Building a REST API with Spring Boot

Building a REST API with Spring Boot

Spring Boot makes building REST APIs remarkably fast. With a few annotations you can have a fully functional API with JSON serialization, validation, and error handling.

Project Setup

Start with the Spring Initializr. Select Spring Web and Spring Data JPA. Spring Boot auto-configures Jackson for JSON conversion, an embedded Tomcat, and much more.

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>

The Model

@Entity
@Table(name = "products")
public class Product {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private double price;
    private String category;

    // getters and setters
}

The Controller

The @RestController annotation combines @Controller and @ResponseBody. Every method return value is serialized to JSON automatically.

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

    @Autowired
    private ProductService productService;

    @GetMapping
    public List<Product> getAll() {
        return productService.findAll();
    }

    @GetMapping("/{id}")
    public Product getById(@PathVariable Long id) {
        return productService.findById(id)
            .orElseThrow(() -> new ResourceNotFoundException("Product not found"));
    }

    @PostMapping
    @ResponseStatus(HttpStatus.CREATED)
    public Product create(@Valid @RequestBody Product product) {
        return productService.save(product);
    }

    @PutMapping("/{id}")
    public Product update(@PathVariable Long id, @Valid @RequestBody Product product) {
        return productService.update(id, product);
    }

    @DeleteMapping("/{id}")
    @ResponseStatus(HttpStatus.NO_CONTENT)
    public void delete(@PathVariable Long id) {
        productService.delete(id);
    }
}

Auto-Configuration Magic

Spring Boot detects Jackson on the classpath and automatically configures message converters. Return a Java object from a controller method and it becomes JSON in the response. Send JSON in the request body with @RequestBody and Spring parses it into a Java object.

Running It

Run the main class. The API is live at http://localhost:8080/api/products. No XML configuration. No deployment descriptor. Just annotations and code.

Key Points

• @RestController makes every method return JSON automatically.
• @GetMapping, @PostMapping, @PutMapping, @DeleteMapping map HTTP methods.
• @RequestBody deserializes JSON input; return values serialize to JSON.
• Spring Boot auto-configures Jackson, Tomcat, and message converters.
• Use @Valid with Bean Validation for automatic input validation.