How to use java as a backend?

[gpraveen]

Yesterday, for the first time, i heard that java can be used as a backend. But i have no idea how it is possible.
Can any one help me in explaining the concept behind it and what are the components needed for it.
Thank you !!

[Fou-Lu]

What specifically do you mean? A desktop environment or a web environment?
Java itself is just a language; you can create the backend set up with all the processing in the application. You can then build a front end gui within the same application, or use a different application to generate the front end and link to the 'back end' application using a simple import, RMI, soap services etc etc. There are a number of ways to separate the front from the back end.

[gpraveen]

What is difference in using as a desktop environment and a web environment?
How can it be used in both?

[Fou-Lu]

Java can be run via a server software such as tomcat, or run infinitely as a service. All that would do is provide you with a means to access it remotely via RMI, SOAP or using JSP in a server side environment. It is literally just an application run on the server and talked to by a remote client.
Desktop environment by itself would simply be a program that runs solely on your machine. It may or may not be separated into different levels of processing (n-tier, client -> business (backend)). Running on a remote location works the same, just the protocols for communication will change.