How Axis2 Handles SOAP Messages

How Axis2 Handles SOAP Messages




On each end, you have an application designed to deal with the (sent or received) messages. In the middle, you have Axis2, or rather, you can have Axis2. The value of Web services is that the sender and receiver (each of which can be either the server or the client) don't even have to be on the same platform, much less running the same application. Assuming that Axis2 is running on both sides, the process looks like this

• The sender creates the SOAP message.
• Axis "handlers" perform any necessary actions on that message such as encryption of WS-Security related messages.
• The transport sender sends the message.
• On the receiving end, the transport listener detects the message.
• The transport listener passes the message on to any handlers on the receiving side.
• Once the message has been processed in the "pre-dispatch" phase, it is handed off to the dispatchers, which pass it on to the appropriate application.
  

In Axis2, these actions are broken down into "phases", with several pre-defined phases, such as the "pre-dispatch", "dispatch," and "message processing", being built into Axis2. Each phase is a collection of "handlers". Axis2 enables you to control what handlers go into which phases, and the order in which the handlers are executed within the phases. You can also add your own phases and handlers.

Handlers come from "modules" that can be plugged into a running Axis2 system. These modules, such as Rampart, which provides an implementation of WS-Security, and Sandesha, which provides an implementation of WS-ReliableMessaging, are the main extensibility mechanisms in Axis2.

What is Axis2?

The Apache Axis2 project is a Java-based implementation of both the client and server sides of the Web services equation. Designed to take advantage of the lessons learned from Apache Axis 1.0, Apache Axis2 provides a complete object model and a modular architecture that makes it easy to add functionality and support for new Web services-related specifications and recommendations.

Axis2 enables you to easily perform the following tasks

• Send SOAP messages
• Receive and process SOAP messages
• Create a Web service out of a plain Java class
• Create implementation classes for both the server and client using WSDL
• Easily retrieve the WSDL for a service
• Send and receive SOAP messages with attachments
• Create or utilize a REST-based Web service
• Create or utilize services that take advantage of the WS-Security, WS-Reliable Messaging, WS-Addressing, WS-Coordination, and WS-Atomic Transaction recommendations
• Use Axis2's modular structure to easily add support for new recommendations as they emerge

To understand Axis2 and what it does, you must have a good idea of the life cycle of a Web services message

The sending application creates the original SOAP message, an XML message that consists of headers and a body.

If the system requires the use of WS* recommendations such as WS-Addressing or WS-Security, the message may undergo additional processing before it leaves the sender. Once the message is ready, it is sent via a particular transport such as HTTP, JMS, and so on.

The message works its way over to the receiver, which takes in the message via the transport listener. (In other words, if the application doesn't have an HTTP listener running, it's not going to receive any HTTP messages.) Again, if the message is part of a system that requires the use of WS-Security or other recommendations, it may need additional processing for the purpose of checking credentials or decrypting sensitive information. Finally, a dispatcher determines the specific application (or other component, such as a Java method) for which the message was intended, and sends it to that component. That component is part of an overall application designed to work with the data being sent back and forth.