5 Common Spring Boot Mistakes to Avoid

🚀 Day 20/100: Spring Boot From Zero to Production Topic: Custom Auto-Configuration We covered Auto-Configuration. We covered disabling it. But does it stop there? Nope. 👀 Spring Boot lets you build your own auto-configuration too. 🔧 But, How It Works? You create a @Configuration class and slap conditionals on it. Spring Boot only loads it if your conditions are met. Two most common ones: @ConditionalOnClass → Load only if a class exists on the classpath @ConditionalOnProperty → Load only if a property is set in application.properties 💡 See the code attached below. ⬇️ No DataSource on classpath? → Skipped entirely db.enabled=false? → Skipped entirely Bean already defined by user? → Your default is skipped ✅ 📌 Don't forget to register it In META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports: -> com.yourpackage.MyDataAutoConfiguration Without this, Spring Boot won't pick it up. Checkout the previous posts on Auto-Config & disabling it to better understand the sequence. See you in the next one! #Java #SpringBoot #SoftwareDevelopment #100DaysOfCode #Backend #AutoConfiguration

Most people use Spring Boot. But very few understand what actually happens when the application starts While going deeper into it, a few things started making more sense How the application context is created What SpringBootApplication really triggers How the bean lifecycle actually works Why proxies are used for things like Transactional And how self invocation can silently break things It is easy to write Spring code Understanding what happens inside is different Still learning and connecting the dots What part of Spring feels confusing to you #Java #SpringBoot #BackendDevelopment #SoftwareEngineering #JavaDeveloper #SystemDesign #Placements

⚙️ One Spring Boot Practice That Changed My Code Quality I stopped using field injection. ❌ @Autowired on fields ✅ Constructor Injection Why? ✔ Better testability ✔ Immutable dependencies ✔ Cleaner design Small change… big impact. If you’re still using field injection — try this once. What’s your preferred approach? 🤔 #SpringBoot #Java #BestPractices

I used to think Spring Boot just runs and handles everything Swipe to see what is actually happening inside If your answer to how Spring Boot works is it just runs and handles requests you are probably missing what actually matters Most people can build with Spring Boot very few understand what happens under the hood While going deeper, a few things started making more sense • How the application starts and builds the context • What SpringApplication triggers behind the scenes • How beans are created and managed step by step • Why proxies exist and where they actually matter • How self invocation can silently break transactions The more I learn, the more I realise it is not just about writing code it is about understanding how the system behaves Still learning, but this changed how I approach backend development What part of Spring Boot internals do you find confusing #Java #SpringBoot #BackendDevelopment #SoftwareEngineering #SystemDesign

🥤 𝕊𝕡𝕣𝕚𝕟𝕘 𝕧𝕤 𝕊𝕡𝕣𝕚𝕟𝕘 𝔹𝕠𝕠𝕥 — 𝕋𝕙𝕚𝕟𝕜 𝕠𝕗 𝕚𝕥 𝕝𝕚𝕜𝕖 𝕥𝕙𝕚𝕤 When I first learned backend development, i thought Spring and Spring Boot were basically the same thing.. They’re not. And this small confusion can slow you down more than you think. Let’s simplify it 👇 : 🧰 𝗦𝗽𝗿𝗶𝗻𝗴 𝗙𝗿𝗮𝗺𝗲𝘄𝗼𝗿𝗸 Gives you all the tools you need: Dependency injection. Configuration. Flexibility. Full control. 👉 But… you have to assemble everything yourself. ⚡ 𝗦𝗽𝗿𝗶𝗻𝗴 𝗕𝗼𝗼𝘁 Takes those same tools and says: “Let me set things up for you.” Auto-configuration. Embedded server. Minimal setup. Production-ready faster. 💡 𝐓𝐡𝐞 𝐝𝐢𝐟𝐟𝐞𝐫𝐞𝐧𝐜𝐞 𝐢𝐧 𝐨𝐧𝐞 𝐬𝐞𝐧𝐭𝐞𝐧𝐜𝐞: 👉 Spring = control. 👉 Spring Boot = speed. Now here’s what many developers miss: Using Spring Boot without understanding Spring is like using a machine.. without knowing how it works. It works fine — until something breaks. That’s why strong backend engineers: ✔️ Use Spring Boot for productivity. ✔️ Understand Spring for control. The goal is not to choose one over the other. It’s to use both — the right way. #Java #Spring #SpringBoot #BackendDevelopment #SoftwareEngineering #Microservices #Programming #JavaDeveloper

⚔️ Spring vs Spring Boot Spring Framework 🔹 Requires manual configuration 🔹 More control and flexibility 🔹 Takes more setup time Spring Boot 🔹 Auto-configuration (less setup) 🔹 Embedded server (no need to deploy separately) 🔹 Faster development 💡 In short: Spring Boot is built on top of Spring to make development quicker and easier. 👉 Use Spring Boot for rapid development 👉 Use Spring when you need full control #Java #SpringFramework #SpringBoot #BackendDevelopment #Coding

🚀 What really happens when you run a Spring Boot application? Most developers use: 👉 SpringApplication.run(App.class, args); …but few understand what happens behind the scenes. Here’s a clear breakdown: 🔹 1. Bootstrapping Starts The JVM calls main(), and Spring Boot begins initialization. 🔹 2. Environment Setup Loads application.properties / application.yml, environment variables, and profiles. 🔹 3. ApplicationContext Creation Spring creates the IoC container to manage all beans. 🔹 4. Component Scanning Detects @Component, @Service, @Repository, @RestController and registers them. 🔹 5. Auto-Configuration Based on dependencies, Spring Boot configures components automatically (MVC, JPA, etc.). 🔹 6. Embedded Server Startup Starts embedded Apache Tomcat—no external installation needed. 🔹 7. DispatcherServlet Initialization Registers the front controller to handle all incoming HTTP requests. 🔹 8. Bean Initialization & Dependency Injection All beans are created and wired using DI. 🔹 9. Application Ready ✅ Your app is now ready to handle requests. 💡 Key Takeaway: SpringApplication.run() is not just a method—it bootstraps the entire application, sets up the container, auto-configures components, and starts the web server. #Java #SpringBoot #BackendDevelopment #Microservices #Programming #SoftwareEngineering #TechLearning

Spring Boot 4.1.0-M4 is out now and if you are using M3 there is something you should know. They changed their mind about the RabbitMQ updates. So if you made changes to those settings you need to change them Also that problem where the application.properties file was not working right? It is fixed now. Now let us look at the picture. Spring Boot 4 is like a new beginning. It uses Spring Framework 7. It needs JDK 17 to work. It also has some features like trying again if something fails and it is safer when dealing with empty values. It even supports versions of REST without needing extra work. If you are still using Boot 3.x do not worry. They also released 3.5.13 on the day. You are not behind. If you are starting a new project in 2026 Spring Boot 4 is the way to go. You should start reading the guide on how to move to Boot 4 before your team tells you to do it when you're, in a hurry. #SpringBoot #Java #BackendDevelopment #FullStackDeveloper #SoftwareEngineering #JavaDeveloper #REST #SpringFramework #Microservices #Coding #SoftwareDeveloper #TechNews #OpenSource #DeveloperLife

Most developers use Spring… but don’t fully understand what it’s actually doing under the hood. Here’s the reality 👇 Earlier, we used to create objects manually using new. That means we controlled everything — object creation, dependency wiring, lifecycle. But that approach leads to: ❌ Tight coupling ❌ Hard-to-test code ❌ Difficult maintenance Spring flips this completely. Instead of us controlling objects, Spring takes control — this is Inversion of Control (IoC). Now the container: ✔ Creates objects ✔ Injects dependencies ✔ Manages lifecycle And this is where Dependency Injection (DI) comes in. From experience and best practices: Constructor Injection → most reliable (preferred) Setter Injection → useful but optional Field Injection → avoid in real projects Another thing many people ignore is the Bean Lifecycle. A Spring Bean is not just created and used — it goes through: ➡ Creation ➡ Dependency Injection ➡ Initialization (@PostConstruct) ➡ Proxy wrapping (like @Transactional) ➡ Destruction (@PreDestroy) Understanding this is what separates: 👉 Someone who “uses Spring” vs 👉 Someone who can debug, design, and scale Spring applications If you're working on real-world backend systems, this is not optional knowledge. This is the foundation. #Spring #SpringBoot #Java #Backend #Microservices #IoC #DependencyInjection

🚨 Spring Boot is NOT Magic — Here’s What Actually Happens Many developers use Spring Boot daily… But can’t explain what happens behind this line: 👉 @SpringBootApplication Let’s break the “magic” 🔥 That single annotation actually does 3 things: ✅ @Configuration → Defines beans ✅ @EnableAutoConfiguration → Auto-configures based on classpath ✅ @ComponentScan → Scans your packages for components 💡 The real power is in Auto-Configuration Spring Boot checks: 👉 What dependencies are present? 👉 What beans are missing? Then it automatically configures things for you. Example: If spring-boot-starter-web is present → ✔ DispatcherServlet is configured ✔ Embedded server (Tomcat) starts ✔ MVC config is applied ⚠️ Where most candidates struggle: They say: ❌ “Spring Boot automatically does everything” But can’t explain: 👉 How beans are created 👉 How conditions work (@Conditional) 👉 How to override default configs 🎯 What strong engineers know: • How AutoConfiguration classes work • How Spring decides which bean to create • How to debug startup issues (logs, conditions report) 🔥 Interview Tip: Next time someone asks “How Spring Boot works?” Don’t say “auto configuration happens” Say: 👉 “Spring Boot uses conditional auto-configuration based on classpath and bean context” #springboot #java #backend #microservices #softwareengineering #interviewprep #techlearning