Upgrade HikariCP to 1.4.0

[snicoll]

see comment in #1160

[brettwooldridge]

NP. If you need a pull request, let me know.

[wilkinsona]

I purposefully chose 1.3.9 rather than 1.4.0 as, given that the change was being made in a maintenance release of Boot, I only wanted to pick up a new maintenance release of the dependency.

@brettwooldridge How are you versioning Hikari? Is the 1.3.x line now dead? Is 1.4.0 a drop-in replacement for users who were on 1.3.x?

[brettwooldridge]

In HikariCP, versioning works by incrementing the least significant digit, and upon reaching '9', incrementing the next significant digit. The first version was 1.0.0, so there were 40 releases leading up to 1.4.0. The 1.3.3 release was the only one that introduced "breaking" changes by the removal of certain pool properties. Except for that, every release is designed to be a drop-in replacement for the previous.

The next release of HikariCP however will restart the version number at 2.0.0. This is because the published artifacts have been split into a Java 6/7 version and a Java 8 version. In the next release, the artifact that users have known as "HikariCP" will be the Java 8 version, and users needing Java 6/7 compatibility will use the "HikariCP-java6" artifact. Spring-boot probably falls into this later category.

When HikariCP 2.0 is released, I will submit a pull request to you guys with the required dependency change.

[philwebb]

@brettwooldridge Have you considered using semantic versioning or something similar for Hikari? Incrementing the minor version when it reaches '9' is a little unusual. I would have expected the version to be 1.3.10 if it was just a bug-fix release.

[philwebb]

@wilkinsona I've targeted this for 1.1.5 given that HikariCP 1.4.0 is just an incremental upgrade from 1.3.9. Should if you'd rather defer this until 1.2.

[brettwooldridge]

@philwebb I like it. From the 2.0.0 release I will start with semantic versioning.