What is the Java version Apache Flink is supposed to work with?
8 and 11. Non-LTS Java11+ releases _should work_, but we don't put in effort to make it as convenient as for LTS releases. As such you have to manually enable the java11 profile when compiling Flink.
I set the target version to 11 since IIRC we ran into more errors that way, ensuring a smoother transition once Java 11 is the default.
On 30/06/2020 13:01, Niels Basjes wrote:
Hi, I have both JDK 8 and 14 on my system and yesterday I ran into this exception (I put the info I have in this ticket https://issues.apache.org/jira/browse/FLINK-18455 ) : java.lang.NoSuchMethodError: java.nio.ByteBuffer.position(I)Ljava/nio/ByteBuffer; >From digging around ( https://stackoverflow.com/questions/61267495/exception-in-thread-main-java-lang-nosuchmethoderror-java-nio-bytebuffer-flip ) it seems this is caused when using JDK 9+ without setting '-release 8' and then running with JDK 8. Essentially there are two solutions I see a lot: 1) Add the -release 8 flag to the compiler 2) Use the flaky workaround to cast all problem cases to the superclass implementing the method (i.e. cast to java.nio.Buffer) Looking at the actual Flink code I found that In a JDK 8 build both source and target are set to Java 8 https://github.com/apache/flink/blob/d735d8cd8e5d9fae5322001099097581822453ae/pom.xml#L109 <java.version>1.8</java.version> https://github.com/apache/flink/blob/d735d8cd8e5d9fae5322001099097581822453ae/pom.xml#L115 <maven.compiler.source>${java.version}</maven.compiler.source> <maven.compiler.target>${java.version}</maven.compiler.target> In a JDK 11 build a profile is activated that overrides it to Java 11 https://github.com/apache/flink/blob/d735d8cd8e5d9fae5322001099097581822453ae/pom.xml#L938 <profile> <id>java11</id> <activation> <jdk>11</jdk> https://github.com/apache/flink/blob/d735d8cd8e5d9fae5322001099097581822453ae/pom.xml#L1004 <artifactId>maven-compiler-plugin</artifactId> <configuration> <source>11</source> <target>11</target> So when building with Java 11 the output classes are Java 11 compatible binaries. However I have Java 14 (and the 'java11' profile is only activated at the EXACT version of java 11) so it stays at source and target 1.8 but does not specify the "release 8" setting. ... which causes the problems I see. Looking at the current build settings I was puzzled a bit and I have this main question: What is the Java version Apache Flink is supposed to work with? Currently I would expect Java 8. So what I propose for this problem as a fix is to set source, target and release to Java 8 for all compiler versions (i.e. also Java 9, 11, 14, ...). That way you can use any compiler and get the correct results. I also am curious if that would fix the tests that seem to fail under Java 11. What do you think is the correct approach for this?
