Java Web Services: Up and Running, 2nd Edition

What Is REST?

Roy Fielding coined the acronym REST in his PhD dissertation. Chapter 5 of Fielding’s dissertation lays out the guiding principles for what have come to be known as REST-style or RESTful web services. Fielding has an impressive résumé. He is, among other things, a principal author of the HTTP 1.1 specification and a cofounder of the Apache Software Foundation.

REST and SOAP are quite different. SOAP is a messaging protocol in which the messages are XML documents, whereas REST is a style of software architecture for distributed hypermedia systems, or systems in which text, graphics, audio, and other media are stored across a network and interconnected through hyperlinks. The World Wide Web is the obvious example of such a system. As the focus here is on web services, the World Wide Web is the distributed hypermedia system of interest. In the Web, HTTP is both a transport protocol and a messaging system because HTTP requests and responses are messages. The payloads of HTTP messages can be typed using the MIME (Multipurpose Internet Mail Extension) type system. MIME has types such as text/html, application/octet-stream, and audio/mpeg3. HTTP also provides response status codes to inform the requester about whether a request succeeded and, if not, why. Table 1-1 lists some common status codes.

Table 1-1. Sample HTTP status codes and their meanings

Status code	In English	Meaning
200	OK	Request OK
303	See Other	Redirect
400	Bad Request	Request malformed
401	Unauthorized	Authentication error ...