Thread: socket connection - moving from a single client to multiple clients

I have a socket connection: server - single client working fine

I wish to add some extra clients

Each client runs on a separate PC on the same network

All PCs have a large similar java main program BUT the server PC is the only PC which initiates a trade

When looking at examples on the net, most servers are closed after receiving a particular message from a client

My clients send a single message to the server

Supposedly I can put a counter in the server code and once it reaches the number of clients I have, I can close the server

In the main java program on the server PC I come to a point in the code where I need to wait until all clients have sent their respective messages

I am unsure how to do this or even if this is possible ?

Am seeking a simple solution

Bob M