Spring beans are most commonly created through constructors or @Bean factory methods, but there is a third, lesser-known option: static factory methods. When a class uses the factory pattern to control its own instantiation — for example, a connection pool, a registry, or a singleton that validates its configuration at construction time — a static factory method lets Spring call that factory instead of a constructor. This keeps your code idiomatic and avoids adding unnecessary public constructors just to satisfy the IoC container.

Spring MVC is the foundational web layer of the Spring Framework, and it remains a favourite topic in Java developer interviews at every level. Even in a world dominated by Spring Boot auto-configuration, interviewers probe Spring MVC knowledge to gauge whether a candidate truly understands what happens under the hood. This guide covers the 40 most-asked Spring MVC interview questions, organised from core concepts through advanced topics, each with a concise, interview-ready answer.

An ETag (Entity Tag) is a short fingerprint — typically an MD5 or SHA hash of a resource’s content — that a REST API includes in every response. On the next request, the client sends the ETag back in a If-None-Match header. If the resource has not changed, the server replies with 304 Not Modified and an empty body, saving bandwidth and time. In this guide you will learn how ETags work, implement them from scratch in a Spring Boot REST API, and apply conditional updates to prevent lost updates in concurrent systems.