テキストエリアへのエラー文の出力

import java.io.ByteArrayOutputStream;
import java.io.PrintStream;
import javax.swing.JTextPane;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.Document;

public class TextPanePrintStream extends PrintStream {

	public TextPanePrintStream(JTextPane target, AttributeSet as) {
		super(new TextPaneOutputStream(target, as));
	}

	public TextPanePrintStream(JTextPane target) {
		super(new TextPaneOutputStream(target, target.getCharacterAttributes()));
	}
 
	public AttributeSet getAttributeSet() {
		TextPaneOutputStream os = (TextPaneOutputStream)out;
		return os.getAttributeSet();
	}

	public void setAttributeSet(AttributeSet as) {
		TextPaneOutputStream os = (TextPaneOutputStream)out;
		os.setAttributeSet(as);
	}
}

class TextPaneOutputStream extends ByteArrayOutputStream {

	private final JTextPane target;
	private AttributeSet attributeSet;

	TextPaneOutputStream(JTextPane target, AttributeSet as) {
		super();
		this.target = target;
		setAttributeSet(as);
	}

	public void write(byte[] b, int off, int len) {
		String s = new String(b, off, len);
		Document doc = target.getDocument();
		try {
			doc.insertString(doc.getLength(), s, attributeSet);
		} catch (BadLocationException e) {
			throw new RuntimeException(e);
		}
	}

	AttributeSet getAttributeSet() {
		return attributeSet.copyAttributes();
	}

	void setAttributeSet(AttributeSet as) {
		this.attributeSet = as.copyAttributes();
	}
}