Topic: Java Inter-App Communication 101

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II. Java Language Networking Features

A. Sockets and ServerSockets

Server App constructs ServerSocket and sets it in listening mode.
When a client connects, ServerSocket returns a client socket to manage this conversation.



   // Server code
   java.net.ServerSocket server = new java.net.serversocket( 1789 );
   java.net.Socket client = server.accept(); // normally blocks

B. Addresses

Server sockets run “locally”, thus aren't constructed with IP address.
They do require a port (Unix - above 1024 for non-root processes).
Client sockets require an IP address and port - this couplet defines a socket.
Connecting on the same machine - use IP address localhost.




     // Client code – localhost
   java.net.Socket client = new java.net.Socket( “localhost”, 1789 );

C. Streams

Following the Unix model, socket I/O is similar to other Java I/O.
Client sockets use InputStream and OutputStream objects for communication.
The flush() method is important in network I/O.




     // Client code
   OutputStream out = client.getOutputStream();
   out.write( . . . );
   out.flush(); // flush

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