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Creating RESTful Services in Java

This guide walks through building a complete REST API with Spring Boot — from project setup to handling requests, validation, and structured error responses.

Project Setup

Use Spring Initializr (start.spring.io) with Spring Web dependency. JDK 17+, Maven or Gradle. The embedded Tomcat server runs your API on port 8080.

Controller Layer

@RestController
@RequestMapping("/api/v1/books")
@RequiredArgsConstructor
public class BookController {
    private final BookService bookService;

    @GetMapping
    public List<BookDto> list(@RequestParam(defaultValue = "0") int page) {
        return bookService.findAll(page);
    }

    @PostMapping
    public ResponseEntity<BookDto> create(@Valid @RequestBody CreateBookRequest req) {
        BookDto created = bookService.create(req);
        return ResponseEntity.status(HttpStatus.CREATED).body(created);
    }
}

Layered Architecture

  • Controller — HTTP layer, request/response mapping.
  • Service — Business logic, transactions.
  • Repository — Data access (JPA, JDBC).
  • DTO — Data transfer objects for API contracts.
  • Entity — Database-mapped objects (keep separate from DTOs).

Frequently Asked Questions

Should I expose JPA entities directly?▼

No. Use DTOs to control the API contract, hide internal fields, and prevent lazy-loading serialization issues.

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