public ServerListener build() {
        return new CallbackServerListener(serverStartingCallbacks, serverStartedCallbacks,
                                          serverStoppingCallbacks, serverStoppedCallbacks);
    }
Returns a newly-created {@link ServerListener} based on the {@link Runnable}s added to this builder.
core/src/main/java/com/linecorp/armeria/server/ServerListenerBuilder.java