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XML messaging with JAXM Part 1 of 2; how to exchange SOAP messages.

Article Excerpt
MESSAGING WITH JAXM

How to exchange SOAP messages

I could begin this article by expounding on the many applications that has found itself in, but that would be pointless. It's well known XML has found more than a niche in a variety of applications, in tiers of applications, and in all types of applications.

Messaging is one area of application development in which XML is being used more and more. Traditionally, messaging has been done using technologies like the Java Message Service, in which applications exchange data by sending the data to a queue; the data is then taken off the queue and processed by the intended recipient.

Applications that exchange messages must be concerned with how the message will be transported to the recipient. Protocols such as HTTP, FTP, and SMTP are used to define a standard transport for packaging information at a higher level.

Applications must also be concerned with how the payload or body of the message is encoded. Even though XML has become a popular encoding for exchanging messages, the need to have a standard encoding still exists. If every entity exchanging messages had its own encoding, it would be a nightmare to try to make sense of every message you received -- especially when your application may be concerned only with the payload of the message being sent, not necessarily how it got there.

Standards Are Needed

With the many variables present in application development, standards are evolving that will help speed the development and adoption of XML for messaging. Standards already exist for the various protocols that may be in use during execution of the application, ensuring a common understanding between applications that need to communicate. These standards are also being applied toward a common API for using these different technologies together.

Sun Microsystems, along with a host of other contributors, has developed the Java API for XML Messaging, or JAXM. JAXM provides a mechanism for exchanging SOAP messages. Using SOAP for the envelope to package your messages ensures a standard way to package them. At the time of this writing, Sun had just released the 1.0 version of the specification. The examples in this article were written using an Early Access version of the API.

Part 1 of this series focuses on utilizing JAXM to send SOAP messages directly to a recipient. Other functionality will be mentioned briefly, but I'll save the discussion for Part 2.

SOAP Basics

If you're not familiar with SOAP, I'll give you a brief introduction. If you are, skip ahead to the section titled "JAXM Overview."

SOAP -- Simple Object Access Protocol -- is an XML-based protocol for exchanging messages and executing remote procedure calls. Developed before JAXM, it continues to be developed as an independent specification by the W3C (www.w3c.org). SOAP specifies a schema that defines a set of elements and attributes that allow you to construct a SOAP message. For RPCs SOAP uses the XML Schema recommendation for representing serialized types. A simple SOAP message might look like the following:

XML Journal

SOAP messages define an envelope, headers, and a body to construct the SOAP message. A complete discussion of SOAP...

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