Validating XML offline: is a web-proxy and cache the solution?

Question

Is implementing a web-proxy and cache, the solution to offline XML validation?
Our application uses XML to store data (local, and remote: it's up to user), but needs to work even when offline. This is a problem for the validated XML, since it's DTD may be located on a remote server. To complicate things, we would like to allow others to extend our application with data-formats (DTD's) of their own.
At the moment, the DTD is stored in the applications jar file, but this is going to be a problem. In the data files, the URL for it's DTD includes the jar file's system dependant path name. If data files are moved to a different system (where paths are different) this will no longer work. As you can guess, simply using relative URL's (using the data file or the even the Application jar as Base URL) will also cause problems.
Before concerning ourselves with offline editing, we ran into the problem of firewalls. This we could circumvent by setting Java's global HTTP proxy (thanks to http://www.javaworld.com/javaworld/javatips/jw-javatip42.html for the tip)
  if (userNeedsProxy) {
    System.getProperties().put ("proxySet", "true");
    System.getProperties().put ("proxyHost", userProxyHost);
    System.getProperties().put ("proxyPort", userProxyPort);
  }Which appears to affect all URL.getStream() calls for http URL's, so works fine.
To get around the offline problem, I'm thinking of implementing my application as a 'proxy', and caching any downloaded DTDs locally. This cache could be seeded with our apps default DTD, and any extensions can take advantage of this as well. This solution has the benifit of not modifying the basic XML parsing routines or doing something undesirable, like just turning off validation (suggested on other forum threads). Would this involve creating a custom URLConnection object and or URLStreamHandler?
Any suggestions or comments are welcome, as I haven't started this, and I'm pretty sure it has been solved before. Does this sound feasable, or insane? :) Any experience shared is very appriciated!
Thanks in advance
...Chad

Answer 1

Hi ..
I am a computer science student .. I am reading alot about web caching
so i deside tht my graduate project must be a web caching application
but I don't know from where I must begin ... to study about creating that in java ..
can u help me plz ???
my e-mail : [email protected]
Ahmad