Firewall and URLConnection

Question

The product that am working currently has two web servers each hosting a web applicaiton. The first web server hosts the core applicaiton of the product lets call it as WEB1. And the second one is a light weight webserver developed here itself, its nothing more than a servlet/JSP container lets call this as WEB2.
The relation between these web servers is one to many i.e. For every WEB1 you have many WEB2 servers.
WEB1 calls few jsp pages from WEB2 in its jsp pages. Most of the times its frames. The upper part of the frame might serve WEB1 jsp and the lower part may serve from WEB2.
Till now we were using URLConnection object to ping the WEB2 server and if its down then convey the user that WEB2 is down. This was done
Now there are possibilities that WEB2 might reside on a machine that is not rechable by WEB2, probably behind firewall. In this case URLConnection is failing.
Is there anyway, we can bypass the firwall for pinging the WEB2 server. Rather to know the status of WEB2 from WEB1 server.
Note that the browser from which the user accesses the WEB1 server will reside on the machine where WEB2 is running.
thanks,
Vikram Patil.

Answer 1

The crux of your topic seems to be How to open URLConnection from a host A to another host B, given that there is a firewall between them ?
URLConnection uses socket(s) underneath itself.
If the requisite port (usually 80 for HTTP traffic) is opened in firewall to let the trafiic in the requisite direction go through, you should not any problem.
A commonly used configuration is to have a proxy server of sorts along with the firewall. The application opening the URLConnection would direct all HTTP requests to the proxy server. The proxy server would in turn send the HTTP requests to the target server, but only after consuming some infomation from the request which tells it about the client accessing it. And similarly for HTTP responses.
There is in-built support in HttpURLConnection implementations to use proxies. The way to have your application actually send HTTP requests through a proxy is pretty simple. It basically involes setting a couple of system properties. http.proxyHost and http.proxyPort. The HttpURLConnection implementation will do the actual dirty work for you.
For a wealth of information about this, do a search on these forums.