Caching URL contents

Question

I have a program that needs to download several large Jar files that contain resources. It would be nice if these could be cached locally so that I don't have to keep hitting my server. My Apache server is setting Expires info on my files to be 2 months after the access time, but no matter how many times I hit my server, I get a 200 OK message returned instead of a 304 Not Modified.
I intend to eventually use this in a WebStart application. Can I have Java cache these files locally and only update them if the timestamp on the server changes? Without violating my sandbox?
Mark McKay
import java.net.*;
import java.util.*;
* @author kitfox
public class URLTestMain
/** Creates a new instance of NewMain */
public URLTestMain()
* @param args the command line arguments
public static void main(String[] args)
try
URL url = new URL("http://www.kitfox.com/text/text.html");
URLConnection conn = url.openConnection();
System.err.println(conn.toString());
System.err.printf("Content Encoding %s, Content length %d, Content type %s, Default use caches %b, Expiration %d, If ModifiedSince %d, Last MOdified %d, Use Caches %b\n\n",
conn.getContentEncoding(), conn.getContentLength(), conn.getContentType(), conn.getDefaultUseCaches(),
conn.getExpiration(), conn.getIfModifiedSince(), conn.getLastModified(), conn.getUseCaches()
Map<String, List<String>> headers;
System.err.println("Header Fields");
headers = conn.getHeaderFields();
for (String key: headers.keySet())
List<String> list = headers.get(key);
System.err.printf("Header '%s'\n", list);
for (String ele: list)
System.err.println("\t" + ele);
//Download file
Object obj = conn.getContent();
catch (Exception e)
e.printStackTrace();
}

Answer 1

Check the http documentation re: request headers. I've got a feeling there's a header or similar which says "only retrieve this document if modified".