Java Cookbook, 1st Edition

Chapter 14. Network Clients

14.0 Introduction

Java can be used to write many types of networked programs. In traditional socket-based code, the programmer is responsible for structuring the interaction between the client and server; the TCP socket code simply ensures that whatever data you send gets to the other end. In higher-level types, such as HTTP, RMI, CORBA, and EJB, the software takes over more control. Sockets are often used for connecting to legacy servers; if you were writing a new application from scratch, you’d be better off using a higher-level service.

It may be helpful to compare sockets with the telephone system. Telephones were originally used for analog voice traffic, which is pretty unstructured. Then they began to be used for some layered applications; the first widely popular one was facsimile transmission, or fax. Where would fax have been without the widespread availability of voice telephony? The second wildly popular layered application historically was dial-up TCP/IP. This coexisted with the web to become popular as a mass-market service. Where would dial-up IP be without widely deployed voice lines? And where would the internet be without dial-up IP? Fax and dial-up are mostly gone now, but they paved the way for your smartphone’s networked ability, which is what makes it useful (and even seductive as a time sink).

Sockets are layered like that too. The web, RMI, JDBC, CORBA, and EJB are all layered on top of sockets. HTTP is now the most common protocol ...