Most Java developers use Spring Boot every day. Very few know what happens under the hood. Here's what actually runs when you hit @RestController: 1. Request hits the DispatcherServlet Every HTTP request goes here first. It's the front controller for the whole app. 2. HandlerMapping finds your method Maps the URL + HTTP method to the exact @RequestMapping method in your controller. 3. HandlerAdapter calls the method Invokes the method, resolves @PathVariable, @RequestParam, @RequestBody automatically. 4. HttpMessageConverter deserializes JSON Jackson reads the request body and converts it to your Java object. Silently. Every time. 5. Your business logic runs Finally, your actual code executes. 6. HttpMessageConverter serializes back Jackson converts your return object to JSON and writes it to the response body. 7. Response goes back through the filter chain Security filters, CORS headers, logging all happen on the way out too. Most developers only see step 5. Understanding steps 1–4 and 6–7 is what separates a Spring Boot user from a Spring Boot engineer. #Java #SpringBoot #BackendDevelopment #JavaDeveloper #SpringFramework #SoftwareEngineering #WebDevelopment #TechTips #Programming #FullStackDeveloper #C2C
Great breakdown-but one key addition: the request actually goes through the Servlet Filter chain before hitting DispatcherServlet, and Spring Interceptors wrap around controller execution. Understanding this full flow is what helps debug real production issues-not just writing controllers, but knowing why something breaks.
Strong post - this is the part of Spring Boot most developers never take time to understand. Knowing how the request actually flows under the hood makes debugging, customization, and performance tuning far more effective. This kind of depth is what truly separates framework users from engineers who can build and scale real systems.