System.out.println to JTextArea

Question

EDIT: I have edited the post to clarify my question, now I myself, have more understanding.

I am essentially, as the title says, attempting to outpu

Answer 1

The following example creates frame with text area and redirects System.out to it:

import java.awt.BorderLayout;
import java.awt.Container;
import java.io.IOException;
import java.io.OutputStream;
import java.io.PrintStream;

import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.SwingUtilities;

public class JTextAreaOutputStream extends OutputStream
{
    private final JTextArea destination;

    public JTextAreaOutputStream (JTextArea destination)
    {
        if (destination == null)
            throw new IllegalArgumentException ("Destination is null");

        this.destination = destination;
    }

    @Override
    public void write(byte[] buffer, int offset, int length) throws IOException
    {
        final String text = new String (buffer, offset, length);
        SwingUtilities.invokeLater(new Runnable ()
            {
                @Override
                public void run() 
                {
                    destination.append (text);
                }
            });
    }

    @Override
    public void write(int b) throws IOException
    {
        write (new byte [] {(byte)b}, 0, 1);
    }

    public static void main (String[] args) throws Exception
    {
        JTextArea textArea = new JTextArea (25, 80);

        textArea.setEditable (false);

        JFrame frame = new JFrame ("stdout");
        frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
        Container contentPane = frame.getContentPane ();
        contentPane.setLayout (new BorderLayout ());
        contentPane.add (
            new JScrollPane (
                textArea, 
                JScrollPane.VERTICAL_SCROLLBAR_ALWAYS, 
                JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED),
            BorderLayout.CENTER);
        frame.pack ();
        frame.setVisible (true);

        JTextAreaOutputStream out = new JTextAreaOutputStream (textArea);
        System.setOut (new PrintStream (out));

        while (true)
        {
            System.out.println ("Current time: " + System.currentTimeMillis ());
            Thread.sleep (1000L);
        }
    }
}

Answer 2

If you want to see scrolling effect in Text Area, then instead of appending the output, you can put the new text in beginning. Example:

HttpURLConnection con = (HttpURLConnection) (new URL(url[0]).openConnection());
con.setInstanceFollowRedirects(false);
con.connect();
int responseCode = con.getResponseCode();
String location = con.getHeaderField("Location");
textArea.setText(url[0] +"," +responseCode+"," +location+"\n"+textArea.getText()); //new text is prefixed to the existing text
textArea.update(textArea.getGraphics());

Answer 3

Your error must lie somewhere else that you haven't shown us yet. Here is a very simple demo that works as expected with almost the same code as yours (I only fixed minor issues):

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.IOException;
import java.io.OutputStream;
import java.io.PrintStream;

import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.SwingUtilities;
import javax.swing.Timer;

public class TextAreaOutputStream extends OutputStream {

    private final JTextArea textArea;

    private final StringBuilder sb = new StringBuilder();

    public TextAreaOutputStream(final JTextArea textArea) {
        this.textArea = textArea;
    }

    @Override
    public void flush() {
    }

    @Override
    public void close() {
    }

    @Override
    public void write(int b) throws IOException {

        if (b == '\r') {
            return;
        }

        if (b == '\n') {
            final String text = sb.toString() + "\n";

            textArea.append(text);
            sb.setLength(0);
        } else {
            sb.append((char) b);
        }
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                JFrame frame = new JFrame(TextAreaOutputStream.class.getSimpleName());
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                JTextArea ta = new JTextArea(24, 80);
                System.setOut(new PrintStream(new TextAreaOutputStream(ta)));
                frame.add(new JScrollPane(ta));
                frame.pack();
                frame.setVisible(true);
                System.out.println("Textarea console initiated");
                Timer t = new Timer(1000, new ActionListener() {

                    int count = 1;

                    @Override
                    public void actionPerformed(ActionEvent e) {
                        System.out.println("Outputting line " + count++ + " to the console. Working properly, no?");
                    }
                });
                t.start();
            }
        });
    }
}

Answer 4

The best way to do this I have found is very simple and seems to work very nicely. I've used it for years with no issues.

JTextArea output = new JTextArea();
PrintStream out = new PrintStream(new OutputStream() {
@Override
    public void write(int b) throws IOException {
        output.append(""+(char)(b & 0xFF));
    }
});
System.setOut(out);
System.out.println("TEST");

Answer 5

You might need to use PipedOutputStream... see the answers to the question here: How to redirect all console output to a Swing JTextArea/JTextPane with the right encoding?

Basically what this does is, it redirects the System.out to a buffer, from which, the program can read the output printed with System.out. This is called Piping