Implementing a Console Window with a JTextArea Component
This example creates a console window using a JTextArea which
shows all output printed to System.out and System.err.
System.out and System.err are replaced with piped io
streams. Two reader threads are created that retrieve the output from
these piped io streams and append it to the JTextArea component.
The console window is created using
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.text.*;
public class Console extends JFrame {
PipedInputStream piOut;
PipedInputStream piErr;
PipedOutputStream poOut;
PipedOutputStream poErr;
JTextArea textArea = new JTextArea();
public Console() throws IOException {
// Set up System.out
piOut = new PipedInputStream();
poOut = new PipedOutputStream(piOut);
System.setOut(new PrintStream(poOut, true));
// Set up System.err
piErr = new PipedInputStream();
poErr = new PipedOutputStream(piErr);
System.setErr(new PrintStream(poErr, true));
// Add a scrolling text area
textArea.setEditable(false);
textArea.setRows(20);
textArea.setColumns(50);
getContentPane().add(new JScrollPane(textArea), BorderLayout.CENTER);
pack();
setVisible(true);
// Create reader threads
new ReaderThread(piOut).start();
new ReaderThread(piErr).start();
}
class ReaderThread extends Thread {
PipedInputStream pi;
ReaderThread(PipedInputStream pi) {
this.pi = pi;
}
public void run() {
final byte[] buf = new byte[1024];
try {
while (true) {
final int len = pi.read(buf);
if (len == -1) {
break;
}
SwingUtilities.invokeLater(new Runnable() {
public void run() {
textArea.append(new String(buf, 0, len));
// Make sure the last line is always visible
textArea.setCaretPosition(textArea.getDocument().getLength());
// Keep the text area down to a certain character size
int idealSize = 1000;
int maxExcess = 500;
int excess = textArea.getDocument().getLength() - idealSize;
if (excess >= maxExcess) {
textArea.replaceRange("", 0, excess);
}
}
});
}
} catch (IOException e) {
}
}
}
}
try {
new Console();
} catch (IOException e) {
}
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