Spring Proxying: Understanding Singleton Behaviour in @Configuration Classes

𝗦𝗽𝗿𝗶𝗻𝗴 𝗕𝗼𝗼𝘁 𝗟𝗲𝗮𝗿𝗻𝗶𝗻𝗴 𝗝𝗼𝘂𝗿𝗻𝗲𝘆 — 𝗗𝗮𝘆 𝟯 Day 3 was where things started getting more real. This section focused on the core concepts of the Spring Framework — the things that actually make Spring powerful behind the scenes. The total duration was around 2 hours 18 minutes, but again, it took me 1 week to properly understand and connect everything. Here’s what I learned: 🔹 What a Web Framework is 🔹 Introduction to Spring Framework 🔹 Tight Coupling vs Loose Coupling (with hands-on) 🔹 Core concepts of Spring (Java Web Development basics) 🔹 Spring Container & Configuration 🔹 Setting up a Spring project 🔹 Beans in Spring • Creating your first Bean • Bean Lifecycle 🔹 Dependency Injection (DI) • Constructor Injection • Setter Injection 🔹 Inversion of Control (IoC) 🔹 Autowiring • By Name • By Type • By Constructor Understanding concepts like Dependency Injection and IoC really changed how I think about writing code. It’s less about creating everything manually and more about letting Spring manage things efficiently. Also, concepts like loose coupling finally started making practical sense when I saw them in code. 📌 Next part coming soon. #SpringBoot #JavaDeveloper #BackendDevelopment #LearningJourney #Day3 #TechGrowth #Consistency

🚀 30 Days of Spring Boot – Day 2 Today I explored one of the core foundations of Spring — Beans & Their Management. 🔹 What I learned: ✅ Spring Bean A Bean is a Java object managed by the Spring IoC container. Instead of creating objects using new, Spring handles creation, lifecycle, and dependency injection. ✅ @Bean Annotation Used to manually define a Bean inside a @Configuration class. It gives full control over object creation — especially useful for third-party classes or custom configurations. 💡 Even though we use new inside a @Bean method, it is executed only once by Spring (Singleton scope by default) and reused across the application. ✅ Bean Scope Defines how many instances Spring creates: Singleton → Single shared instance (default) Prototype → New instance every time Request → Per HTTP request Session → Per user session 🔥 Key Takeaway: “Write new once, let Spring manage and reuse the object everywhere.” 📌 Strengthening fundamentals step by step. #SpringBoot #Java #BackendDevelopment #LearningJourney #100DaysOfCode #Microservices

The @Transactional Proxy Pitfall Think slapping @Transactional on a method guarantees database rollback on failure? Think again. 🚨 One of the most common critical bugs I see in Spring Boot applications isn't a logic error—it's a misunderstanding of how Spring AOP (Aspect-Oriented Programming) works under the hood. Enter the Self-Invocation Problem. If you have a non-transactional method processOrder() that calls a @Transactional method saveToDatabase() within the exact same class, that transaction will never start. If an exception is thrown, your data will not roll back. 💥 Why does this happen? Spring manages transactions using proxies. When an external class calls your bean, it hits the proxy first, which starts the transaction. But when you make an internal method call (calling this.saveToDatabase()), you are bypassing the proxy entirely and calling the raw object. No proxy = no transaction. How to fix it: 1️⃣ Refactor: Move the @Transactional method to a separate dedicated Service class (Best Practice). 2️⃣ Self-Injection: Inject the class into itself using @Autowired or constructor injection, and call the method via the injected instance. 3️⃣ AspectJ: Switch from proxy-based AOP to AspectJ weaving (Heavyweight, but solves proxy limitations). Understanding the framework's internal mechanics is the difference between writing code that compiles and writing systems that are truly fault-tolerant. Have you ever been bitten by the Spring proxy self-invocation trap? What is your favorite obscure Spring Boot "gotcha"? Let's geek out in the comments! 👇 Tags: #Java #SpringBoot #SoftwareEngineering #BackendDevelopment #AdvancedJava #SystemDesign #CodingTips

💡 Spring Boot in 2026: The Architecture Shift You Can’t Ignore. If you’ve ever worked with backend systems, you’ve probably seen this evolution: ❌ On the left: the “old pain” Controllers, services, and repositories tightly wired together. Manual dependencies everywhere. Hard to test, harder to scale, and one small change can break everything. Classic fragile architecture. 🧠 In the middle: the real game changer Spring’s IoC Container + Dependency Injection. Instead of you managing dependencies, Spring takes over and injects exactly what each part needs. Clean separation. Fully testable. Much less chaos. ✅ On the right: the ideal world Controller → Service → Repository flowing smoothly. No tight coupling. No messy wiring. Just clean, maintainable, scalable architecture. 💡 The real takeaway: In modern backend development, architecture matters more than syntax. Writing code is easy — building systems that survive real-world scale is the real skill. Spring Boot didn’t just simplify Java development. Be honest — which side did you start your journey on? 😄 #SpringBoot #Java #BackendDevelopment #SystemDesign #SoftwareArchitecture #DependencyInjection #CodingLife

Just wrapped up a take home assessment where I built an LRU (Least Recently Used) Cache from scratch in Java, and I decided to take it a step further. Instead of stopping at the basic implementation, I: • Designed it using a combination of HashMap and Doubly LinkedList to achieve O(1) time complexity for both get and put operations • Applied generics to make the cache reusable and type-safe • Extended it into a Spring Boot REST API to simulate real world backend usage • Recorded a walkthrough loom video explaining my design decisions and trade-offs. This exercise was a good reminder that writing code is only one part of the job, being able to clearly explain "WHY" you made certain decisions is just as important. Key takeaway: Clean design + clear communication > just “working code”. Looking forward to more opportunities to build and share. #Java #BackendDevelopment #SystemDesign #SpringBoot #SoftwareEngineering #LRUCache

Spring doesn’t just create beans- it manages their entire lifecycle. Many developers stop at "@Autowired", "@Qualifier", and "@Primary". But to build reliable and production-ready applications, understanding the Spring Bean Lifecycle is essential. ------ 🧠 What happens behind the scenes? A Spring bean goes through multiple stages: • Instantiation • Dependency Injection • Initialization (e.g., "@PostConstruct") • Ready for use • Destruction (e.g., "@PreDestroy") ------ 🔥 Key idea: • "@PostConstruct" → Used for initialization after dependencies are injected • "@PreDestroy" → Used for cleanup before the bean is destroyed ----- 💡 Why this matters: Proper lifecycle management helps you: ✔ Avoid resource leaks ✔ Manage connections effectively ✔ Write cleaner and more maintainable code ✔ Build stable, production-ready applications ----- 🎯 Best practice: Avoid placing heavy logic (such as database calls) inside constructors. Instead, use lifecycle annotations to handle initialization and cleanup in a structured way. ----- 📌 Takeaway: If your Spring knowledge ends at dependency injection, you’re only scratching the surface. 👉 Understanding the lifecycle is what separates good developers from great ones. #SpringBoot #SpringFramework #JavaDeveloper #BackendDevelopment #SoftwareEngineering #CleanCode #CodingBestPractices #LearnInPublic #Developers #Java

How Ioc Container of Spring Boot Works? Today, I deepened my understanding of how the IoC (Inversion of Control) container works in Spring Boot. The IoC container is the core of Spring’s dependency management system—it takes over the responsibility of creating, managing, and injecting objects (beans) in an application. Instead of manually instantiating objects, the container automatically wires dependencies, which allows developers to write cleaner and more maintainable code. Beans can be defined using annotations like @Component, @Service, @Repository, or via @Configuration and @Bean, and the container ensures their proper initialization and lifecycle management. What fascinated me is how Spring Boot handles everything behind the scenes: it scans packages for components, registers them as bean definitions, resolves dependencies, and manages scopes such as singleton, prototype, or request-scoped beans. It also provides hooks for bean post-processing and lifecycle events like @PostConstruct and @PreDestroy. This system not only reduces boilerplate code but also enables features like testing with mocks, AOP (aspect-oriented programming), and flexible configuration, making the development of complex applications much more manageable. Learning the internal workings of the IoC container gave me a much clearer picture of how Spring Boot promotes decoupled, modular, and maintainable design, which is essential for building scalable Java applications. #SpringBoot #Java #OOP #DependencyInjection

Day 4: Diving into the Heart of Spring Framework – The Core Module & IoC Container 🚀 I am officially four days into my Spring Framework learning journey, and today was all about understanding the "brain" behind the magic: the Spring Core Module. If you are just starting out, here is a quick breakdown of the foundational concepts I covered today that are essential for any backend developer: 🔹 What is Spring Core? It is the base module of the entire Spring ecosystem. It provides the fundamental parts of the framework, including the IoC (Inversion of Control) Container, which is responsible for managing the lifecycle of objects, known as Spring Beans. 🔹 The Magic of IoC (Inversion of Control) In standard Java, we (the programmers) create and manage objects manually. In Spring, we hand that control over to the container. The container handles: Bean Lifecycle Management: Creating, initializing, and destroying objects. Dependency Injection (DI): Automatically providing the objects (dependencies) a class needs to function. 🔹 BeanFactory vs. ApplicationContext I learned that there are two main types of IoC containers: BeanFactory: The basic, lightweight container (mostly used for mobile/low-resource apps). ApplicationContext: The advanced container used in most modern applications. It includes everything BeanFactory has plus extra features like internationalization and easier integration with Spring AOP. 🔹 Flexible Configuration Spring is incredibly flexible in how you "tell" the container to manage your beans. We explored: XML-Driven: The traditional way using external files. Annotation-Driven: Using tags like @Component and @Autowired directly in the code. Java-Code-Driven: Using Java classes marked with @Configuration to define bean logic. Understanding these core principles is a game-changer for writing decoupled, testable, and maintainable code. Are you also learning Spring? What was your "Aha!" moment with Dependency Injection? Let’s connect and grow together! 👇 #SpringFramework #JavaDevelopment #BackendDeveloper #LearningJourney #SoftwareEngineering #SpringCore #IoC #DependencyInjection #CodingCommunity #JavaProgramming #WebDevelopment