[jira] Resolved: (SOLR-972) EventListener-s creation changed from a per request ( full / delta-imports) scenario to once through the lifetime of the DIH plugin.

["Shalin Shekhar Mangar (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/SOLR-972?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Shalin Shekhar Mangar resolved SOLR-972.
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    Resolution: Won't Fix

An alternative exists for maintaining state and EventListeners should not be treated in a special manner. Therefore I'm marking this as "Won't Fix".

> 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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