NIFI-6185: ListDatabaseTables processor doesn't close ResultSets

[lfrancke]

All this does is add two try-with-resources blocks. All the whitespace changes are only due to the new indentation of the blocks.

I have not added/changed the unit tests because honestly I wasn't sure how to test for this.

[lfrancke]

I believe the failed Travis builds to be unrelated.

[ijokarumawak]

The Travis build failures look like timeouts, not related to this change. I have successfully ran contrib-check locally with this PR. Change looks good tome, +1. Merging to master.

Do you see the same 'too many open cursors' error with other SQL processors, for example ExecuteSQL querying Oracle? I'm wondering if we need to fix those as well. Currently AbstractExecuteSQL doesn't close ResultSet.
https://github.com/apache/nifi/blob/master/nifi-nar-bundles/nifi-standard-bundle/nifi-standard-processors/src/main/java/org/apache/nifi/processors/standard/AbstractExecuteSQL.java#L256

Thanks @lfrancke for fixing this!

[lfrancke]

Thank you for the quick turnaround @ijokarumawak

I didn't look at all processors but AbstractExecuteSQL does close ResultSets implicitly via hasResults = st.getMoreResults(Statement.CLOSE_CURRENT_RESULT);

https://github.com/apache/nifi/blob/master/nifi-nar-bundles/nifi-standard-bundle/nifi-standard-processors/src/main/java/org/apache/nifi/processors/standard/AbstractExecuteSQL.java#L352

[ijokarumawak]

That's right, thanks @lfrancke! I only looked at the code around ResultSet, not with the statement :)