Controller Layer (@RestController)

Controller Responsibilities

The Controller Layer is the entry point for HTTP requests into your web application. It handles request validation, status code assignment, and JSON serialization.

@RestController vs @Controller:

• @Controller: Used in traditional web apps returning HTML templates (Thymeleaf/JSP). Requires @ResponseBody on methods.
• @RestController: Combination of @Controller + @ResponseBody. Automatically serializes returned Java objects into JSON/XML payloads.

Production Code Example:

package com.anujsingh.digitalguru.controller;

import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.*;
import com.anujsingh.digitalguru.model.Product;

@RestController
@RequestMapping("/api/products")
public class ProductController {

    @GetMapping("/{id}")
    public ResponseEntity<Product> getProduct(@PathVariable Long id) {
        Product product = new Product(id, "Laptop", 1200.00);
        return ResponseEntity.ok(product);
    }
}

Key Architectural Concepts & Best Practices:

When working with Controller Layer (@RestController) in enterprise Spring Boot applications, keep these key architectural guidelines in mind:

• Separation of Concerns: Maintain a strict boundary between HTTP endpoints, service logic, and database persistence layers.
• Framework Conventions: Rely on Spring Boot auto-configuration defaults whenever possible, overriding settings only via application.yml or @Configuration classes when customized behavior is required.
• Production Monitoring & Reliability: Ensure proper exception handling, thread-safety, and resource cleanup to prevent memory leaks and unexpected runtime downtime.
• Developer Ergonomics: Write clean, self-documenting code with modern Java features (Records, Lambdas, Streams) to simplify code reviews and maintenance.

Summary Takeaway:

Mastering Controller Layer (@RestController) ensures that your Java & Spring Boot backend microservices remain maintainable, secure, and compliant with modern enterprise software engineering standards.