[ZEPPELIN-5574] ConcurrentModificationException in JsonResponse.toString() when getNote with restAPI

[zjffdu]

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What is this PR for?

The root cause of this issue is that when Note is serialized to json, it is being modified by another thread. This PR use thread-safe class for Note/Paragraph.

What type of PR is it?

[Bug Fix ]

Todos

• [ ] - Task

What is the Jira issue?

• https://issues.apache.org/jira/browse/ZEPPELIN-5574

How should this be tested?

• Tested it for 2 days in customer's environment and no issue happen again. (Before this PR, this issue happens everyday)

Screenshots (if appropriate)

Questions:

• Does the licenses files need update? No
• Is there breaking changes for older versions? No
• Does this needs documentation? No

[Reamer]

@zjffdu I want to try to solve the concurrent problem in pull request #4252 with a ReentrantReadWriteLock. This solution should also catch this pull request.

Give me some time for the implementation.

[zjffdu]

@Reamer Sure, let me know whey you are ready

[Reamer]

I merged #4252 into master. Please rebase to the current master. I think this PR is still needed.