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Once and for all, is there a way to go through firewalls with rmi callbacks to client?
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Posted By:   Hugues_Rousseau
Posted On:   Thursday, April 12, 2001 06:43 AM

Most answers so far tell me it is not possible. Some people seem to have tried working workarounds, but those sound more like legends than actual real-life solutions. In a live environment, is it possible for a server to make a rmi callback to a client applet through a firewall, and how? If not, how can a system like Cisco collaborative tools achieve asynchronous event handling from client to client through a server reliably? There has got to be a way! Thank you.

Re: Once and for all, is there a way to go through firewalls with rmi callbacks to client?

Posted By:   Anonymous  
Posted On:   Monday, December 6, 2004 01:31 PM

i'm also looking for an answer to thus question. Hope there is one in almost 4 years?

Re: Once and for all, is there a way to go through firewalls with rmi callbacks to client?

Posted By:   Tim_Taylor  
Posted On:   Sunday, December 23, 2001 10:59 AM

You can't do it using pure RMI callbacks in the general case of multiple firewalls. That's reasonably certain. The only thing the Sun reference implementation provides for passing through firewalls is HTTP tunnelling and SOCKS. SOCKS will solve only a miniscule number of cases since it only helps on some client firewalls -- not the server firewall, and not all client firewalls.



HTTP tunnelling (the most useful solution) in RMI does not do callbacks. Therefore, once and for all, you can't do callbacks through firewalls to clients (in my opinion).



However you can do asynhronous communication from server to client through firewalls.



You can achieve asynchronous communication using an HTTP streaming socket from the client to a servlet on the server. This is well documented in the latest O'Reilly Java Servlets book and probably on the Web too.



You can also use JMS if your JMS provider handles HTTP tunnelling. This provides a heavier client, though.



WebLogic (alone as far as I know) provides transparent RMI callbacks in their implementation of RMI. The WebLogic runtime (as in the JMS case above) adds a lot of weight to your client, though. You can mitigate this by caching the applet using the Java Plug-In or by using WebStart.



The new RMI book called "java.rmi" speculates that Java 1.4 may solve the problem. I'm not holding my breath because I haven't seen this in black and white from Sun yet.

Re: Once and for all, is there a way to go through firewalls with rmi callbacks to client?

Posted By:   samah_badawy  
Posted On:   Monday, July 2, 2001 04:48 AM

I have the same problem , I need to do callback from the server to client applets to update client whenever a change takes place but i don't know how.

Re: Once and for all, is there a way to go through firewalls with rmi callbacks to client?

Posted By:   Luigi_Viggiano  
Posted On:   Tuesday, April 24, 2001 06:08 AM

It sounds like a hard question, I'm not sure to have understood.
I've never experimented RMI thru Firewalls, but I think it's possible: it depends on the configuration of the firewall. You must enable the firewall to accept connection on the port used by the RMI listener (and if you want, filtering ip addresses).
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