Reviews : Java Books : Professional Java SOAP :

Buy this book Title: Professional Java SOAP ISBN: 1861006101 Price: $49.99 £36.99 C$74.95 © Wrox Press, Ltd.

SOAP

In the first chapter, we discussed several distributed object protocols and compared them to SOAP. Although it is not possible to cover all protocols, we now have a good idea of where SOAP stands: it is a simple XML-based protocol that supports RPC and messaging, primarily over HTTP. In this chapter, we will look at SOAP in more detail.

To broaden our understanding of SOAP and how the Apache framework implements this protocol, we will follow the organization of the SOAP specification. However, this chapter is meant to be an introduction to SOAP, not a reference. For an authoritative guide, you should always refer back to the SOAP 1.1 specification.

The SOAP 1. 1 specification can be found at http://www.w3c.org/TR/SOAP/, and the salient points are contained in Appendix A.

While we are looking through the SOAP specification, we will point out features that are either partially supported or not implemented in the Apache SOAP framework. The comprehensive list of what is and is not supported can be found at http://xml.apache.org/soap/features.html. The list of known interoperability issues with the Apache SOAP framework can be found at http://xml.apache.org/soap/docs/guide/interop.html.

Before getting into the specifics of SOAP, we will first have a look at the technologies that constitute its foundation.

We will then describe the anatomy of a SOAP packet:

• The SOAP envelope
• The SOAP header
• The SOAP body
• The SOAP fault

We will primarily focus on HTTP as the transport for SOAP packets.

We will then talk more specifically about the SOAP header and the SOAP envelope – this carries a request, a response, or a fault – and then we will discuss each of these in detail. In the course of this discussion, we will introduce the important topic of encoding and XML metadata.

Core Technologies

One of the design goals of SOAP is to be an open technology, from both a platform and a programming language point of view. The SOAP architects decided to meet this requirement by leveraging as many existing technologies as possible rather than inventing new ones.

For you, the SOAP developer, this means that you must be familiar with a variety of web technologies before being able to understand the SOAP specification. In no particular order, those technologies are:

• HTTP
• XML
• XML Namespaces
• XML Schemas

In addition, you must also be familiar with the prerequisites that we mentioned in the introduction to this book: basic object-oriented concepts and Java. We will introduce these core web technologies in the following sections. If you are already familiar with some or all of them, feel free to skip those sections and go directly to the SOAP section.

We will first talk about the protocol closest to the bits that travel over the wire: HTTP.

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