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https://issues.apache.org/jira/browse/SOLR-972?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12665702#action_12665702
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Noble Paul commented on SOLR-972:
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bq.The persistence that I am concerned about is about the EventListener and
less about Context
The context is the single interaction point for all components with the system.
So it is better to be there. DIH does not yet guarantee any state persistence
between two imports . If it is a part of the Context API and documented it
becomes a standard way of storing data for all components. EventListener
cannot be seen as a special component.
All components are created on a per import basis. If we must cache , then we
must think of it for or all the the components
> EventListener-s creation changed from a per request ( full / delta-imports)
> scenario to once through the lifetime of the DIH plugin.
> ------------------------------------------------------------------------------------------------------------------------------------
>
> Key: SOLR-972
> URL: https://issues.apache.org/jira/browse/SOLR-972
> Project: Solr
> Issue Type: Improvement
> Components: contrib - DataImportHandler
> Environment: Java 6, Tomcat 6
> Reporter: Kay Kay
> Fix For: 1.4
>
> Attachments: SOLR-972.patch
>
> Original Estimate: 2h
> Remaining Estimate: 2h
>
> The EventListener plugin for notification of start / end import events
> (SOLR-938) creates an instance of EventListener before every notification.
> This has 2 drawbacks.
> * No state is stored between successive invocations of events as it is a new
> object
> * When writing plugins for delta imports - it is very inefficient to do a
> class loader lookup by reflection / instantiate an instance and call a method
> on the same.
> Attached patch has one EventListener through the lifetime of the DIH plugin .
> Also EventListener is changed to an interface rather than an abstract class
> for better decoupling (especially painful when the start/end eventlistener
> has an independent hierarchy by itself ).
> By default, a no-op listener is registered to avoid boiler plate code to
> check if there is a start / end listener specified. Efficient JRE impls
> should be able to optimize the no-op for minimum overhead compared to
> checking the reference for null and branching out.
> Specifying an onImportStart / onImportEnd overrides the default handler
> though.
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