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https://issues.apache.org/jira/browse/NIFI-7447?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17123992#comment-17123992
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ASF subversion and git services commented on NIFI-7447:
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Commit e31c323aa70dfe8f1bc7a3f39c216f9154529654 in nifi's branch
refs/heads/master from Mark Payne
[ https://gitbox.apache.org/repos/asf?p=nifi.git;h=e31c323 ]
NIFI-7447: When returning an object from a Controller Service, if that object
is defined as an interface, proxy that interface. This way, any method call
into the object will also change the classloader to the appropriate classloader.
> Objects returned from Controller Services may be invoked with the wrong
> ClassLoader
> -----------------------------------------------------------------------------------
>
> Key: NIFI-7447
> URL: https://issues.apache.org/jira/browse/NIFI-7447
> Project: Apache NiFi
> Issue Type: Bug
> Components: Core Framework
> Reporter: Mark Payne
> Assignee: Mark Payne
> Priority: Major
> Time Spent: 20m
> Remaining Estimate: 0h
>
> When a Processor calls a Controller Service, the framework changes the
> Thread's Context ClassLoader from the Processor's ClassLoader to the
> Controller Service's ClassLoader. This works well. However, when the object
> that is returned from a Controller Service has a method invoked, the Context
> ClassLoader is that of the Processor.
> This means that if the object returned attempts to load a class when its
> method is invoked, it's attempting to load it from the wrong ClassLoader.
> This can result in NoClassDefFoundError/ClassNotFoundException, etc.
> An example from the mailing list:
> ---------
> Hello,
>
> I try to implement a groovy script where I'm using jsonOutput.
> With nifi 1.5 the script works, but If I'm try to use the same groovy script
> with nifi 1.11.4, I get
> "unable to load FastStringService"
>
> example code :
>
> class GroovyRecordSetWriter implements RecordSetWriter {
> ....
> @Override
> WriteResult write(Record r) throws IOException {
> ...
> def j = JsonOutput.toJson([name: 'John Doe', age: 42])
> out.write(j.getBytes())
>
> ...
> ---------
>
> The problem here is that Controller Service returns a GroovyRecordSetWriter.
> When the processor calls #write, the Context Class Loader is the Processor's
> Context Class Loader, which knows nothing about Groovy. The call then
> delegates to `JsonOutput.toJson`. When this happens, Groovy, under the hood,
> attempts to load the `FastStringService` class using the Context Class
> Loader, which of course fails since the Context Class Loader is the
> Processor's ClassLoader and not the ScriptedRecordSetWriter's ClassLoader.
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