[FLINK-7251] Merge the flink-java8 project into corresponding flink project

[FangYongs]

What is the purpose of the change

Merge the codes in flink-java8 project into corresponding flink project

Brief change log

• Merge examples into flink-examples project
• Merge runtime test into flink-runtime project
• Merge test case into flink-tests project
• Remove flink-java8 project

Verifying this change

(Please pick either of the following options)

This changes are examples and test cases without any test coverage

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Yarn/Mesos, ZooKeeper: no

Documentation

• Does this pull request introduce a new feature? no

[zentol]

This would be easier to review (and for git to keep track of) if the individual commits would actually move a file, and not just copy them.

[FangYongs]

@zentol Thank you for your suggestion, it sounds good to me and I have fixed them, thanks

[zentol]

There's a compilation failure in flink-tests:

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.1:testCompile (default-testCompile) on project flink-tests_2.11: Compilation failure: Compilation failure:
[ERROR] /home/travis/build/apache/flink/flink-tests/src/test/java/org/apache/flink/test/streaming/runtime/StateBackendITCase.java:[67]
[ERROR] .map(new RichMapFunction<Tuple2<String, Integer>, String>() {
[ERROR] ^^^
[ERROR] The method map(MapFunction<Tuple2<String,Object>,R>) in the type DataStream<Tuple2<String,Object>> is not applicable for the arguments (new RichMapFunction<Tuple2<String,Integer>,String>(){})
[ERROR] /home/travis/build/apache/flink/flink-tests/src/test/java/org/apache/flink/test/example/client/JobRetrievalITCase.java:[99]
[ERROR] final ActorSystem actorSystem = actorSystemSeq.last();
[ERROR] ^^^^
[ERROR] The method last() is ambiguous for the type Seq<ActorSystem>

[zentol]

The StateBackendITCase can be resolved by bumping the tycho compiler version to 1.0.0, but the scala one remains.

[zentol]

Could you check what happens when you remove the tycho-compiler completely?

[FangYongs]

The JobRetrievalITCase is ok when I remove the tycho-compiler completely, I think it may be a bug of the tycho-compiler :(

[FangYongs]

Maybe it's better to move *ITCase to Flink-java project and rename them to *Test, I find it will be alright, what do you think? @zentol

[zentol]

Are you talking about things like FlatMapITCase? I would suggest to integrate these into the existing ITCase in flink-tests.

[FangYongs]

1. For the StateBackendITCase, it can be resolved by bumping the tycho compiler version to 1.0.0, but when I try to use tycho compiler version 1.0.0 in flink-java, it will cause lambda exception for LambdaExtractionTest. I think it's better to stay in the same version of tycho compiler in different flink project, so I try to modify the code of StateBackendITCase to resolve the problem directly.

2. For the JobRetrievalITCase, I try every version of tycho compiler, the problem always exists. I think tycho compiler may be incompatible with Seq.last() method. I try to use another method in Seq to get the last element in JobRetrievalITCase, and it would be ok

@zentol What do you think? Thanks :)

[zentol]

We will have to revert every change that requires the tycho plugin to be moved into any other module. Using a different for these modules may have performance impacts and possibly subtle bugs.

Sorry that i didn't notice it earlier.

[FangYongs]

@zentol Thank you for your reply, and I agree with you that the risk will be a little high for this PR. I'd like to close this PR if there's no better solution, thanks