I have two servlets A & B. On B i intend to have a a method isAvailable() which A will call to check the status. If this method returns true then im going to pass it an object to B.
On doing a bit of reading i'm seeing a couple of options non of which im that familar with. JNDI with remote EJB , RMI or simple HTTP (not sure how youd do the last)
What do you guys think ? Any other options ?
Are your servlets running in the same application server? If so, you might like to use Spring to inject B into A so that the method can be called directly.
Even if the servlets are running in different containers, you can expose them (using Spring again) as Remote objects and similarly inject B into A (except that this will mean that the Spring container will inject a proxy for the remote object). This has zero footprint in your code (i.e. it's all defined by config files and Spring takes care of everything for you)
Why not make use of the fact that your infrastructure is already talking HTTP ?
So servlet A can perform an HTTP GET on a particular path to check a status (either sending back an object or checking an HTTP response code - this latter method seems a misuse of status codes, however), and PUT/POST an object if required. I note that you're running across multiple hosts, and this will work in your scenario.
The objects can be serialised using standard Java, or via a representation such as XML - perhaps serialised using XStream).
That would seem to me a pretty straightforward way to leverage off the infrastructure you have.
It looks like this isAvailable() method in Servlet B accesses some kind of "global" data which is stored in the Servlet. Could you extract this object to a separate Singleton which then is available for both Servlets?
There is one instance of Servlet A on a master host and many of Servlet B each on its own host with its own tomcat instances.
You can use java.net.URLConnection to programmatically fire a HTTP request. You can find here a simple tutorial.
Let A fire a HTTP request to B and have in B a servlet which listens on those requests and returns the response accordingly. This can be a simple response.getWriter().write("ok"); or so. You can even return a XML string and so on. In A you can then read this value from the InputStream of the URLConnection.