The cache_archive parameter used for Applet Caching doesn't supports Full URL,
but relative URL to the applet's codebase.
This limitation is mentioned in 'Applet Caching' document as 'Known Issue'.

  "Known Issues
   The path specified in the cache_archive must be a relative URL to
   the applet's codebase. Full URLs are not supported in cache_archive."

  http://java.sun.com/j2se/1.4.2/docs/guide/plugin/developer_guide/applet_caching.html
  http://java.sun.com/j2se/1.5.0/docs/guide/plugin/developer_guide/applet_caching.html
  http://java.sun.com/javase/6/docs/technotes/guides/plugin/developer_guide/applet_caching.html

In functional aspect, cache_archive accepts Full URL without error and it seems to work as expected.
But it is not supported as mentioned in the above document.

The customer wants to deploy jar files to different locations. (e.g. local disk, multiple servers.)
Full URL support in cache_archive parameter is required.