joustlog

How to make the Swing HTML renderer split long words when wrapping

I spent a while today messing with JTextPane, as a sort of research for Joust Secure IM Lite's conversation window. I figured out how to insert HTML tags and text and stuff using ElementSpec objects and all sorts of fun stuff like that.

Swing's HTML renderer is cool in a lot of ways, but it does something stupid when word-wrapping: it refuses to split long words when word-wrapping. (It looks like the caption on the right.) This means that the textbox must be at least as wide as the longest word. This is not what most people want, I don't think, and it's especially inappropriate for a chat application (I think having to scroll horizontally within an IM window would be annoying).

Luckily, there's an easy, sort of hacky fix, if you're using HTMLEditorKit. (It might work with other document types, like DefaultStyledEditorKit.) You need to subclass HTMLEditorKit:
(The following code is released in the public domain.)

private static class MyEditorKit extends HTMLEditorKit {
    public ViewFactory getViewFactory() {
        return new MyViewFactory(super.getViewFactory());
    }

    private static class WordSplittingParagraphView extends ParagraphView {
        public WordSplittingParagraphView(Element elem) {
            super(elem);
        }

        protected SizeRequirements calculateMinorAxisRequirements(int axis,
                SizeRequirements r) {
            SizeRequirements sup = super.calculateMinorAxisRequirements(axis, r);
            sup.minimum = 1;
            return sup;
        }
    }

    private static class MyViewFactory implements ViewFactory {
        private final ViewFactory parent;

        public MyViewFactory(ViewFactory parent) {
            this.parent = parent;
        }

        public View create(Element elem) {
            AttributeSet attr = elem.getAttributes();
            Object name = attr.getAttribute(StyleConstants.NameAttribute);
            if (name == HTML.Tag.P || name == HTML.Tag.IMPLIED) {
                return new WordSplittingParagraphView(elem);
            }
            return parent.create(elem);
        }
    }
}

This code makes the text pane look more like the image on the right. The code provides a custom View object for paragraph elements in the HTML. The custom View object sets a minimum width of 1 pixel, where the default view would've set it to the width of the longest word in the paragraph. This allows a paragraph to be any width on the screen, regardless of how long its words are. (We're lucky that the paragraph renderer wraps correctly even if its minimum size is smaller than the longest word.)

This solution isn't perfect, and you should probably change part of it if you're going to use it in your application. Specifically, the minimum width should not be 1 pixel: unfortunately, the paragraph renderer we subclassed gets upset when its width is smaller than the first character of a line. It fights with its parent JScrollPane and ends up using 100% CPU, unless the scroll pane has a vertical scroll policy of NEVER or ALWAYS (the default is IF_NEEDED).

This problem happens because when the width is smaller than a single character, the paragraph renderer can't fit any characters on the line, and it probably wasn't written with a situation like that in mind, since by default the width is no smaller than the longest word on the line.

The solution to this is probably to go through the paragraph and find the widest character, and set the minimum width to that character's width. I haven't implemented this yet, but it shouldn't be too hard.

Posted by keith at February 22, 2004 03:39 AM | TrackBack