Axis 2 is a web
service/SOAP/WSDL engine provided by Apache. It is a java based
implementation.
Think about a bank
doing day to day transactions on their hundreds of branches and each
one of them are connected with each other. In this scenario, you can
understand that the computing resources are “Distributed” among
several locations (Branches). To achieve this kind of computing need,
we use a Distributed Computing System in which the
computers and resources are distributed in several physical and
logical locations.
These systems need
to be developed as separate systems but they need to be
interconnected when needed and all of these systems should be
accessible from the web interface which is present at the computers
of bank officers. We can develop these systems as Services and then
we can inter-connect these services in to a common architecture
(platform). This kind of system is called as a Service Oriented
Architecture (SOA).
Representation of
what is happening inside an axis2 engine :
Handlers
Handler is the message interceptor. Which intercepts the messaging
flow and does whatever task it is assigned to do. In fact, the
interceptor is the smallest execution unit in a messaging system.
Handlers, in Axis,
are stateless, meaning they do not keep their past execution states
in memory.
Handler can read
SOAP messages, remove elements from the message (mostly headers), add
new elements (headers), or modify elements as well as add, delete,
or
modify content from the Message Context.
Phases
The concept of a phase is introduced by Axis2 and it was mainly to
support the dynamic ordering of handlers to provide better
extensible, and better flexibility of the handler chain. A phase
can be defined in various ways:
• It can be considered
as a logical collection of handlers
• It can be
considered as a specific time interval in the message execution
•
It can be considered as a bucket into which one can put his/her
handler
• One can consider a phase as a handler too
Pipe (Flow)
A flow is the message pipe where the message enters from one end
of the flow and leaves from the other end of the flow. A flow or
execution chain can be considered as a collection of phases.
At a very high
level, what the engine really does is call the invoke method of each
phase in a given flow, and then the phase will sequentially invoke
all the handlers in it.
