The java.net package includes classes and interfaces that help manage cookies and can be used to create a stateful (as opposed to stateless) HTTP session. The classes are CookieHandler, CookieManager, and HttpCookie. The interfaces are CookiePolicy and CookieStore. The creation of a stateful HTTP session is beyond the scope of this book.
TCP/IP Server Sockets
As mentioned earlier, Java has a different socket class that must be used for creating server applications. The ServerSocket class is used to create servers that listen for either local or remote client programs to connect to them on published ports. ServerSockets are quite different from normal Sockets. When you create a ServerSocket, it will register itself with the system as having an interest in client connections. The constructors for ServerSocket reflect the port number that you want to accept connections on and, optionally, how long you want the queue for said port to be. The queue length tells the system how many client connections it can leave pending before it should simply refuse connections. The default is 50. The constructors might throw an IOException under adverse conditions. Here are three of its constructors:
ServerSocket has a method called accept( ), which is a blocking call that will wait for a client to initiate communications and then return with a normal Socket that is then used for communication with the client.