Spring Dependency Injection: Setter vs Constructor

What happened when run the code ? @RestController public class TestController { @Autowired private TestService testService; public TestController() { System.out.println(testService.getMessage()); } } Looks correct but throw error ? Answer: NullPointerException Why : spring inject dependencies after constructer execution so testService is null inside constructer #Spring flow is: 1. Object is created (constructor runs first) 2. Then dependency injection happens (@Autowired) #SpringBoot #Java #Backend #CodingInterview #FAANG #Microservices #Programming #Developers

🧠 Real Microservices Use Case 👉 Service A calls Service B ❌ RestTemplate Thread waits → poor scalability ✅ WebClient Async call → handles more requests ⚙️ Production Best Practices With WebClient: Use connection pooling Add timeout Handle retries Add Resilience (Important) Combine with: Retry Circuit Breaker (using Resilience4j) #Java #JavaDeveloper #SpringBoot #Microservices #WebClient #RestTemplate #BackendDevelopment #SoftwareEngineering #SystemDesign #TechInterview #Programming #Developers #Coding #CloudComputing

💫@𝐏𝐫𝐢𝐦𝐚𝐫𝐲 𝐯𝐬 @𝐐𝐮𝐚𝐥𝐢𝐟𝐢𝐞𝐫 𝐢𝐧 𝐒𝐩𝐫𝐢𝐧𝐠 𝐁𝐨𝐨𝐭: When working with dependency injection in Spring Boot, handling multiple beans of the same type can get tricky. That’s where @Primary and @Qualifier come into play 👇 👉 @Primary Used to define a default bean. If multiple beans exist, Spring automatically picks the one marked as @Primary. 👉 @Qualifier Used to explicitly specify which bean you want. Gives you precise control over dependency injection. 💡 Key Insight: Use @Primary for default behavior and @Qualifier when you need specific control. Together, they make your code more flexible and maintainable. #SpringBoot #JavaDeveloper #BackendDevelopment #DependencyInjection #SpringFramework #Java #Coding #SoftwareDevelopment #TechLearning #Developers #Programming #100DaysOfCode #JavaBackend #SpringAnnotations 𝐓𝐡𝐚𝐧𝐤𝐬 𝐭𝐨 𝐦𝐲 𝐌𝐞𝐧𝐭𝐨𝐫: Anand Kumar Buddarapu Saketh Kallepu Uppugundla Sairam

Is your design really SOLID… or just working for now? Most systems don’t fail because of bad syntax—they fail because they’re rigid, tightly coupled, and impossible to evolve. The Interface Segregation Principle forces a powerful shift: stop depending on bulky, do-everything contracts and start designing small, focused interfaces that give you true flexibility, cleaner tests, and effortless change. When your code depends on behavior—not implementations—you unlock systems that scale without breaking. The real question is: can your design handle tomorrow’s requirements without a rewrite? https://lnkd.in/eRJTKMch #Java #SOLIDPrinciples #CleanCode #SoftwareDesign #SystemDesign #ObjectOrientedProgramming #OOP #InterfaceSegregation #DesignPatterns #CodingBestPractices #DeveloperMindset #ScalableSystems #TechLeadership #Programming #JavaDeveloper

schedule tasks in Spring Boot using the powerful @Scheduled annotation and Cron expressions. In this complete guide, you will understand fixedRate, fixedDelay, and cron-based scheduling with real-world examples like email automation and background jobs. #SpringBoot #CronJobs #Java #BackendDevelopment #FullStackDeveloper #Programming #JavaDeveloper #Coding #SoftwareDevelopment #TechTutorial

Find the minimum distance between a given start index and any occurrence of a target in the array. Leetcode problem link: https://lnkd.in/gZFkirHw 🔍 Key Takeaways: Used a two-pointer approach to scan from both ends. Kept updating the minimum absolute distance from start. Included the condition left != right to avoid checking the same element twice. ✅ Why this works: Instead of scanning only from one side, this approach checks both ends in each iteration, making the logic structured and efficient. 📘 What I like about this solution: Simple and readable Avoids redundant checks Great example of combining two pointers with distance calculation #Java #LeetCode #DSA #Programming #SoftwareEngineering #Developers #loveToCode

A common confusion in Spring Boot: @Primary vs @Qualifier Which one takes priority? - @Primary defines a default bean - @Qualifier explicitly specifies the exact bean When both are used, @Qualifier overrides @Primary Key takeaway: Explicit configuration always wins over default behavior. This is a frequently asked concept in Spring interviews and critical for writing predictable dependency injection code. What’s your approach when handling multiple beans? #SpringBoot #Java #BackendDevelopment #CodingInterview #SoftwareDevelopment #Programming #Developers

💫 𝐔𝐧𝐝𝐞𝐫𝐬𝐭𝐚𝐧𝐝𝐢𝐧𝐠 𝐓𝐲𝐩𝐞𝐬 𝐨𝐟 𝐃𝐞𝐩𝐞𝐧𝐝𝐞𝐧𝐜𝐢𝐞𝐬 𝐢𝐧 𝐒𝐩𝐫𝐢𝐧𝐠 𝐅𝐫𝐚𝐦𝐞𝐰𝐨𝐫𝐤 Today I explored one of the core concepts of the Spring Framework — Dependency Injection and its types. 🔹 𝐏𝐫𝐢𝐦𝐢𝐭𝐢𝐯𝐞 𝐃𝐞𝐩𝐞𝐧𝐝𝐞𝐧𝐜𝐲 Injecting simple values like int, String, boolean directly into objects. 🔹 𝐂𝐨𝐥𝐥𝐞𝐜𝐭𝐢𝐨𝐧 𝐃𝐞𝐩𝐞𝐧𝐝𝐞𝐧𝐜𝐲 Injecting a group of values using collections like List, Set, Map, etc. 🔹 𝐑𝐞𝐟𝐞𝐫𝐞𝐧𝐜𝐞 𝐃𝐞𝐩𝐞𝐧𝐝𝐞𝐧𝐜𝐲 Injecting one object into another — the heart of Spring DI, enabling loose coupling and scalable design. 💡 Key Insight: While primitive and collection dependencies handle data, reference dependency is what truly powers real-world applications. Understanding these concepts helps in building clean, maintainable, and loosely coupled applications — which is exactly what modern development demands. #SpringFramework #JavaDeveloper #DependencyInjection #BackendDevelopment #Java #SpringBoot #Programming #SoftwareEngineering #Coding #TechLearning #Developers #LinkedInLearning 𝐓𝐡𝐚𝐧𝐤𝐬 𝐭𝐨 𝐦𝐲 𝐌𝐞𝐧𝐭𝐨𝐫 : Anand Kumar Buddarapu Saketh Kallepu Uppugundla Sairam

🚀 Understanding Autowiring in Spring + Key Difference: byName vs byType In Spring Framework, Autowiring simplifies dependency injection by automatically connecting beans without explicit configuration. Instead of manually writing <property> or <constructor-arg>, Spring intelligently injects dependencies for us — saving time and reducing boilerplate code. 💡 Two commonly used Autowiring modes: 🔹 byName Matches the bean id with the property name Works only if names are exactly the same Example: property engine → bean id must be engine 🔹 byType Matches based on the data type of the property Automatically injects the bean of that type ⚠️ Fails if multiple beans of the same type exist 📊 Quick Comparison: ✔ byName → depends on naming convention ✔ byType → depends on class/type matching 🎯 When to use what? Use byName when naming is consistent and controlled Use byType when working with clear, unique bean types 👉 In modern development, annotation-based autowiring (@Autowired) is more commonly used for flexibility and cleaner code. Thanks Anand Kumar Buddarapu #Java #SpringBoot #DependencyInjection #Autowiring #BackendDevelopment #Programming

👋 Hello LinkedIn Network! Ever looked at your code and thought, “Oh no, it’s a total mess!” 😅 Don’t worry, it happens to everyone.Want to write cleaner, more maintainable Java code? Understanding the SOLID principles is a game-changer. Here's a quick cheat sheet: 🔹 S — Single Responsibility Principle One class → one responsibility 🔹 O — Open/Closed Principle Extend behavior without modifying existing code 🔹 L — Liskov Substitution Principle Child classes must behave like parent 🔹 I — Interface Segregation Principle Use small, specific interfaces 🔹 D — Dependency Inversion Principle Depend on interfaces, not concrete classes 💡 Applying these principles helps you build flexible systems that are easier to test, debug, and scale. 🚀 Try using SOLID in your next project and notice the difference! #Java #CleanCode #SOLIDPrinciples #SoftwareEngineering #Programming #Developers