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https://issues.apache.org/jira/browse/FLINK-3511?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15167416#comment-15167416
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Márton Balassi commented on FLINK-3511:
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I am against moving the examples of a library out of the library. It would also
mean that flink-examples-batch would need to depend on gelly, which would add
gelly automatically as a dependency to flink-dist, something that we would like
to avoid as long as it is beta.
And even if we did, it would only heal one single symptom instead of curing the
underlying problem. With the current solution any example in any library is a
potential victim of this issue.
> Flink library examples not runnable withput adding dependencies
> ---------------------------------------------------------------
>
> Key: FLINK-3511
> URL: https://issues.apache.org/jira/browse/FLINK-3511
> Project: Flink
> Issue Type: Bug
> Components: Build System
> Affects Versions: 1.0.0
> Reporter: Márton Balassi
>
> Recent changes to the build [1] where many libraries got their core
> dependencies (the ones included in the flink-dist fat jar) moved to the
> provided scope.
> The reasoning was that when submitting to the Flink cluster the application
> already has these dependencies, while when a user writes a program against
> these libraries she will include the core dependencies explicitly anyway.
> There is one other case of usage however, namely when someone is trying to
> run an application defined in these libraries depending on the core jars. To
> give an example if you were to run the Gelly ConnectedComponents example [2]
> from an IDE after importing Flink (or running with java -jar without
> including the flink fat jar in the classpath) you would receive the following
> class not found exception as per the current master:
> Exception in thread "main" java.lang.NoClassDefFoundError:
> org/apache/flink/api/common/ProgramDescription
> at java.lang.ClassLoader.defineClass1(Native Method)
> at java.lang.ClassLoader.defineClass(ClassLoader.java:760)
> at
> java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
> at java.net.URLClassLoader.defineClass(URLClassLoader.java:467)
> at java.net.URLClassLoader.access$100(URLClassLoader.java:73)
> at java.net.URLClassLoader$1.run(URLClassLoader.java:368)
> at java.net.URLClassLoader$1.run(URLClassLoader.java:362)
> at java.security.AccessController.doPrivileged(Native Method)
> at java.net.URLClassLoader.findClass(URLClassLoader.java:361)
> at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
> at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
> at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
> at java.lang.Class.forName0(Native Method)
> at java.lang.Class.forName(Class.java:264)
> at com.intellij.rt.execution.application.AppMain.main(AppMain.java:122)
> Where the class missing in runtime is in flink-core, a transitive dependency
> of the jars moved to the provided scope.
> Funny thing is we have tests in place to run our examples, but those add test
> scope dependencies re-adding the missing classes, so it is never discovered.
> I agree with the original purpose of PR #1683, but also think that the
> current state makes for very inconvenient user experience.
> I would like to open a discussion on how and when to resolve the issue given
> the release of 1.0.0.
> 1. Is it a release blocker?
> 2. Should the change be reverted or is it sufficient to have proper
> documentation around it? Maybe a maven profile for explicitly for developing
> Flink without the provided scope?
> Note that the issue was originally reported by Gábor Gévay.
> [1] https://github.com/apache/flink/pull/1683
> [2]
> https://github.com/apache/flink/blob/master/flink-libraries/flink-gelly/src/main/java/org/apache/flink/graph/example/ConnectedComponents.java
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