Spring Security Challenges in Building a Secure REST API

🔥 Why Your Spring Boot App Returns 404 Even After Successful Startup ⸻ 1. Verify Controller Registration (Not Just Scanning) ➡️ Run with --debug and check auto-configuration logs ➡️ Use /actuator/mappings to confirm if endpoints are actually exposed ⚠️ If your endpoint is NOT listed → it’s not a routing problem, it’s a bean registration issue ⸻ 2. Package Structure (Classic Mistake) Spring Boot only scans downward from the main class package ✔️ Correct: com.app ├── Application.java ├── controller ❌ Wrong: com.app com.controller (won’t be scanned) ➡️ Fix with @ComponentScan if needed ⸻ 3. Annotation Issues (Very Common) ➡️ Missing @RestController or @Controller ➡️ Missing @RequestMapping, @GetMapping, etc. ➡️ Using @Controller without @ResponseBody → returns view instead of JSON → looks like 404 ⸻ 4. Context Path / Port Confusion Check: server.servlet.context-path=/api server.port=8081 Your endpoint becomes http://localhost:8081/api/hello ⚠️ Many devs hit /hello → get 404 → panic 😄 ⸻ 5. Spring Security Blocking Requests ➡️ If Spring Security is enabled: * Unauthenticated requests may not reach controller * Misconfigured rules can return 404 instead of 403 ✔️ Temporarily disable or allow all: http.authorizeHttpRequests().anyRequest().permitAll(); 6. DispatcherServlet Not Mapping Requests ➡️ Check if: spring.mvc.servlet.path Or custom servlet config is changing the routing 7. Static Resource Handler Overriding APIs ➡️ If WebMvcConfigurer is customized, static handlers might override API paths ⸻ 8. Wrong HTTP Method ➡️ Calling GET /users but API is @PostMapping("/users") ➡️ Spring returns 404 (not always 405 depending on config) ⸻ 9. Reverse Proxy / Gateway Issues (Production Case) ➡️ If behind: * Nginx * API Gateway Check if path rewriting is happening: /api/users → /users 10. Build / Deployment Mismatch ➡️ Old JAR running? ➡️ Controller added but not redeployed? ✔️ Always verify: ps -ef | grep java #engineering #development #springboot #java

Understanding HTTP Status Codes Today I focused on an important concept in backend development — HTTP Status Codes While building REST APIs, it’s not just about sending data, but also about sending the right response to the client. 🔹 Learned about different categories of status codes: • 2xx (Success) – 200 OK, 201 Created • 4xx (Client Errors) – 400 Bad Request, 404 Not Found • 5xx (Server Errors) – 500 Internal Server Error 🔹 Understood when to use each status code in real APIs 🔹 Implemented status handling using "ResponseEntity" in Spring Boot This helped me realize how APIs communicate clearly with frontend applications and handle errors properly. Small concept, but very powerful in building real-world applications. Next step: Improving API structure and adding more real-world logic. #Java #SpringBoot #BackendDevelopment #RESTAPI #CodingJourney

🚀 Day 17/100: Spring Boot From Zero to Production Topic: Activating Profiles in Spring Boot -> Why Activation Matters Creating profiles isn’t enough You need to activate them to use their config Otherwise, Spring Boot falls back to the default profile. -> Method 1: JVM Argument Pass this when running your app: -Dspring.profiles.active=dev Common for: Local development Switching configs quickly Loads application-dev.yaml -> Method 2: Environment Variable Set: SPRING_PROFILES_ACTIVE=dev Best for: Production environments CI/CD pipelines -> Default Behavior No active profile? default gets loaded Others are ignored Quick Insight Profiles = Config separation Activation = Making them work Simple concept. Powerful impact. This might sound simple but stay consistent. We’re building production mindset step by step. #Java #SpringBoot #SoftwareDevelopment #100DaysOfCode #Backend

🚨 Stop installing 15 packages just to start a Node.js API. I've built APIs with Express for years. It's battle-tested, flexible, and has a massive ecosystem. But here's the problem nobody talks about: Every new project starts the same way: → npm install cors helmet jsonwebtoken bcrypt swagger-ui-express... → Manually wiring app.use(require('./routes/users')) for every route → Bolting TypeScript on like an afterthought → Copy-pasting the same security middleware config (again) Sound familiar? That frustration is exactly why I built mimi.js — a production-ready Node.js framework that keeps Express's familiar API but ships with everything you actually need: ✅ Built-in JWT auth + bcrypt password hashing ✅ Auto route loading — just drop files into routes/ ✅ Auto Swagger docs from JSDoc comments ✅ Database adapters for MongoDB & SQLite ✅ Security headers, CORS, request logging — all built-in ✅ TypeScript-first, zero build step The goal wasn't to replace Express. It was to build the version of Express I wished existed when starting a new project. No 15-package install. No manual wiring. Just code. Over the next 6 days, I'll deep-dive into how it works — the routing engine, performance numbers, built-in features, and real-world use cases. 👇 Have you felt this pain too? Drop a comment — I'd love to hear your experience. 🔗 https://lnkd.in/gypGM-Y4 📦 npm install mimi.js #nodejs #javascript #typescript #webdevelopment #backend #expressjs #opensource #developer #programming #coding #softwareengineering #mimijs

Understanding CORS Errors (Simple Analogy) While working on backend APIs, I often faced CORS errors. It’s confusing at first because api works fine still we face issue, but simple when you relate it to real life. Think of your frontend and backend as two buildings, and the browser as security. You can access your own building freely, but entering another requires permission. Similarly, when your frontend (React/Angular) calls an API from a different origin (domain, port, or protocol), the browser blocks it unless the backend allows it. That’s where CORS configuration comes in. By adding allowed origins (e.g in Spring Boot), you’re telling the browser: This frontend is trusted. Without this: * Requests fail even if the API works fine * Errors appear in the browser, not backend logs Key learning: CORS is not a backend error — it’s a browser security feature. Understanding this helped me debug issues faster and avoid unnecessary backend changes. #SpringBoot #CORS #BackendDevelopment #WebDevelopment #WebSecurity #Java #APIs #FullStackDevelopment

Your Spring Boot app fails to start… ❌ No clear error. Just a long stack trace. And somewhere inside it… “𝗖𝗶𝗿𝗰𝘂𝗹𝗮𝗿 𝗱𝗲𝗽𝗲𝗻𝗱𝗲𝗻𝗰𝘆 𝗱𝗲𝘁𝗲𝗰𝘁𝗲𝗱” If you’ve seen this once, you’ll never forget the pain. Let’s simplify it What is a circular dependency? It’s when two (or more) classes 𝗱𝗲𝗽𝗲𝗻𝗱 𝗼𝗻 𝗲𝗮𝗰𝗵 𝗼𝘁𝗵𝗲𝗿. Example: @𝗦𝗲𝗿𝘃𝗶𝗰𝗲 𝗰𝗹𝗮𝘀𝘀 𝗔 {   𝗽𝗿𝗶𝘃𝗮𝘁𝗲 𝗳𝗶𝗻𝗮𝗹 𝗕 𝗯;   𝗽𝘂𝗯𝗹𝗶𝗰 𝗔(𝗕 𝗯) { 𝘁𝗵𝗶𝘀.𝗯 = 𝗯; } } @𝗦𝗲𝗿𝘃𝗶𝗰𝗲 𝗰𝗹𝗮𝘀𝘀 𝗕 {   𝗽𝗿𝗶𝘃𝗮𝘁𝗲 𝗳𝗶𝗻𝗮𝗹 𝗔 𝗮;   𝗽𝘂𝗯𝗹𝗶𝗰 𝗕(𝗔 𝗮) { 𝘁𝗵𝗶𝘀.𝗮 = 𝗮; } } Now Spring tries to create A → needs B Then creates B → needs A And it goes in circles… ♻️ Result? App won’t start. Why does this happen?  • Tight coupling between classes  • Poor separation of responsibilities  • Trying to make services do too many things How to debug it (simple way): Read the error message carefully 🔍 Spring actually tells you the dependency chain Identify the loop A → B → C → A Find the unnecessary dependency That’s usually the root cause How to fix it (real solutions): 🔹 1. Refactor your design (best solution) Break the dependency Example: Move shared logic into a third service A → C ← B (no more circular dependency) 🔹 2. Use 𝗰𝗼𝗻𝘀𝘁𝗿𝘂𝗰𝘁𝗼𝗿 𝗶𝗻𝗷𝗲𝗰𝘁𝗶𝗼𝗻 wisely (It actually helps detect the problem early) 🔹 3. Use @𝗟𝗮𝘇𝘆 (temporary fix) 𝗽𝘂𝗯𝗹𝗶𝗰 𝗕(@𝗟𝗮𝘇𝘆 𝗔 𝗮) { 𝘁𝗵𝗶𝘀.𝗮 = 𝗮; } This delays initialization… but don’t rely on it long-term. 🔹 4. Rethink responsibilities If two classes depend on each other, they probably shouldn’t be separate. 💡 Real insight Circular dependency is not just a Spring error… It’s a 𝗱𝗲𝘀𝗶𝗴𝗻 𝗽𝗿𝗼𝗯𝗹𝗲𝗺. Good architecture = fewer hidden loops Better code = easier debugging Next time your app refuses to start, don’t panic… Just ask: “Who depends on whom?” #SpringBoot #Java #BackendDevelopment #SoftwareEngineering #SpringFramework #JavaDevelopers #CircularDependency #SpringAnnotations #Microservices #SystemDesign #aswintech

🚀 Day 25/100: Spring Boot From Zero to Production Topic: Consuming REST APIs Making API calls to internal services or external providers used to be a headache. With Spring Boot, it’s a breeze. 🌬️ It only takes a few lines of code to handle the heavy lifting: Mark your class as a @Service to let Spring manage it. Use RestTemplate to handle the HTTP communication. Call methods like getForObject or postForEntity. Spring automatically deserializes the JSON response into your Java POJO. The New Standard: WebClient If you are building for production today, WebClient is the way to go. It’s part of the Spring WebFlux library and is built for the modern web. Non-Blocking: Your app doesn't sit idle waiting for a response. Versatile: It handles both synchronous and asynchronous communication perfectly. Better Performance: It can handle much higher concurrency with fewer system resources. #Java #SpringBoot #WebClient #100DaysOfCode #Backend

𝗦𝘁𝗼𝗽 𝘂𝘀𝗶𝗻𝗴 @ComponentScan 𝗳𝗼𝗿 𝘀𝗵𝗮𝗿𝗲𝗱 𝗺𝗼𝗱𝘂𝗹𝗲𝘀.⚡️ Your shared libraries should be 𝗽𝗹𝘂𝗴-𝗮𝗻𝗱-𝗽𝗹𝗮𝘆, not a guessing game of which beans are being scanned. 👉 The fix? 𝗔𝘂𝘁𝗼-𝗰𝗼𝗻𝗳𝗶𝗴𝘂𝗿𝗮𝘁𝗶𝗼𝗻. Clean. Predictable. Zero setup. I wrote a quick guide on how to do it right in Spring Boot 👇 https://lnkd.in/dAu6mrtG #SpringBoot #Beans #Java #Kotlin #SoftwareArchitecture

Most developers return wrong HTTP status codes. Here's the correct way 👇 I see this mistake constantly in code reviews: return ResponseEntity.ok(null); // ❌ Wrong for errors return ResponseEntity.ok("User deleted"); // ❌ Wrong for DELETE The correct way: ✅ 200 OK — GET request success, data returned ✅ 201 CREATED — POST success, resource created ✅ 204 NO CONTENT — DELETE success, nothing to return ✅ 400 BAD REQUEST — Invalid input from client ✅ 401 UNAUTHORIZED — Not logged in ✅ 403 FORBIDDEN — Logged in but no permission ✅ 404 NOT FOUND — Resource doesn't exist ✅ 409 CONFLICT — Duplicate data (email already exists) ✅ 500 INTERNAL SERVER ERROR — Something broke on server Spring Boot example: return ResponseEntity.status(HttpStatus.CREATED).body(savedUser); Correct status codes make your API professional, predictable, and frontend-developer friendly. Save this. Share with your team. Which status code do you see misused most? 👇 #SpringBoot #RestAPI #Java #BackendDevelopment #APIDesign

Authentication doesn’t have to be a "Black Box." 📦✨ When I first started in backend development, "JWT" sounded like just another scary acronym. But once you understand the flow, everything clicks. If you are building your first Full-Stack app, you’ve probably asked: "Once a user logs in, how does the server know who they are on the next page?" The infographic below is the perfect "Cheat Sheet" for your journey. Here is the "Junior-to-Pro" breakdown: 🔹 The Handshake: You give the server your email/password. It checks its database. 🔹 The Passport: Instead of keeping you "on the line," the server hands you a signed JWT. Think of this as a digital passport. 🔹 The Payload: That token isn't just random letters. It contains your User ID and permissions, but it’s encoded so it’s compact. 🔹 The Request: Every time you want to see your profile or post a comment, you show that passport in the Authorization header. 🔹 The Validation: The server doesn't need to look you up in the DB again. It just checks the Signature. If the signature is valid, you're in! 🔓 Why should you care? In a world of Microservices, JWTs are the gold standard. They make your apps faster and easier to scale because the server stays "stateless." Pro-Tip for the road: 💡 Never put sensitive info (like passwords) inside the JWT payload. Anyone can decode it! It’s for identification, not for secrets. Did this help clear up the JWT mystery? Hit that Like 👍 if you want more simplified "System Design" breakdowns like this! 🚀 #JuniorDeveloper #LearningToCode #Java #SpringSecuriy #SpringBoot #OAuth #WebDevelopment #CodingTips #SoftwareEngineering #JWT #BackendTips