In many cases if you are looking for some example code showing how to achieve a particular task with Jiffie your best starting point will be the source code for the JUnit tests distributed with Jiffie. You'll find this source in the files whose namea end in Test.java. One of the goals of the unit tests are to exercise Jiffie functionality thoroughly, so you are likely to find many common use cases already implemented. If you can't find what you need, have a look at the mailing list archives, and if you are still in the dark, send a message to the list.
It may be possible, but I haven't attempted it, and nobody has posted any example code which does this. You may want to have a look at the Jacob Project mailing list to see if other people have attempted this. Alternatively the JDIC project have implemented similar functionality.
This is a known issue with Jiffie. What appears to be happening is that when the size method of the list is called, the length attribute of the underlying ElementList object is being retrieved. Normally this should return a Variant representing an integer, but where an element exists in the list with the name "length", a Variant representing this list member itself is returned rather than the integer list size. The only workaround at present is to rename the element named "length" in the HTML document. (Thanks to Christian Hargraves for reporting this).