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https://issues.apache.org/jira/browse/FLINK-12725?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16861795#comment-16861795
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arganzheng commented on FLINK-12725:
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[~aljoscha] Yes, I compile with the change to use the context class loader and
it works just fine.
> Need to copy flink-hadoop-compatibility jar explicitly to ${FLINK-HOME}/lib
> location
> ------------------------------------------------------------------------------------
>
> Key: FLINK-12725
> URL: https://issues.apache.org/jira/browse/FLINK-12725
> Project: Flink
> Issue Type: Bug
> Components: Connectors / Hadoop Compatibility
> Reporter: arganzheng
> Priority: Minor
>
> I am currently working on an Flink application that uses some of the Hadoop
> dependencies to write the data to HDFS. On local environment it is working
> fine, however when I deploy this Flink application on the cluster it throws
> an exception related to compatibility issue.
> The error message that I am getting is
>
> {code:java}
> java.lang.RuntimeException: Could not load the TypeInformation for the class
> 'org.apache.hadoop.io.Writable'. You may be missing the
> 'flink-hadoop-compatibility' dependency. at
> org.apache.flink.api.java.typeutils.TypeExtractor.createHadoopWritableTypeInfo(TypeExtractor.java:2025)
> at
> org.apache.flink.api.java.typeutils.TypeExtractor.privateGetForClass(TypeExtractor.java:1649)
> at
> org.apache.flink.api.java.typeutils.TypeExtractor.privateGetForClass(TypeExtractor.java:1591)
> at
> org.apache.flink.api.java.typeutils.TypeExtractor.createTypeInfoWithTypeHierarchy(TypeExtractor.java:778)
> ....
> {code}
> I try to included the maven dependency of {{flink-hadoop-compatibility}} jar
> in POM dependency. But it is not detecting it. The Flink version I am using
> is 1.8.0
> However, when I explicitly copy the compatibility JAR to the
> {{${FLINK-HOME}/lib}} location, I am not getting any exception and able to
> run the Flink application successfully.
> I try dive into the source code, and find the problem:
> {code:java}
> package org.apache.flink.api.java.typeutils;
> public class TypeExtractor {
> /** The name of the class representing Hadoop's writable */
> private static final String HADOOP_WRITABLE_CLASS =
> "org.apache.hadoop.io.Writable";
> private static final String HADOOP_WRITABLE_TYPEINFO_CLASS =
> "org.apache.flink.api.java.typeutils.WritableTypeInfo";
> // visible for testing
> public static <T> TypeInformation<T> createHadoopWritableTypeInfo(Class<T>
> clazz) {
> checkNotNull(clazz);
> Class<?> typeInfoClass;
> try {
> typeInfoClass = Class.forName(HADOOP_WRITABLE_TYPEINFO_CLASS, false,
> TypeExtractor.class.getClassLoader());
> }
> catch (ClassNotFoundException e) {
> throw new RuntimeException("Could not load the TypeInformation for the class
> '"
> + HADOOP_WRITABLE_CLASS + "'. You may be missing the
> 'flink-hadoop-compatibility' dependency.");
> }
> ...
> }
> }
> {code}
>
> This is because `org.apache.hadoop.io.Writable` is mean to be loaded by
> TypeExtractor.class.getClassLoader() which is `AppClassLoader`, and the
> submited flink jar is loaded by `ParentFirstClassLoader`, which is the child
> of `AppClassLoader`, so `AppClassLoader` can not load
> `org.apache.hadoop.io.Writable` from your flink jar.
> I'm not sure if it's a bug, change to classLoader to
> `Thread.currentThread().getContextClassLoader()` will make it work without
> copy the flink-hadoop-compatibility jar file to ${FLINK-HOME}/lib location.
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