RajKumar Prasad’s Post

Spring Boot @Primary — Resolve multiple bean conflicts ⚡ Ever seen this error? “No qualifying bean of type found” ❌ Happens when: 👉 Multiple beans of same type exist Solution 👇 @Primary public class MyServiceImpl implements MyService {} 💡 What it does: Marks default bean when multiple exist Alternative: 👉 Use @Qualifier ⚠️ Mistake: Not handling multiple beans properly 👉 Leads to runtime errors Clean DI = stable application 🔥 #SpringBoot #Java #DependencyInjection

Spring Boot HandlerExceptionResolver — Advanced error handling 🔥 Most devs use @ControllerAdvice… but there’s a deeper layer 👇 👉 HandlerExceptionResolver It gives full control over: ✔ Exception handling ✔ HTTP response ✔ Error mapping 💡 Why use it? ✔ Fine-grained control ✔ Custom framework-level handling ⚠️ Use case: When @ExceptionHandler is not enough 👉 Example: Handle all exceptions globally with custom logic This is how frameworks are built internally 💯 #SpringBoot #Java #ExceptionHandling

What is @RestController in Spring Boot? 🚀 It is a combination of: @Controller + @ResponseBody 👉 It directly returns JSON response Example: @RestController public class Test {   @GetMapping("/hello")   public String hello() {     return "Hello";   } } Simple, clean, and perfect for APIs. Are you using Spring Boot in your project? #SpringBoot #Java #BackendDeveloper

The main class is the entry point  of the Spring Boot application. It contains  the @SpringBootApplication annotation and  starts the embedded  server using SpringApplication.run().. . . . . . . . . . #Java #JavaProgramming #JavaDeveloper #JavaCode #JavaScript #JavaCommunity #JavaTutorial #JavaLearning #JavaDevelopment #JavaLife #JavaLovers #JavaProjects #JavaCoding #JavaTips #JavaFramework #Java8 #JavaEE #JavaForBeginners #JavaGeek #JavaWorld #hackforge

Spring Boot @Bean vs @Component — Hidden difference 🔥 Both create beans… but NOT the same 👇 ✅ @Component - Auto-detected via component scan - Used for your own classes ✅ @Bean - Defined manually inside @Configuration - Used for third-party classes Example: @Bean public ObjectMapper objectMapper() { return new ObjectMapper(); } 💡 Why it matters: ✔ Better control over bean creation ✔ Custom configuration 👉 Use @Bean when you need flexibility Small concept → big design impact 💯 #SpringBoot #Java #Backend

🚀 Using Resilience4j with Spring Boot (Java) To use Resilience4j in a Spring Boot application, include the `resilience4j-spring-boot2` dependency. Annotate your methods with `@CircuitBreaker` to enable the circuit breaker functionality. Configure the circuit breaker properties in your `application.properties` or `application.yml` file, such as the failure rate threshold, the slow call rate threshold, and the wait duration in open state. This allows you to control the behavior of the circuit breaker. #Java #JavaDev #OOP #Backend #professional #career #development

#java #springboot #tips 🚫 Stop using field injection in Spring Boot. Here’s why: Most developers write this: @Autowired private UserService userService; ✅ Use constructor injection instead: @Service @RequiredArgsConstructor public class OrderService { private final UserService userService; // immutable + testable } Why it matters: • Fields are final → truly immutable • Easier to unit test without Spring context • Fails fast at startup if bean is missing • Works perfectly with Lombok’s @RequiredArgsConstructor This is also the official Spring recommendation since Spring 4.x. #Java #SpringBoot #CleanCode #BackendDev

Spring Boot Custom Argument Resolver 🚀 Want to inject custom objects into controller automatically? You can 👇 public class UserArgumentResolver implements HandlerMethodArgumentResolver { @Override public boolean supportsParameter(MethodParameter parameter) { return parameter.getParameterType().equals(User.class); } @Override public Object resolveArgument(...) { return getUserFromToken(); } } 💡 Use case: ✔ Extract user from JWT ✔ Avoid repeated code in controllers 👉 Clean & powerful approach 🔥 Real-world: Used in production for authentication context This is advanced Spring Boot design 💯 #SpringBoot #Java #Backend

⚙️ 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

🚀 Spring Boot Tip: @Qualifier vs @Primary (Fix Bean Ambiguity) Facing this error? 👇 "NoUniqueBeanDefinitionException" 👉 It means Spring found multiple beans of the same type and doesn’t know which one to inject. --- ✅ @Qualifier — Be Explicit Use "@Qualifier" when you want to specifically choose a bean. @Autowired @Qualifier("upiPaymentService") private PaymentService paymentService; ✔ You tell Spring exactly which implementation to inject ✔ Best when you have multiple beans and need control --- ✅ @Primary — Set a Default Use "@Primary" to mark one bean as the default choice. @Component @Primary class CreditCardPaymentService implements PaymentService {} ✔ Spring will pick this automatically ✔ Works when no "@Qualifier" is specified --- 🧠 Key Difference 👉 "@Qualifier" = Explicit selection 👉 "@Primary" = Default fallback --- ✨ Pro Tip If both are present: ➡️ "@Qualifier" overrides "@Primary" --- #SpringBoot #Java #BackendDevelopment #CodingTips #SoftwareEngineering