Spring Core Concepts and Building a Mini Framework Without Spring
This article explains Spring's core features such as IoC, DI and AOP, demonstrates creating a simple Hello World service with Spring Boot, then shows how to implement the same functionality using raw Servlets and finally builds a miniature Spring‑like framework with custom annotations, an IOC container and a dispatcher servlet.
Spring is a framework designed to simplify enterprise Java development by providing IoC (Inversion of Control), DI (Dependency Injection) and AOP (Aspect‑Oriented Programming) features.
Using Spring Boot, a simple Hello World REST endpoint can be created with a Maven project, a pom.xml that includes spring-boot-starter and spring-boot-starter-web , a @RestController class and a main @SpringBootApplication class.
When Spring is unavailable, the same functionality can be implemented directly with the Servlet API: a web.xml mapping, a HelloServlet extending HttpServlet , and a Maven war packaging.
To illustrate Spring’s core ideas, a miniature framework is built:
A set of custom annotations ( @WolfController , @WolfService , @WolfAutowired , @WolfGetMapping , @WolfRequestParam ) are defined.
A MyDispatcherServlet loads application.properties , scans the base package, creates an IOC container, performs dependency injection, and registers handler mappings.
The HandlerMapping class stores request URL, target bean, method and parameter information.
Example controller HelloController and service HelloService demonstrate the workflow; a request to http://localhost:8080/hello?name=... returns “Hello：…”.
The article shows both the convenience of Spring and how its fundamental mechanisms can be reproduced manually, providing a deeper understanding of backend development in Java.
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