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https://issues.apache.org/jira/browse/FLINK-5221?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15725405#comment-15725405
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Till Rohrmann commented on FLINK-5221:
--------------------------------------
Hi [~shijinkui], the Flink distribution also contains the Scala classes and the
user function is loaded with the user code class loader. Thus, you should not
have the problem that you encounter a class not found exception. Otherwise this
points towards a bug in the system.
I think in general the decision to implement the Scala API on top of the Java
API as a thin layer is not a bad idea. This reduces complexity and helps to
avoid code duplication. Furthermore, I think that doing it vice versa would not
be optimal. The reason is that Scala contains concepts, such as traits, which
you cannot use from Java. So for example, if you define a trait in Scala
(containing a method definition), then you cannot simply extend the trait and
inherit this method.
Therefore, as far as I know, there are no plans to change this design
fundamentally in the near future.
> Checkpointed workless in Window Operator
> ----------------------------------------
>
> Key: FLINK-5221
> URL: https://issues.apache.org/jira/browse/FLINK-5221
> Project: Flink
> Issue Type: Bug
> Components: DataStream API
> Affects Versions: 1.2.0, 1.1.3
> Environment: SUSE
> Reporter: Syinchwun Leo
> Labels: windows
> Fix For: 1.2.0
>
> Original Estimate: 12h
> Remaining Estimate: 12h
>
> When window OPERATOR making checkpoint like this:
> class WindowStatistic extends WindowFunction[Event, Int, Tuple, TimeWindow]
> with Checkpointed[Option[List[Event]]] {
> override def appley()....
> override def snapshotState()...
> override def restoreState()
> }
> Window Operator couldn't invoke user defined function "snapshotState()". In
> debug model, line 123 in AbstractUdfStreamOperator.java returns false and
> can't make user defined state when checking the window whether is a
> Checkpointed instance. I think there is something wrong in userFunction var,
> it's a ScalaWindowFunctionWrapper object and it couldn't reflect if the user
> defined window extend Checkpointed Interface. Actually, the user defined
> window is kept in "func" var of userFunction.
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