for example, In a Company named ABC have many clients. When the client requests to the webserver and he response to the client. Then the client can access some data from his account. All the data are stored in another Server. When the client can access his account, he request to the server to itsown port 1000 (store area server) and he response to the client request. then after the response the client can access and or see the all the details about it.
Client request-> Webserver --Client request-> Data Server port 1000 <-response <-Server response
Take a look at the Custom Networking trail of the Java Tutorial. It explains how to use sockets and Java IO classes to accomplish exactly this sort of thing. Of course, you mention a web server, do you want to use Servlets?