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Axis: The next generation of Apache SOAP

Apache takes its SOAP implementation to new heights

By Tarak Modi, JavaWorld.com, 01/25/02

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Over the past couple of years, the Simple Object Access Protocol (SOAP) has taken off at rocket speed. A solid understanding of SOAP concepts has become essential for any strong software professional, especially software architects. The reason is quite simple. SOAP provides the foundation for one of the most exciting developments in the software industry today: Web services. Web services are exciting because they take application integration and interoperability to a new level never possible before, even with Java and J2EE (Java 2 Platform, Enterprise Edition).

To summarize, SOAP offers the following:

  1. An XML-based wire protocol, which is thus Web/firewall friendly
  2. A universally accepted W3C (World Wide Web Consortium) standard backed by all major and minor market players, including Microsoft, Sun Microsystems, IBM, and HP


Before diving into this article, you might want to review my previous JavaWorld series, "Clean Up Your Wire Protocol with SOAP," where I explain the basics of SOAP and why it proves so critical to the future of distributed computing:



In those articles, I focused on how developers could use Apache SOAP to build SOAP-based projects. Since then, Apache has completely rebuilt its SOAP implementation, creating a new project called Axis. In this article, I provide a high-level overview of the improvements Axis targets. I also show how to create and deploy a simple Web service with Axis.

What is Axis?

All software developers understand the importance of software toolkits; they prove essential to ensuring high developer productivity in this era of rapid application development. Coding with SOAP is no different. Although you could handcraft all your XML-based SOAP messages, you would probably want to use a SOAP toolkit to speed your development. After all, you don't handcode all your RPC (remote procedure call) messages in bits and bytes; why should SOAP messages be any different?

One such toolkit is available for SOAP. Apache SOAP's first generation was based on SOAP4J, IBM's donated codebase. I covered this excellent implementation in Parts 2 through 4 of my earlier series. As good as it was, Apache SOAP is now better. Axis is not just a rewrite of Apache SOAP, but a complete re-architecture. For Axis, Apache plans two alpha releases with partial functionality, a beta release with complete functionality, and a final release, Axis 3.0, which will supersede Apache SOAP 2.2. Alpha 1 was released in August 2001 and alpha 2 was released in September 2001. Though alpha 3 was issued in December 2001, this article focuses on the alpha 2 release (which features the same functionality as alpha 3).

When complete, Axis will:

  1. Support SOAP 1.1, just as Apache SOAP 2.2 does. For example, Axis will completely support the SOAP concept of mustUnderstand headers. Axis's final release will have a few SOAP 1.2 features as well as partial support for pluggable XML protocols.
  2. Likely prove much faster and more resource efficient than Apache SOAP, since it uses SAX (Simple API for XML) instead of DOM (Document Object Model). SAX allows lazy parsing of XML documents, which in many cases is more efficient -- especially when the entire XML document does not need to be parsed or kept in memory for long time periods.
  3. Have a clean and simple abstraction for designing transports -- i.e., senders and listeners for SOAP over various protocols such as SMTP (Simple Mail Transfer Protocol), FTP, message-oriented middleware, and so on. Also, the engine's core will be completely transport independent.
  4. Automatically generate WSDL (Web Services Description Language) from deployed services. The Axis alpha 2 version also comes with the wsdl2java tool for building Java proxies and skeletons from WSDL documents. Thus, you not only get the WSDL for an Axis-deployed service, but you can also build stubs and skeletons from the WSDL for extremely easy client code development. Note that the WSDL that feeds into the wsdl2java tool can originate from any source as long as it adheres to the WSDL specification. I'll show you an example of using this feature later.
  5. Support EJB (Enterprise JavaBeans) deployment as services. This resembles a feature provided by some application servers, such as BEA WebLogic Server.
  6. Feature improved deployment support and the ability to drop Java files into a deployment directory and expose the classes as services. I'll show you an example of this later.
  7. Better interoperate with Microsoft's SOAP implementation and .Net services. Over the past year, Apache and Microsoft have undergone several iterations of their SOAP implementations; with each iteration, they become more interoperable with each other. For details, see the summary of the last Apache/Microsoft interoperability meeting.


Although I use the future tense in the bullet points above, the alpha 2 release already includes many of these features.

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