Implementing a Console Window with a JTextArea Component - Java Swing

Java examples for Swing:JTextArea

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Description

Implementing a Console Window with a JTextArea Component

Demo Code

import java.awt.BorderLayout;
import java.io.IOException;
import java.io.PipedInputStream;
import java.io.PipedOutputStream;
import java.io.PrintStream;

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

class Console extends JFrame {
  PipedInputStream piOut;/* w  ww  .java2  s.  c o  m*/
  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) {
      }
    }
  }
}

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