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https://issues.apache.org/jira/browse/HADOOP-8549?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13409229#comment-13409229
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madhukara phatak commented on HADOOP-8549:
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Hi Harsha,
Thanks for looking at patch. Please find my reply for the concerns raised by
you.
bq. 1. No javadocs or any other form of dev-docs seem to be present. How
would others know how to use this feature? Lets document it.
Will add the appropriate javadoc for it once we finalize on implementation
bq. 2. I'm -1 on relying on protected member variables directly, as thats ugly
to do. Do something similar to ArrayWritable instead, where an inheritor passes
the class via a constructor. Or at least provide getter/setter of some form.
I tried it to make as ArrayWritable but it breaks the existing MapWritable
code since implementation class information has to be written into stream.
Even i tried setters/getters but it will not work since in M/R code Writables
are created through default constructor. So protected member was only way i can
think of solving the problem.
bq. The idea is good, but how does it work in terms of portability? If it is
written by client who used X impl. of map, and then read by another client who
used Y or the default impl., is it guaranteed to work? If yes, lets document
that guarantee. And if not, does it throw a proper error message?
Since client has to use different class to get the new behavior (ex
LinkedHashMapWritable) and Writables are not polymorphic, portability should
not be an issue.
Regards,
Madhukara Phatak
> Allow other implementation's of java.util.Map in MapWritable
> ------------------------------------------------------------
>
> Key: HADOOP-8549
> URL: https://issues.apache.org/jira/browse/HADOOP-8549
> Project: Hadoop Common
> Issue Type: Improvement
> Components: io
> Affects Versions: 2.0.0-alpha
> Reporter: madhukara phatak
> Assignee: madhukara phatak
> Priority: Minor
> Attachments: HADOOP-8549.patch
>
>
> Current implementation of MapWritable uses HashMap as Map implementation. But
> in some of the use cases we need other implementations of Map like
> LinkedHashMap,SortedMap.This jira changes visibility of 'instance' in
> MapWritable from private to protected which allows us to inject custom Map
> implementation through sub classing MapWritable .
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