Chapter 17: Web Services

Overview

Web Services is a complex subject in and of itself. Entire books have been written on every facet of it, including books on Web Services architecture, security, managing Web Services, performance tuning, and more. As part of the Oracle documentation set for Oracle Application Server 10 g , the Oracle Application Server Web Services Developers Guide for 10 g , as one example, is 382 pages long. A search on a popular online book site returned no less than 64,396 matches when queried for Web Services. Programmers should have little trouble finding information on the architecture, implementation, and deployment of every aspect of Web Services. The real question at hand is how many pages does it really take to understand the technology? Thousands? Less than 50?

This chapter will provide all the typical Oracle developer will need to know to get excited about this technology, as well as properly demonstrate why everything you do going forward should have some Web Services component ”because it should. All indications point to service-oriented architectures (i.e., an architecture with Web Services at the center) as the wave of the future. This chapter summarizes thousands of pages of information into the absolute essentials to begin developing Web Services applications. As Mark Twain once said, If I had more time, I would have written a shorter letter. This is the shorter letter. You can read countless pages about SOAP and XML ... or you can take a few hours and read this part of the book.

This chapter represents one of the most important and least understood technologies: Web Services. The serious players in the software industry (Oracle, IBM, and Microsoft) have decided to abandon their proprietary technology roots and adopt open standards for sharing information. Sharing information across systems is a good thing for the IT industry.

It s important to know that Oracle Application Server 10 g and the stand-alone Oracle Application Server Containers for J2EE (OC4J), which is available as a separate download from Oracle Technology Network (http://otn.oracle.com), both fully support Web Services. It s also important to understand that if you choose to use Oracle JDeveloper 10 g , you ll be able to cut down your Web Services learning curve considerably. Oracle JDeveloper 10 g allows the developer to easily create Web Services from existing Java classes or PL/SQL-packaged program units in a very short period of time. The wizards help you create, package, and deploy your Web Services. Oracle JDeveloper 10 g automatically generates stubs and other files, such as Web Services Description Language (WSDLs). Oracle Application Server 10 g also creates a home page automatically for each deployed Web Service. Simply put, if you are serious about Web Services and have the resources, make the effort to learn and use Oracle JDeveloper 10 g . The examples in this chapter are built using it. Doing this work manually (i.e., not exploiting the various tools and wizards available in Oracle JDeveloper 10 g ) requires considerably more reading and more development work, and has a much higher potential for error.

Oracle has identified Web Services as a key technology. The Oracle Technology Network (OTN) at http://otn.oracle.com/tech/ webservices /index.html offers a vast amount of good information. In particular, the site provides extensive information on such things as JDeveloper extensions, online documentation, step-by-step tutorials, code samples, discussion forums, technical documents, and much more.

What are Web Services? Stated in its simplest form, a service is a program. Web Services allow programs to be:

• Published

• Located

• Invoked from the network (i.e., the Web)

In other words, Web Services simply allow a program on another server to be run as if that program is running on your server. You could think of a Web Service as a remote subroutine which can be written in any language and could be running anyplace in the world. As you ll see in this chapter, this provides the ultimate scalability, reliability, and openness developers previously only dreamt about. Service-oriented architecture was mentioned above. It s made up of services (i.e., programs) that communicate via Web Services. Web Services are commonly described as:

• Self-contained objects Black boxes that live on their own. You ll see that this is true and they do stand on their own.

• Self-describing Meaning they can tell you all about their required inputs and expected outputs for each available method (i.e., program unit) within them. We ll talk about the WSDL (pronounced wiz-dil) in a minute.

• Modular We remember from our best practices that modular programming is good. A Web Service can be as granular as you want it to be.

• Loosely coupled If the Web Service is changed (i.e., new inputs and outputs are added), it won t break the programs calling it.

• Platform and application independent This one speaks for itself, but the fact that you can call a Web Service and it doesn t matter what platform it s running on, or what application it s part of, is very powerful.

You ve probably heard that entire trade shows have been built around Web Services. Many vendors are making BIG bets on them (i.e., former Forte developers). While Web Services have revolutionary potential to transform technology, adoption of all new technologies is evolutionary (and MUCH slower than people had hoped). The adoption of Web Services should increase dramatically in the near future as Web Services have the additional benefit of making use of existing infrastructures . In other words, a Web Service can call existing programs that are in place today.

Can you think of something that has provided huge improvement in the business communications world? How about the fax machine? With fax machines, you can close a contract in 1/10th the time you could previously. It has been so successful that more than 150 billion faxes are now sent each year. What does that have to do with Web Services? One of the first business applications of Web Services is to enable better business communication, hence better business integration. Web Services are cheap business links that drive strategy. If you re interested in learning more on where to begin implementing Web Services into your organization, we recommend reading papers from Ted Schadler of Forrester Research (http://www.forrester.com/find).