Creating a simple LAN messenger

Question

I want to create a simple LAN conference-chat style messenger in Java but I have no clue where to start.
It must have the following features:

no permanent username: the user must be able to type in a username every time he joins but should have a remember me option in case he uses it frequently

a simple chatroom interface with all the users online displayed on the right and the chat messages in the centre

a private chat service and a block option

I do not want the ready-made code, I want someone to explain to me where to start and how to go about doing it and the things I should know (like e.g. a text box to enter user name and stuff )
Just imagine it as being a messenger allowing all the employees in one building to chat with each other

Answer 1

Though your question is pretty vague you seem to have the basics (sockets and all that) in place. I suggest you start by reading the All About Sockets and All About Datagrams Java lessons on Oracle's site to get started. The main content from the second lesson you may want to digest is the part about broadcasting (for the purposes of automatic server detection).

Here's how i'd go about the implementation on a high level:

• Implement an application that contains server AND client functionality in one executable.
• When the app is started, run the server if no other server is detected (automatically or specified by the user).
• Always run the client. What this means, is that no dedicated server will be used as one of the clients acts as the server. Each client connects to the server (including the client running on the same machine as the server).

There obviously are numerous ways to make this kind of an application. I'm not saying that the way that i described is the best. It is, however, probably suitable to the use case you described, and its implementation is fairly simple.

Answer 2

Sounds like you need a server app and a client app for each user. They will communicate over sockets. The server will open a ServerSocket and the clients will create Sockets and connect to the server when they want to chat.

The server needs to be able to accept connections from clients. The server will hold all the global details, such as what chat rooms exist, who is in each etc. The basic behaviour is that when there are several people (clients) in a chat room, one client will say something, this is sent to the server over the socket. The server has a list of all the clients (sockets) who are in the chat room, and it sends the message to each of them.

Finally, you need to be aware that the server will have to be multithreaded and will probably require a new thread for each client socket that connects.

Answer 3

Since you don't tell if there's going to be a server for that purpose or not, maybe, in addition to previous responses, it will be interesting for you the next link:

http://docs.oracle.com/javase/tutorial/networking/datagrams/broadcasting.html

The block option can be implemented saving a list of IPs and ignoring the messages coming from them.

You must look into swing tutorial as well so you can see how you can create the windows, textboxes, textareas, buttons, and so on, so you can create you're interface:

http://docs.oracle.com/javase/tutorial/uiswing/

You can save the user quite easy using a properties file for example, but maybe you must start learning java from the beginning if you're making this kind of questions.