Change config loading order to give URLs precedence

[ryannedolan]

Summary

Change config loading order in JDBC drivers to consistently give URL properties precedence over getConnection()'s properties.

Details

JDBC drivers may be loaded via the older DriverManager mechanism or via the newer DataSource mechanism. With the former, drivers may be loaded as getConnection(url, props), where props are optional connection properties. The URL itself very often includes connection properties, raising the question of which source of properties takes precdence.

The JDBC docs do not specify what should happen here, explicitly leaving it to the drivers to decide.

Given that end users can often only control and see the URL, we think it makes sense to given the URL precedence here. In that case, the props supplied to getConnection() should be considered defaults rather than overrides.

The opposite approach would yield surprising behavior, when e.g. a log showed jdbc:foo://bar=qux while the driver silently overwrote bar.

Testing

None. Integration tests should cover this trivial change.