Márton Balassi created FLINK-3511:
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Summary: 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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