Java Web Services: Up and Running, 2nd Edition

Chapter 5. SOAP Handlers and Faults

SOAP messages have some similarity to the HTTP messages that commonly transport them. Each type of message, SOAP and HTTP, can have a header and a body, although the header in a SOAP message is optional. In HTTP 1.1, there must be a header with at least the one key/value pair, with Host as the key, but HTTP headers usually contain at least a half dozen or so header elements. A SOAP message must have a body, which can be, but typically is not, empty. Not every HTTP message has a body, of course, with GET and DELETE messages as two bodyless examples. In each kind of message, the header, if present, is meant to contain metadata; the body, if present, is meant to contain data.

SOAP has a messaging architecture that centers on the different uses envisioned for the SOAP header and the SOAP body. At the base level of this architecture is the SOAP message, a one-way transmission from a sender to a receiver. The fundamental message exchange pattern (MEP) is thus one-way. SOAP-based applications such as web services are free to establish conversational patterns that combine one-way messaging in richer ways, for example, in the familiar request/response pattern that involves two one-way messages in the opposite direction. Even request/response and solicit/response are brief conversational patterns but these, too, can be combined to construct even richer patterns. There is no limit to how complex a SOAP conversational pattern may become.

A SOAP message has ...