Topic: Java Inter-App Communication 101

A. Background

Java is centered on the TCP/IP Networking Model.

The IP portion (Internet Protocol) defines packet structure and machine addressing.
The TCP portion (Transmission Control Protocol) adds reliable delivery, integrity, ordering.
By contrast, UDP/IP is unreliable, useful in audio, video, etc.

Within a machine, there are up to 64K Ports available.

Multiple ports allow apps like email (port 25), http(80), ftp(21), ping(7), to communicate independently.

B. Client/Server Basics

Once upon a time, Client meant desktop, and Server meant data-center machine.
With n-tiered architectures prevalent, who’s a client and who’s a server has become muddled.
- Peer-to-peer is an alternative to client/server, and not considered here.
Definition: Clients initiate connections; Servers listen for and respond to connection requests.
- Detail: Servers listen on documented port; clients connect to that port initially.
- Server then switches conversation to a different port, freeing the documented port for further connections.
Example client/server conversation: Apache web server talks to Netscape Navigator browser.