane(new String(b, off, len));
        }

        @Override
        public void write(byte[] b) throws IOException {
          write(b, 0, b.length);
        }
      };

      System.setOut(new PrintStream(out, true));
      System.setErr(new PrintStream(out, true));
    }


}

Answer 1

Piped streams always confuse me, which is why my Message Console solution doesn't use them. Anyway here is my attempt at a console using piped streams. A couple of differences:

a) it uses a JTextArea because a JTextArea is more efficient than a JTextPane for just displaying text. Of course if you intend to add attributes to the text then you need a text pane.

b) this solution uses Threads. I'm sure I read somewhere that this was necessary to prevent blocking of the output. Anyway it works in my simple test case.

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

public class Console implements Runnable
{
    JTextArea displayPane;
    BufferedReader reader;

    private Console(JTextArea displayPane, PipedOutputStream pos)
    {
        this.displayPane = displayPane;

        try
        {
            PipedInputStream pis = new PipedInputStream( pos );
            reader = new BufferedReader( new InputStreamReader(pis) );
        }
        catch(IOException e) {}
    }

    public void run()
    {
        String line = null;

        try
        {
            while ((line = reader.readLine()) != null)
            {
//              displayPane.replaceSelection( line + "\n" );
                displayPane.append( line + "\n" );
                displayPane.setCaretPosition( displayPane.getDocument().getLength() );
            }

            System.err.println("im here");
        }
        catch (IOException ioe)
        {
            JOptionPane.showMessageDialog(null,
                "Error redirecting output : "+ioe.getMessage());
        }
    }

    public static void redirectOutput(JTextArea displayPane)
    {
        Console.redirectOut(displayPane);
        Console.redirectErr(displayPane);
    }

    public static void redirectOut(JTextArea displayPane)
    {
        PipedOutputStream pos = new PipedOutputStream();
        System.setOut( new PrintStream(pos, true) );

        Console console = new Console(displayPane, pos);
        new Thread(console).start();
    }

    public static void redirectErr(JTextArea displayPane)
    {
        PipedOutputStream pos = new PipedOutputStream();
        System.setErr( new PrintStream(pos, true) );

        Console console = new Console(displayPane, pos);
        new Thread(console).start();
    }

    public static void main(String[] args)
    {
        JTextArea textArea = new JTextArea();
        JScrollPane scrollPane = new JScrollPane( textArea );

        JFrame frame = new JFrame("Redirect Output");
        frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
        frame.getContentPane().add( scrollPane );
        frame.setSize(200, 100);
        frame.setVisible(true);

        Console.redirectOutput( textArea );
        final int i = 0;

        Timer timer = new Timer(1000, new ActionListener()
        {
            public void actionPerformed(ActionEvent e)
            {
                System.out.println( new java.util.Date().toString() );
                System.err.println( System.currentTimeMillis() );
            }
        });
        timer.start();
    }
}