7.2 ESB Service Invocation | Enterprise Service Bus: Theory in Practice

Like its predecessor, the client-server SOA, an ESB has the concept of a registry or directory service in which information about service endpoints is stored. An inherent find/bind/invoke operation occurs as part of the ESB mechanics, but it is separated out from the business logic. In an asynchronous ESB environment, the find/bind/invoke set of operations may actually map to sending an XML message to a queue or a publish-and-subscribe topic destination, and processing the reply. In the discussion of service containers in Chapter 6, we saw that the implementation of a service simply deals with an entry/exit endpoint metaphor. The service code focuses only on the implementation logic of a service. XML messages are received by the service from an entry endpoint that is managed by the service container. Upon conclusion of its task, the service implementation simply places its output message in the exit endpoint to be carried to its next destination. The output of the service is the reply, which the ESB routes to the next step (using the reply-forward pattern), or back to the requestor (using the request/reply pattern). The output message may be the same message that was received; the service may augment or modify parts of the message, or create a whole new "response" message. The operation of identifying and locating the next service in the chain, the binding to it, and the invocation of it is a set of tasks carried out by the ESB itself. The means by which the find/bind/invoke operations are defined is not through written code, but through configuration and deployment tools.

Table of content

Enterprise Service Bus: Theory in Practice

ISBN: 0596006756
EAN: 2147483647

Year: 2006
Pages: 126

Authors: David Chappell

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