FireFox is Picky About Clipboard HTML, Java is Sloppy

Windows uses a particularly ugly format for putting HTML on the clipboard, called CF_HTML. Basically, it adds a header to the content with pretty useless information essentially declaring how many bytes in the header (and yes you have to pad the byte counts since they themselves are included in the count).

The problem between Java and Firefox is that Java always sets the ‘StartHTML’ and ‘EndHTML’ fields to -1 to indicate there is no context and Firefox will refuse to paste HTML from the clipboard if StartHTML or EndHTML is set to -1. As such, if you copy HTML from Java it will be impossible to paste into Firefox. It works perfectly with Word and IE.

I’m not 100% clear on whether the clipboard data Java is generating is valid but I consider it a bug in both Java and Firefox – Java for not being strict about what it outputs and Firefox for being too strict about what it accepts. Bug reports shall be made1{#footlink1:1285065920040.footnote}.

On the Java side, the problem is in sun.awt.windows.WDataTrasferer.HTMLSupport.convertToHTMLFormat which sadly is Sun-specific, private and loaded from the bootclasspath so a little difficult to work around. There is however a nasty, but effective, hack from Peter Buettner which does indeed get around the problem. I’ve chosen to avoid the need to copy/paste HTML in this particular application but the approach is worth saving a reference to in case it’s needed later.

1 – Bug 598289 with Mozilla and there’s a simple test case available. The bug report has also been filed with Oracle and is now available in the bug parade. ↩