Thursday, February 25, 2010

Controlling setup order for Spring DM applications

A quick and easy way to control the order in which Spring DM applications come up is using cardinality property in service imports.

Assume we have two applications app1 and app2 running in a single OSGi container and using Spring DM. Suppose we want app2 wait till app1 is initialized by Spring DM, we could do the following.
i) Export a service with appropriate interfaces / filters from app1.
For example:-
<osgi:service id="dependencyOSGi" ref="applicationDependency" interface="com.test.ApplicationDependency">
<osgi:service-properties><<entry key="application" value="app1-"/></osgi:service-properties>

ii) Imported the above service in app2 with a cardinality 1..1. The cardinality marks the service dependency as mandatory and causes Spring DM to delay the setup of app2 till the dependency is met (i.e. app1 is up an running).

<osgi:reference id="dependencyApp1OSGi" interface="com.test.ApplicationDependency" filter="(application=app1-" cardinality="1..1"/>

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