Spring Boot PATCH API with ReflectionUtils

@Autowired & @Qualifier in Spring Framework 👇 In the Spring Framework, @Autowired and @Qualifier are used for Dependency Injection. 🔹 @Autowired @Autowired is used to automatically inject dependencies into a class. The Spring IoC container finds and connects the required bean without manually creating objects using new. ✅ Why use @Autowired? Reduces boilerplate code Removes manual object creation Supports loose coupling Makes code cleaner and more readable 📌 Where can we use @Autowired? On Constructor (Recommended ✅) On Setter methods On Fields 🔹 @Qualifier @Qualifier is used along with @Autowired when multiple beans of the same type exist. It helps Spring identify which exact bean should be injected. ✅ Why use @Qualifier? Resolves ambiguity Provides better control over bean selection Makes configuration more precise 📌 Where can we use @Qualifier? In class-based (annotation-based) configuration On Constructor parameters On Setter methods On Fields 👉 In simple words: @Autowired performs injection @Qualifier selects the correct bean Together, they make Spring applications clean, flexible, and well-structured. 📚 Currently learning & implementing concepts step by step. #Spring #Autowired #Qualifier #DependencyInjection #IOC #SpringFramework #Java #BackendDevelopment #JavaFullStack #Day13_Adv_Java

⏱️ How much time does System.out.println() actually take? (You might be surprised) Most of us use System.out.println() everywhere — for debugging, logging, and quick checks. But have you ever asked: how expensive is it? 🧠 The short answer System.out.println() is slow compared to normal Java operations. ⏳ On average: 1–5 milliseconds per call (can be more) Depends on OS, console, and I/O buffering That may look small… until you put it inside a loop. ⚠️ Why is it slow? Because System.out.println(): 🔹 Writes to I/O stream (not memory) 🔹 Is synchronized (thread-safe → slower) 🔹 Flushes output to the console 🔹 Waits for the OS to handle the write This is thousands of times slower than in-memory operations. 🔁 Real impact for(int i = 0; i < 10000; i++) { System.out.println(i); } 👉 This can take seconds, not milliseconds. Now imagine this inside: REST APIs Microservices High-traffic applications 😬 ✅ What to do instead? ✔️ Use logging frameworks (Logback, Log4j2) ✔️ Log at proper levels (DEBUG, INFO) ✔️ Avoid console printing in production code 🏁 Final thought System.out.println() is great for learning and quick debugging, but in real applications — it can silently kill performance. 🔔 Follow for more insights on Java internals & backend performance 🚀 #Java #JavaDeveloper #CoreJava #AdvancedJava #JavaProgramming #Spring #SpringBoot #Hibernate #JPA #BackendDevelopment #Microservices #RESTAPI #SoftwareEngineering #CleanCode #TechLearning #CodingJourney #Programming

Spring Boot Annotation Cheat Sheet 📝 Stop memorizing and start understanding the "Magic" behind the framework. Here are the 10 essentials every Backend Developer should know: ⦿ @SpringBootApplication: The application entry point (Config + Auto-Config + Component Scan). ⦿ @Configuration: Marks a class as a source of bean definitions. ⦿ @PathVariable: Extracts values directly from the URI path. ⦿ @RequestBody: Maps the HttpRequest body to a transfer object (DTO). ⦿ @Autowired: Powers Dependency Injection Constructor injection is best!. ⦿ @RestController: Handles HTTP requests and returns JSON responses. ⦿ @Bean: Tells Spring that a method returns an object to be managed as a bean. ⦿ @EnableAutoConfiguration: Guesses and configures beans based on your classpath. ⦿ @Component: A generic stereotype for any Spring-managed component. ⦿ @Repository: Defines the Data Access layer and handles DB exceptions. The Drawback: Heavy use of annotations can lead to "Magic Fatigue." Behind every annotation is a Java proxy, understanding the why is just as important as the what. #Java #SpringBoot #BackendDevelopment #LearningInPublic #CleanCode #SoftwareEngineering

🚨 Your favourite collection might be your biggest bottleneck. We’ve all been there — we start out with ArrayList. It’s simple, fast, and works well for most cases. But as your application grows, that one-size-fits-all approach quietly becomes the reason for mysterious slowdowns. The Java Collections Framework (JCF) isn’t a buffet of similar options — it’s a power toolset designed for specific trade-offs. Knowing which one to pick can make your system faster and your code cleaner. Here’s a quick reality check 👇 ArrayList ➡️ Great for fast random access and cheap appends; but costly middle inserts or deletes. LinkedList ➡️ Best for frequent head/tail updates; but worse cache locality and higher memory cost. HashMap / HashSet ➡️ O(1) lookups; but no ordering, and hash collisions can bite you if keys aren’t well-designed. LinkedHashMap ➡️ Preserves insertion order — perfect for caches or predictable APIs. TreeMap / TreeSet ➡️ Keeps keys sorted; excellent when order matters more than speed. ⚙️ A few pro tips: Use ArrayList for “read-mostly” lists. If you’re iterating more than mutating, it’s your go-to. Avoid LinkedList unless you really need it. In most modern JVMs, it’s slower due to poor cache performance. Use EnumMap or EnumSet when keys are enums — highly memory and speed efficient. Initialize collection sizes upfront. Helps avoid resizing overhead, especially in tight loops. Prefer immutability — List.of() and Map.of() are your friends for static data. Choosing the right collection isn’t a micro-optimization — it’s a design decision that compounds as your system scales. So, what do you think? 👉 Which Java collection is overused or misused most in your experience? #Java #CollectionsFramework #DataStructures #Performance #SoftwareEngineering #CleanCode

📌 Spring Boot Annotation Series – Part 8 ✅ @Component annotation The @Component annotation is used to mark a class as a Spring-managed bean 👇 🔹 Why do we use @Component? To tell Spring: 👉 “Create an object of this class and manage it.” - To enable dependency injection - To let Spring detect the class during component scanning 🔹 How does it work? When Spring Boot starts: - It scans packages (using @ComponentScan) - Finds classes annotated with @Component - Creates and registers them as beans in the Spring container 🔹 Simple example @Component public class EmailService { public void sendEmail() { System.out.println("Email sent"); } } Now this class can be injected using: @Autowired private EmailService emailService; 🔹 In simple words @Component tells Spring to automatically create and manage this class as a bean. 👉 🧠 Quick Understanding - Marks a class as a Spring bean - Detected during component scanning - Enables dependency injection #SpringBoot #Java #Component #BackendDevelopment #LearningInPublic

I just published Part 7 of my Spring Boot series. This installment focuses on making your APIs professional and production-ready by effectively handling errors and validating requests. In this article, I cover: ✔️ Why exception handling matters ✔️ Custom exceptions (e.g., ResourceNotFoundException) ✔️ Global exception handling with @RestControllerAdvice ✔️ Request validation using @Valid, @NotBlank, @Email ✔️ Returning clean 400/404 JSON responses instead of messy errors Read here. #SpringBoot #Java #RESTAPI #BackendDevelopment #LearningInPublic

🚀 Day 13/100 - Spring Boot Annotations - 4️⃣ @Configuration & @Bean ➡️ @Configuration 🔹What is it - A class-level annotation which tells Spring that this class contains bean definitions for the IoC container. - It is a modern replacement for XML-based configuration. 🔹Why to use - Makes configuration type-safe - Easy to read and maintain - Fully Java-based (no XML) ➡️ @Bean 🔹What is it - A method-level annotation used inside a @Configuration class to explicitly create and register a bean in the Spring container. 🔹Why to use - Useful when you cannot modify a class (e.g., third-party libraries) - Gives full control over object creation and configuration 📌 Key Takeaway @Configuration → where beans are defined @Bean → how a bean is created Next post: https://lnkd.in/d3pztG-x Previous post: https://lnkd.in/d8NzCVkB #100Days #SpringBoot #Java #BackendDevelopment #SoftwareEngineering

🚦 Spring Boot Simplified: @Primary vs. @Qualifier 🚦 Ever found yourself with multiple beans of the same type in your Spring application and wondered how Spring knows which one to inject? 🤔 🌟 @Primary Think of this as setting a default. If multiple beans of a type exist, the one marked with @Primary is the one Spring picks—unless told otherwise. @Bean @Primary public DataSource primaryDataSource() { // ... } ✨ @Qualifier Want to be more explicit? Use @Qualifier to specify exactly which bean you want, by name! @Autowired @Qualifier("secondaryDataSource") private DataSource dataSource; 🔑 Key Takeaway: Use @Primary for a sensible default. Use @Qualifier for precision control. These annotations give you the flexibility to manage complex dependency graphs cleanly and clearly—making your codebase more robust and readable! #SpringBoot #Java #CodingTips #BeanInjection #SoftwareEngineering #SpringFramework

The moment Java systems begin handling snapshots, events, concurrent state, or domain aggregates, object copying stops being trivial. This is where the Copy Constructor approach becomes essential. A copy constructor gives developers: 🔹 full control over what gets duplicated 🔹 guaranteed avoidance of Cloneable's broken contract 🔹 clear semantics for nested objects 🔹 deterministic behavior under concurrency 🔹 predictable memory and lifecycle boundaries clone() suffers from reflection, shallow copying traps, CloneNotSupportedException, and inheritance fragility. Copy constructors avoid all of this by tying copying logic directly to the domain — not to a runtime mechanism. The result is a design where every replicated object is intentional, safe, and structurally consistent. This is exactly what high-integrity systems — financial flows, rule engines, schedulers, auditing pipelines — depend on. When correctness matters, explicit copying wins. Hashtags: #Java #CopyConstructor #AdvancedJava #JavaInternals #BackendEngineering #CleanArchitecture #ObjectOrientedDesign #CodeQuality #SoftwareEngineering #ConcurrencyControl #Immutability #ProgrammingBestPractices #DeepWork #JavaCommunity #HighPerformanceJava #TechLearning

🌱 My Spring Journey : Dependency Lookup -> Here, the target class writes the logic to obtain the dependent class object, and for this it uses the getBean(..) method. -> If the dependent class object is required in multiple methods of the target class, we should prefer Dependency Injection; otherwise, we can go for Dependency Lookup. Limitations of Dependency Lookup : -> For this approach, we need to create or access an extra IOC container inside the business method of the target class. -> Due to this, even singleton-scoped Spring beans may get pre-instantiated multiple times (when multiple containers are created). -> This extra IOC container creation process generates in-memory metadata for the Spring bean configuration files, which can lead to memory issues. -> To overcome this problem we can use Interface injection #SpringFramework #DependencyLookup #DependencyInjection #Java #SpringCore #BackendDevelopment #LearningJourney