Can Java do everything that CGI (PHP, Pearl...) can do?

Question

hi,
can you do everything with java, that you can do with cgi, providing that you have a server? I'm completely new to java, thats why I'd like to know this. Can you do for example a chat? Or a multiplayer game or saving and creating files (in an internet programm)?
And how (in general) does it work to write, lets say a chat. I mean the user uses his browser to go to an the URL where my java programm is. So what happens then (just the veryyyy basics to get an idea of how internet programming with java works).
thanx

Answer 1

I'm pretty sure it can do anything CGI can. I saw it used for forums and chat rooms, as well as logon-based websites and multiplayer games. I wrote a multiplayer card game with player registration, login, chat, multiple playing rooms, and money amounts saved in about a week and a half with some friends.
Java Server Pages are basically like PHP scripts, essentially outputting HTML for a web browser based on some logic, but they can use all the Java classes and language constructs and connect to databases, communicate with server applications, etc.
For an internet application, you usually need to have a server program that runs on a server machine somewhere and client applications or applets that know where to find it and connect to it. Then you can create a socket connection between the client(s) and the server (if you want multiple clients at the same time you need to use a thread for each one on the server). The socket is basically a link between the two programs that you can input and output to using standard input and output streams (use its getInputStream and getOutputStream methods). You have to decide on some sort of protocol for what the messages you send accross mean, and then write appropriate code on the server and client to handle them.