How Spring Container and Component Scanning Work Together

Understanding HandlerInterceptor Order in Spring Boot When you register multiple HandlerInterceptors in a Spring Boot application, have you ever wondered which one runs first? Here’s how Spring decides the order: Unlike Filters (which use @Order), HandlerInterceptors run in the order they are registered inside your WebMvcConfigurer. #SpringBoot #Java #SoftwareEngineering #BackendDevelopment #SpringMVC #CleanArchitecture

⚙️ Bean Lifecycle in Spring Every Spring bean goes through stages like instantiation, dependency injection, initialization, and destruction. Developers can customize these steps using lifecycle annotations such as @PostConstruct and @PreDestroy. Spring automatically manages this entire lifecycle, ensuring optimal resource handling and clean object management. 🔁 #SpringBoot #SpringFramework #Java #SpringBeans #Lifecycle #BackendDevelopment

@Component vs @Bean @Component marks a class for automatic bean detection via scanning. @Bean defines a bean manually inside a @Configuration class. Use @Component for simple POJOs and services. Use @Bean when you need full control over object creation. Both ultimately register beans in the Spring container. #SpringFramework #Java #SoftwareEngineering #BackendDevelopment

Bean Scopes & Object Management Spring supports multiple scopes like singleton, prototype, request, and session. Singleton creates one shared instance for the entire application. Prototype creates a new instance every time it’s requested. Choosing the right scope improves memory and performance. It helps control how objects live inside your application. #SpringFramework #Java #SoftwareEngineering #BackendDevelopment

🔹 Spring Scopes in a Nutshell Session bean → Singleton dependency ✅ Each user gets their own session bean All share the same singleton Singleton → Session dependency ❌ Singleton can’t directly hold a session bean Spring injects a proxy (like a mailbox) When the singleton calls a method, the proxy delivers it to the correct session bean for the current user 💡 Analogy: Session → Singleton: each user has their notebook, everyone uses the same pen ✍️ Singleton → Session: singleton talks to a mailbox, which routes messages to the right notebook 📬 Mix scopes carefully — proxies make it safe! #SpringBoot #Java #SessionScope #Singleton #BackendEngineering #SpringTips

𝗜𝗳 𝘆𝗼𝘂 𝘂𝘀𝗲 𝗝𝗥𝗘... 𝘄𝗵𝘆 𝗱𝗼 𝘆𝗼𝘂 𝘀𝘁𝗶𝗹𝗹 𝗻𝗲𝗲𝗱 𝗝𝗩𝗠? Most devs get this backward. Let’s fix it once and for all. You don’t 𝘳𝘶𝘯 Java with JRE. You 𝘳𝘶𝘯 Java 𝗶𝗻𝘀𝗶𝗱𝗲 the JVM. The 𝗝𝗥𝗘 is just the environment — it gives the 𝗝𝗩𝗠 what it needs to do its job: standard libraries, config files, runtime support. Think of it like this 👇  • 𝗝𝗩𝗠 → the engine  • 𝗝𝗥𝗘 → the car that holds the engine  • 𝗝𝗗𝗞 → the factory that builds the car You don’t drive an engine. You drive a car. The car uses the engine to move. Same with Java. The 𝗝𝗥𝗘 𝘂𝘀𝗲𝘀 𝘁𝗵𝗲 𝗝𝗩𝗠 to run your code. Once you get this mental model, Everything about Java’s ecosystem suddenly clicks. #java #jre #jvm

🧩 Spring Boot Tip: Simplify Dependency Injection with @Autowired Constructor! Want cleaner beans and easier testing? Use constructor injection with Spring’s @Autowired on constructors—making your dependencies explicit and your classes immutable. ✨ Example: @Service public class UserService { private final UserRepository userRepository; @Autowired public UserService(UserRepository userRepository) { this.userRepository = userRepository; } } Benefits: Easier unit testing, mandatory dependency injection, and clearer design. 💡 Pro Tip: Starting from Spring 4.3, @Autowired on constructors is optional if the class has a single constructor. How do you prefer to inject dependencies in your Spring apps? Share your favorite DI style! #SpringBoot #Java #DependencyInjection #Autowired #CleanCode #BackendTips #DesignPatterns

Today I learned something interesting about Spring Boot’s @Async annotation. I was debugging why an async method wasn’t actually running in parallel — and eventually realized it was because I was calling it from within the same class. Since the call never went through the Spring proxy, the @Async behavior didn’t trigger. Lesson: @Async only works when the method is invoked through a Spring-managed proxy — not via direct internal calls within the same bean. Moving the method to a separate service (or injecting the bean itself via a proxy) fixed it instantly. A small reminder that many “magic” framework features are really just smart proxies under the hood — and understanding how they work can save hours of debugging. Have you ever run into similar proxy or async surprises in Spring Boot? #TodayILearned #SpringBoot #Java #Microservices #BackendDevelopment #LearningInPublic

@Primary & @Qualifier When multiple beans of the same type exist, confusion occurs. @Primary marks the default bean Spring should inject automatically. @Qualifier chooses the exact bean when multiple options exist. It provides precise dependency control during injection. Both avoid ambiguity and ensure stable configurations. #SpringFramework #Java #SoftwareEngineering #BackendDevelopment