Server Sockets

A client socket dials out. A server socket sits and waits. The previous lesson built clients that opened a TCP connection to some address and port. This lesson flips the direction and shows how a Java program becomes the thing on the other end: a process that binds to a port, accepts incoming connections, and serves each client. The path starts with the simplest possible server, sees why it cannot handle more than one customer at a time, and grows it into something that can handle thousands.

The running example is an "order status" server for an online store. A client sends an order ID, and the server replies with PLACED, SHIPPED, or DELIVERED. We will build it three times: single-threaded, thread-per-client, and pool-backed. Each rewrite fixes a real problem.