During a restart, the Restarter runs all registered shutdown hooks. This
breaks Log4J2 as it leaves it in a shutdown state that leaves logging
switched off such that no output it produced when the application starts
up again.
This commit introduces a new RestartListener abstraction.
RestartListeners are notified prior to the application being restarted.
A Log4J2-specific implementation is provided that prepares Log4J2 for
restart by removing any shutdown callbacks from its shutdown callback
registry. This prevents the restart from shutting down Log4J2, ensuring
that it still functions when the application restarts.
Closes gh-4279
Prior to this commit, the devtools used bean factory post processors to
configure the environment with custom, development-time properties. This
meant that the environment was configured as part of the application
context being refreshed. Crucially, this happened after any property
conditions were evaluated making it impossible for the devtools to
change the default auto-configuration behaviour for a bean or
configuration class that was conditional on a property.
This commit moves the configuration of the environment into an
ApplicationListener that listens for the
ApplicationEnvironmentPreparedEvent which is published as soon as the
Environment has been prepared and before the application context is
refreshed.
Closes gh-3726
