Chapter 15. Web Services
Depending on who you talk to, web
services are as simple as a set of remote interfaces for an
application or as complex as a complete reinvention of the Internet.
As is generally the case, the truth lies somewhere in between. As you
write enterprise applications, you will find that you often want to
expose them to non-Java clients. This chapter details how to take on
this task, at least within the context of web services. It examines
both simple and complex applications of web services, and gives you a
good idea of how to get started in this area of programming.
On the simple end of the spectrum, you can create a web service by
providing an application programming
interface (API) that is exposed as a set of remote procedure calls
(RPC) over the Internet. An example of this is a wholesale business
that wishes to provide a set of programmatic interfaces for merchants
to verify (in real time) the current inventory of a product, and then
order products that are in stock.
At the other end of the spectrum, web services can describe a
complete framework for reworking the Internet itself, where HTML and
hyperlinks are replaced by a complex system of registries, portable
objects, XML-based interfaces to sites with dynamic discovery, or
complex and hyper-intelligent models for business-to-business
transactions. Obviously this view is a bit extreme, and best avoided
for the sake of time, space, and general sanity.
This chapter looks at web services as an RPC mechanism. In
particular, it focuses on one of RPC's simplest
mechanisms, XML-RPC, and describes the differences between XML-RPC
and its more sophisticated cousin, SOAP.
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