tomcat-jdbc check if returned connection is closed

[panchenko]

https://bz.apache.org/bugzilla/show_bug.cgi?id=64083

I had a situation when driver closed connection because of I/O error, bur connection has been added to the avaialble ones and then returned to another caller.
The testOn* properties were not enabled in that case.

It looks like the pool can easily check if connection has been closed and don't accept it back.
WDYT?

[ChristopherSchultz]

I don't see how this test-case actually tests the change. There is no check to see if the connection in the pool is not damaged, or a complaint if it is damaged.

[panchenko]

The test checks that connection obtained from the pooll second time can be used for query execution.
Without this pool code change it returns the closed connection and query exection fails.

I agree the intent is not fully clear, as it tests it as black-box, I will check if some white-box asserts can be added.

[zyu-godaddy]

Also reported: https://bz.apache.org/bugzilla/show_bug.cgi?id=66502

This bug is the only bug that has been bugging us; otherwise the pool works flawlessly.

I wonder if you people want to revisit this issue; or I can offer to work on it.

[markt-asf]

If you can address Chris's concerns with the test then I don't see why this PR (or one based on it) could not be merged.

[zyu-godaddy]

Cool, I will.

[zyu-godaddy]

While this change makes sense to me, and it should be inexpensive for the jdbc driver I am using (mysql-connector-java), I don't feel comfortable to add this check unconditionally without knowing the full impact. So I am not going to pursue this approach.

Instead, I will try setDiscarded(true) in an interceptor conditional on failed query and isClosed.

[panchenko]

@markt-asf @ChristopherSchultz Addressed the comments about test, please take a look