Spring: BeanFactory vs ApplicationContext

// BeanFactory: lazy - a bean is created on the first getBean()
// ApplicationContext: eager - singletons are created at startup

var ctx = new AnnotationConfigApplicationContext(AppConfig.class);
// every singleton already exists here
OrderService s = ctx.getBean(OrderService.class);

Eager creation is a feature: a misconfigured bean fails at startup
rather than on the first request in production.