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https://issues.apache.org/jira/browse/KAFKA-8550?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16866044#comment-16866044
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Chris Egerton commented on KAFKA-8550:
--------------------------------------
I've tested for this against the latest for branches 2.0 through trunk; the
issue is present in all of them. It's probably present in pre-2.0 branches as
well but I haven't actually confirmed that yet.
> Connector validation fails with aliased converters
> --------------------------------------------------
>
> Key: KAFKA-8550
> URL: https://issues.apache.org/jira/browse/KAFKA-8550
> Project: Kafka
> Issue Type: Bug
> Components: KafkaConnect
> Affects Versions: 2.0.2, 2.3.0, 2.1.2, 2.2.2
> Reporter: Chris Egerton
> Assignee: Chris Egerton
> Priority: Major
>
> During connector config validation,
> [ConfigDef.validateAll(...)|https://github.com/apache/kafka/blob/1ae92914e28919a97520e91bfd0e588d55eb1774/clients/src/main/java/org/apache/kafka/common/config/ConfigDef.java#L497-L513]
> is invoked using a [Connector
> ConfigDef|https://github.com/apache/kafka/blob/trunk/connect/runtime/src/main/java/org/apache/kafka/connect/runtime/ConnectorConfig.java].
> This ConfigDef contains definitions for the [key and value
> converters|https://github.com/apache/kafka/blob/1ae92914e28919a97520e91bfd0e588d55eb1774/connect/runtime/src/main/java/org/apache/kafka/connect/runtime/ConnectorConfig.java#L72-L78],
> which have the type
> [ConfigDef.Type.CLASS|https://github.com/apache/kafka/blob/1ae92914e28919a97520e91bfd0e588d55eb1774/connect/runtime/src/main/java/org/apache/kafka/connect/runtime/ConnectorConfig.java#L167-L168].
> When plugin aliases are used for these configs, an error is encountered and
> the connector configuration is rejected.
> This error occurs because
> [Class.forName(...)|https://docs.oracle.com/javase/8/docs/api/java/lang/Class.html#forName-java.lang.String-boolean-java.lang.ClassLoader-]
> is used to load the classes for these configs during validation. Even though
> the DelegatingClassLoader used by Connect successfully loads the requested
> class in its
> [loadClass(...)|https://github.com/apache/kafka/blob/1ae92914e28919a97520e91bfd0e588d55eb1774/connect/runtime/src/main/java/org/apache/kafka/connect/runtime/isolation/DelegatingClassLoader.java#L358-L376]
> method, some (if not all) implementations of the Java runtime will then
> perform a check in their native Class.forName method to verify that the name
> of the loaded class matches the requested class name. For example, see [this
> section of
> OpenJDK|https://github.com/openjdk/jdk/blob/515e7600df738ebf8c42d38e322def012385e1b9/src/hotspot/share/classfile/systemDictionary.cpp#L1508-L1528]
> that performs the aforementioned check.
> A few possible fixes that come to mind include altering the connector
> validation in the AbstractHerder class to not use the
> ConfigDef.validateAll(...) method, or altering the logic used by the
> ConfigDef in its validateAll method for configs of type ConfigDef.Type.CLASS
> to use
> [ClassLoader.loadClass(...)|https://docs.oracle.com/javase/8/docs/api/java/lang/ClassLoader.html#loadClass-java.lang.String-]
> either instead of or in addition to Class.forName(...).
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