Declare a public constant for the WebServerStartStopLifecycle's phase

[SmokeIT]

The (servlet and reactive) WebServerStartStopLifecycle.getPhase() method is currently hardcoded as:

@Override
public int getPhase() {
    return WebServerGracefulShutdownLifecycle.SMART_LIFECYCLE_PHASE - 1024;
}

It would be nice if this phase was declared as a public constant. This would make it easier to start a custom SmartLifecycle before an application starts accepting HTTP requests.

Currently we declare our own constant for this, but there is no guarantee the WebServerStartStopLifecycle phase will never change.

It is also not possible to depend on the webServerStartStop bean in order to obtain its phase, since dependency relationships take precedence over phases. That is, if Bean A depends on the webServerStartStop bean, it will be started after the webServerStartStop bean, regardless of Bean A's phase.

[philwebb]

WebServerStartStopLifecycle is a package-private class so adding a constant there won't help. Perhaps we could add something to ServletWebServerApplicationContext?

[wilkinsona]

There's the reactive side of things as well so I don't think it should be added to ServletWebServerApplicationContext . Perhaps WebServerApplicationContext though? The constant for the graceful shutdown phase could move there too.