[jira] [Commented] (FLINK-3511) Flink library examples not runnable without adding dependencies

["Till Rohrmann (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-3511?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15168826#comment-15168826 ] 

Till Rohrmann commented on FLINK-3511:
--------------------------------------

I agree with [~greghogan] that the best solution would be to move the gelly examples into their own module {{flink-gelly-examples}} which has the respective dependencies set to compile. That way users can easily run the examples and we don't clutter the {{flink-gelly}} jar.

> Flink library examples not runnable without 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
>            Assignee: Till Rohrmann
>
> 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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