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Patterns: Implementing Self-Service in an SOA Environment by Fernando Teixeira, Shashi Shrimali, Peter Hood, Sandy Grewal, Diego Cotignola, Anup Aggarwal, Carla Sadtler

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222 Patterns: Implementing Self-Service in an SOA Environment
Figure 7-37 Service integration buses in a multiple-bus topology
For details about the bus, please refer to WebSphere Application Server V6
System Management and Configuration Handbook, SG24-6451.
7.6.2 Mediations
A mediation in the WebSphere Application Server service integration bus
processes inflight messages between the production of a message by one
application, and the consumption of a message by another application.
Mediations provide you with functionality to customize the messaging behavior of
the bus. This may include processing such as:
򐂰 Transforming a message from one format into another.
򐂰 Routing messages to one or more target destinations that were not specified
by the sending application.
Chapter 7. Application and system design guidelines 223
򐂰 Augmenting messages by adding data from a data source.
򐂰 Distributing messages to multiple target destinations.
A mediation is associated with a destination on the bus to create a mediated
destination. A mediated destination has two parts:
pre-mediated and
post-mediated. Applications send messages to the pre-mediated part, and
receive them from the post-mediated part. A mediation receives messages from
the pre-mediated part, transforms the messages in some way, and places one or
more messages on the post-mediated part. In this way, the mediation controls
the progress of messages to their intended target destination.
A mediation can operate within a global unit of work to ensure transactional
integrity. Several mediations can operate at the same time to improve the
throughput of messages at a destination.
The behavior of a mediation is defined by a mediation handler list. Mediation
handler lists contain one or more mediation handlers.
Mediation handlers
A mediation handler is a Java program that performs the function of a mediation,
and can be deployed in a mediation handler list. The mediation handler class
implements the following interface:
com.ibm.websphere.sib.mediation.handler.MediationHandler.
A mediation handler can have properties that control its behavior.
A mediation handler is packaged for deployment with a supplied EJB. At
deployment, you can set properties to control the behavior of the mediation at
run-time, and specify membership of one or more mediation handler lists. You
deploy a mediation handler as an EAR file and install it into WebSphere
Application Server.
Mediation handler lists
A mediation handler list is a collection of mediation handlers that are invoked in
sequence.
A mediation handler list is a simple pipeline of mediation handlers. The same
parameters are passed from one mediation handler to the next mediation
handler in the list.

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