In this tutorial, we'll only explain how to write the second kind of extension: an editor displaying a dialog box letting the user set or change the value of the XHTML bgcolor attribute. This attribute is defined by the XHTML 1.0 Transitional DTD for the following elements: body, table, tr, th, td. The modal dialog box displayed by this attribute editor is a standard javax.swing.JColorChooser.

A custom attribute editor implements interface SetAttribute.EditorFactory which is a factory class creating modal dialog boxes.

Excerpts from HexColorChooser.java:

public class HexColorChooser implements SetAttribute.EditorFactory {
    public SetAttribute.Editor createEditor(Component parentComponent, 
                                            Element element, Name attributeName,
                                            DataType attributeType) {
        return new Chooser(parentComponent,
                           dialogTitle(element, attributeName));
    }

The above method is passed information identifying the attribute to be edited: element, attributeName, attributeType.

The modal dialog box created and returned by the above methods must implement interface SetAttribute.Editor.

private static class Chooser implements SetAttribute.Editor {
    public final Component parentComponent;
    public final String title;

    public Chooser(Component parentComponent, String title) {
        this.parentComponent = parentComponent;
        this.title = title;
    }

    public String editAttributeValue(String attributeValue) {
        Color color = fromHexString(attributeValue.trim());
        if (color == null) {
            color = Color.black;
        }

        color = JColorChooser.showDialog(parentComponent, title, color);
        if (color == null) {
            return null;
        }

        return toHexString(color);
    }
}