All throwables (and not just exceptions) should be ignored in the shutdown hook. Failing to close these resources during shutdown is not a major problem, as they will be garbage collected by the backend anyways. Without this wide catch, some
applications will log a ClassNotFoundException when shutting down, which can be confusing for end users.

Fixes #949

Also fixes cloudspannerecosystem/liquibase-spanner#66 (comment)

Codecov Report

Merging #950 (06e24a8) into master (4088981) will increase coverage by 0.00%.
The diff coverage is 0.00%.

@@            Coverage Diff            @@
##             master     #950   +/-   ##
=========================================
  Coverage     85.22%   85.22%           
- Complexity     2651     2652    +1     
=========================================
  Files           145      145           
  Lines         14358    14358           
  Branches       1391     1391           
=========================================
+ Hits          12236    12237    +1     
+ Misses         1540     1539    -1     
  Partials        582      582           

Impacted Files	Coverage Δ	Complexity Δ
...m/google/cloud/spanner/connection/SpannerPool.java	87.36% <0.00%> (ø)	33.00 <0.00> (ø)
...cloud/spanner/connection/ReadWriteTransaction.java	82.11% <0.00%> (-0.28%)	59.00% <0.00%> (-1.00%)
...ud/spanner/SessionPoolAsyncTransactionManager.java	87.21% <0.00%> (+1.50%)	14.00% <0.00%> (+2.00%)

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Why is the class loader different during initialization vs finalization?

Why is the class loader different during initialization vs finalization?

I'm not sure exactly what happens, but globally speaking it seems to be caused by the fact that the shutdown hook is invoked when Maven is being shutdown, and not when the plugin is shutdown. So my hunch is the following:

1. Maven starts and runs the Liquibase plugin.
2. The Liquibase plugin dynamically loads the JDBC drivers and other services that it can find and then does its work.
3. The Liquibase plugin shuts down, but that does not shutdown the JVM.
4. Maven shuts down, which also shuts down the JVM, and that invokes the shutdown hook of the JDBC driver. But Maven does not know that the JDBC driver had been dynamically loaded by Liquibase.

Note: This is not a finalizer of a class, but a JVM shutdown hook, so it is only invoked when the entire JVM is shut down.

Thanks for the explanation @olavloite