client-server communication with java

Implement a simple client-server mechanism according to protocol UDP..client will read messages from keyboard, then he will send them to server and server will forward the messages to all registered clients.. the messages which client sends to server will have the below form: a) Signin <username> b) Message <message> c) Signout Server according to a,b or c will do these: for a)he will store the address and <username> with which the user signed in..he will store these in a list which keeps the registered users.. then he will inform the new user for his successful record and also the rest of users for his entry for b)he will send the message to all registered users except the one who sent it for c)he will delete the user from the list of active users and will inform the rest of them for his withdrawal IMPORTANT: define specific ports to which server and clients will listen communication will be two-way..that means that client and server will receive and send messages and one of these processes must be done in a new thread also if a client is already in the list the program must not add him if we try to do this CODE IS INCLUDED BUT NEED SOME EXTRA TO ADD