Xml syntax highlighting in Swing JTextPane

This code is published as an open source project on https://github.com/kdekooter/xml-text-editor/

Description
A subclass of JTextPane that uses regular expressions for syntax highlighting.

First we extend JTextPane:

public class XmlTextPane extends JTextPane {

    private static final long serialVersionUID = 6270183148379328084L;

    public XmlTextPane() {

        // Set editor kit
        this.setEditorKitForContentType("text/xml", new XmlEditorKit());
        this.setContentType("text/xml");
    }

}

Next we define a custom EditorKit:

public class XmlEditorKit extends StyledEditorKit {

    private static final long serialVersionUID = 2969169649596107757L;
    private ViewFactory xmlViewFactory;

    public XmlEditorKit() {
        xmlViewFactory = new XmlViewFactory();
    }

    @Override
    public ViewFactory getViewFactory() {
        return xmlViewFactory;
    }

    @Override
    public String getContentType() {
        return "text/xml";
    }
}

The EditorKit needs a ViewFactory:

public class XmlViewFactory extends Object implements ViewFactory {

    /**
     * @see javax.swing.text.ViewFactory#create(javax.swing.text.Element)
     */
    public View create(Element element) {

        return new XmlView(element);
    }

}

Finally we create the syntax highlighting view:

package nl.boplicity.swing.text;

import java.awt.Color;
import java.awt.Graphics;
import java.util.HashMap;
import java.util.Map;
import java.util.SortedMap;
import java.util.TreeMap;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import javax.swing.text.BadLocationException;
import javax.swing.text.Document;
import javax.swing.text.Element;
import javax.swing.text.PlainDocument;
import javax.swing.text.PlainView;
import javax.swing.text.Segment;
import javax.swing.text.Utilities;

/**
 * Thanks: http://groups.google.com/group/de.comp.lang.java/msg/2bbeb016abad270
 * 
 * IMPORTANT NOTE: regex should contain 1 group.
 * 
 * Using PlainView here because we don't want line wrapping to occur.
 * 
 * @author kees
 * @date 13-jan-2006
 *
 */
public class XmlView extends PlainView {

    private static HashMap<Pattern, Color> patternColors;
    private static String TAG_PATTERN = "(</?[a-z]*)\\s?>?";
    private static String TAG_END_PATTERN = "(/>)";
    private static String TAG_ATTRIBUTE_PATTERN = "\\s(\\w*)\\=";
    private static String TAG_ATTRIBUTE_VALUE = "[a-z-]*\\=(\"[^\"]*\")";
    private static String TAG_COMMENT = "(<!--.*-->)";
    private static String TAG_CDATA_START = "(\\<!\\[CDATA\\[).*";
    private static String TAG_CDATA_END = ".*(]]>)";

    static {
        // NOTE: the order is important!
        patternColors = new HashMap<Pattern, Color>();
        patternColors.put(Pattern.compile(TAG_CDATA_START), new Color(128, 128, 128));
        patternColors.put(Pattern.compile(TAG_CDATA_END), new Color(128, 128, 128));
        patternColors
                .put(Pattern.compile(TAG_PATTERN), new Color(63, 127, 127));
        patternColors.put(Pattern.compile(TAG_ATTRIBUTE_PATTERN), new Color(
                127, 0, 127));
        patternColors.put(Pattern.compile(TAG_END_PATTERN), new Color(63, 127,
                127));
        patternColors.put(Pattern.compile(TAG_ATTRIBUTE_VALUE), new Color(42,
                0, 255));
        patternColors.put(Pattern.compile(TAG_COMMENT), new Color(63, 95, 191));
    }

    public XmlView(Element element) {

        super(element);

        // Set tabsize to 4 (instead of the default 8)
        getDocument().putProperty(PlainDocument.tabSizeAttribute, 4);
    }

    @Override
    protected int drawUnselectedText(Graphics graphics, int x, int y, int p0,
            int p1) throws BadLocationException {

        Document doc = getDocument();
        String text = doc.getText(p0, p1 - p0);

        Segment segment = getLineBuffer();

        SortedMap<Integer, Integer> startMap = new TreeMap<Integer, Integer>();
        SortedMap<Integer, Color> colorMap = new TreeMap<Integer, Color>();

        // Match all regexes on this snippet, store positions
        for (Map.Entry<Pattern, Color> entry : patternColors.entrySet()) {

            Matcher matcher = entry.getKey().matcher(text);

            while (matcher.find()) {
                startMap.put(matcher.start(1), matcher.end());
                colorMap.put(matcher.start(1), entry.getValue());
            }
        }

        // TODO: check the map for overlapping parts

        int i = 0;

        // Colour the parts
        for (Map.Entry<Integer, Integer> entry : startMap.entrySet()) {
            int start = entry.getKey();
            int end = entry.getValue();

            if (i < start) {
                graphics.setColor(Color.black);
                doc.getText(p0 + i, start - i, segment);
                x = Utilities.drawTabbedText(segment, x, y, graphics, this, i);
            }

            graphics.setColor(colorMap.get(start));
            i = end;
            doc.getText(p0 + start, i - start, segment);
            x = Utilities.drawTabbedText(segment, x, y, graphics, this, start);
        }

        // Paint possible remaining text black
        if (i < text.length()) {
            graphics.setColor(Color.black);
            doc.getText(p0 + i, text.length() - i, segment);
            x = Utilities.drawTabbedText(segment, x, y, graphics, this, i);
        }

        return x;
    }

}