[FLINK-4977] Enum serialization does not work in all cases

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 1.1.3
• Fix Version/s: 1.1.4, 1.2.0

Environment

Java SE 1.8.0_91
Ubuntu 14.04.4 LTS (trusty)

• Assignee: Stephan Ewen
• Reporter: Sean Winard
• Created: 31/Oct/16 17:49
• Updated: 04/Nov/16 14:11
• Resolved: 04/Nov/16 13:59

Description

Enums produce serialization failures whether they are by themselves or part of a POJO in the stream. I've tried running in IntelliJ IDEA and also via flink run. Here is a small program to reproduce:

package org.apache.flink.testenum;

import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;

public class TestEnumStream {
    private enum MyEnum {
        NONE, SOMETHING, EVERYTHING
    }

    public static void main(String[] args) throws Exception {
        final StreamExecutionEnvironment environment = StreamExecutionEnvironment.getExecutionEnvironment();
        environment.setParallelism(1);

        environment.fromElements(MyEnum.NONE, MyEnum.SOMETHING, MyEnum.EVERYTHING)
                .addSink(x -> System.err.println(x));

        environment.execute("TestEnumStream");
    }
}

Exception in thread "main" java.lang.RuntimeException: Cannot access the constants of the enum org.apache.flink.testenum.TestEnumStream$MyEnum
	at org.apache.flink.api.common.typeutils.base.EnumSerializer.createValues(EnumSerializer.java:132)
	at org.apache.flink.api.common.typeutils.base.EnumSerializer.<init>(EnumSerializer.java:43)
	at org.apache.flink.api.java.typeutils.EnumTypeInfo.createSerializer(EnumTypeInfo.java:101)
	at org.apache.flink.streaming.api.environment.StreamExecutionEnvironment.fromCollection(StreamExecutionEnvironment.java:773)
	at org.apache.flink.streaming.api.environment.StreamExecutionEnvironment.fromElements(StreamExecutionEnvironment.java:674)

I took a look at that line in EnumSerializer.java and swapped out the reflection on the "values" method for the simpler `enumClass.getEnumConstants()`, and that seems to work after I install my custom flink-core jar. I believe this is because http://docs.oracle.com/javase/tutorial/reflect/special/enumMembers.html specifically states you cannot reflect on the "values" method since it is implicitly generated at compile time.