Java and SOAP

Chapter 2. The SOAP Message

All SOAP messages are packaged in an XML document called an envelope, which is a structured container that holds one SOAP message. The metaphor is appropriate because you stuff everything you need to perform an operation into an envelope and send it to a recipient, who opens the envelope and reconstructs the original contents so that it can perform the operation you requested. The contents of the SOAP envelope conform to the SOAP specification,^[1] allowing the sender and the recipient to exchange messages in a language-neutral way: for example, the sender can be written in Python and the recipient can be written in Java or C#. Neither side cares how the other side is implemented because they agree on how to interpret the envelope. In this chapter we’ll get inside the SOAP envelope.

The HTTP Binding

The SOAP specification requires a SOAP implementation to support the transporting of SOAP XML payloads using HTTP, so it’s no coincidence that the existing SOAP implementations all support HTTP. Of course, implementations are free to support any other transports as well, even though the spec doesn’t describe them. There’s nothing whatsoever about the SOAP payload that prohibits transporting messages over transports like SMTP, FTP, JMS, or even proprietary schemes; in fact, alternative transports are frequently discussed, and a few have been implemented. Nevertheless, since HTTP is the most prevalent SOAP transport to date, that’s where we’ll concentrate. ...