[WIP][FLINK-27966][python] All the classes move to the connector specific files

[a49a]

What is the purpose of the change

If all the classes are placed connectors/_init_.py, conflicts may happen that two classes belonging to two different connectors having the same name.

Brief change log

• Remove all classes from all list of connectors/_init_.py
• Reimport class from connector specific packages in test case
• reimport class from connector specific packages in examples

Verifying this change

This change is a trivial rework / code cleanup 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): (yes)
• The serializers: (no)
• The runtime per-record code paths (performance sensitive): (no)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: (no)
• The S3 file system connector: (no)

Documentation

• Does this pull request introduce a new feature? (no)
• If yes, how is the feature documented? (not applicable)

[a49a]

@dianfu Should we also move the file connector classes? If so, I will also change its corresponding docs.

[dianfu]

@deadwind4 Yes, of course. BTW, we should also considering the backward compatibility. One way that may work is adding the following code in the connector/init.py:

def _install():
    from pyflink.datastream.connectors import jdbc
    setattr(pyflink.datastream.connectors, 'JdbcSink', jdbc.JdbcSink)
    ...

_install()
del _install

[flinkbot]

CI report:

• 48f7c31 Azure: FAILURE

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[dianfu]

Closed which has been addressed in 9dd2b19995beb766f0cd0986b079f2d210c1e836