Spring Boot ile RESTful API Geliştirme

Spring Boot, Java ekosisteminde en popüler framework’lerden biri. Minimal konfigürasyon ile production-ready uygulamalar geliştirmenizi sağlıyor. Bu yazıda temel bir REST API nasıl oluşturulur, adım adım göreceğiz.

Proje Kurulumu

Spring Initializr kullanarak yeni bir proje oluşturalım. Gerekli bağımlılıklar:

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-jpa</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-validation</artifactId>
    </dependency>
    <dependency>
        <groupId>com.h2database</groupId>
        <artifactId>h2</artifactId>
        <scope>runtime</scope>
    </dependency>
    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <optional>true</optional>
    </dependency>
</dependencies>

Entity Tanımlama

Önce bir Article entity’si oluşturalım:

package com.example.blog.entity;

import jakarta.persistence.*;
import jakarta.validation.constraints.NotBlank;
import jakarta.validation.constraints.Size;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.AllArgsConstructor;
import java.time.LocalDateTime;

@Entity
@Table(name = "articles")
@Data
@NoArgsConstructor
@AllArgsConstructor
public class Article {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @NotBlank(message = "Başlık boş olamaz")
    @Size(min = 3, max = 200)
    private String title;

    @NotBlank(message = "İçerik boş olamaz")
    @Column(columnDefinition = "TEXT")
    private String content;

    @Column(name = "created_at")
    private LocalDateTime createdAt;

    @Column(name = "updated_at")
    private LocalDateTime updatedAt;

    @PrePersist
    protected void onCreate() {
        createdAt = LocalDateTime.now();
        updatedAt = LocalDateTime.now();
    }

    @PreUpdate
    protected void onUpdate() {
        updatedAt = LocalDateTime.now();
    }
}

Repository Katmanı

Spring Data JPA ile repository oluşturmak çok basit:

package com.example.blog.repository;

import com.example.blog.entity.Article;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import org.springframework.stereotype.Repository;
import java.util.List;

@Repository
public interface ArticleRepository extends JpaRepository<Article, Long> {

    // Başlığa göre arama
    List<Article> findByTitleContainingIgnoreCase(String title);

    // En son eklenen makaleler
    List<Article> findTop10ByOrderByCreatedAtDesc();

    // Özel sorgu
    @Query("SELECT a FROM Article a WHERE a.content LIKE %:keyword%")
    List<Article> searchByContent(String keyword);
}

Service Katmanı

İş mantığını service katmanında tutuyoruz:

package com.example.blog.service;

import com.example.blog.entity.Article;
import com.example.blog.repository.ArticleRepository;
import com.example.blog.exception.ResourceNotFoundException;
import lombok.RequiredArgsConstructor;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;
import java.util.List;

@Service
@RequiredArgsConstructor
public class ArticleService {

    private final ArticleRepository articleRepository;

    public List<Article> getAllArticles() {
        return articleRepository.findAll();
    }

    public Article getArticleById(Long id) {
        return articleRepository.findById(id)
            .orElseThrow(() -> new ResourceNotFoundException("Makale bulunamadı: " + id));
    }

    @Transactional
    public Article createArticle(Article article) {
        return articleRepository.save(article);
    }

    @Transactional
    public Article updateArticle(Long id, Article articleDetails) {
        Article article = getArticleById(id);
        article.setTitle(articleDetails.getTitle());
        article.setContent(articleDetails.getContent());
        return articleRepository.save(article);
    }

    @Transactional
    public void deleteArticle(Long id) {
        Article article = getArticleById(id);
        articleRepository.delete(article);
    }

    public List<Article> searchArticles(String query) {
        return articleRepository.findByTitleContainingIgnoreCase(query);
    }
}

REST Controller

Son olarak API endpoint’lerini tanımlayalım:

package com.example.blog.controller;

import com.example.blog.entity.Article;
import com.example.blog.service.ArticleService;
import jakarta.validation.Valid;
import lombok.RequiredArgsConstructor;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.*;
import java.util.List;

@RestController
@RequestMapping("/api/articles")
@RequiredArgsConstructor
public class ArticleController {

    private final ArticleService articleService;

    @GetMapping
    public ResponseEntity<List<Article>> getAllArticles() {
        return ResponseEntity.ok(articleService.getAllArticles());
    }

    @GetMapping("/{id}")
    public ResponseEntity<Article> getArticleById(@PathVariable Long id) {
        return ResponseEntity.ok(articleService.getArticleById(id));
    }

    @PostMapping
    public ResponseEntity<Article> createArticle(@Valid @RequestBody Article article) {
        Article created = articleService.createArticle(article);
        return ResponseEntity.status(HttpStatus.CREATED).body(created);
    }

    @PutMapping("/{id}")
    public ResponseEntity<Article> updateArticle(
            @PathVariable Long id,
            @Valid @RequestBody Article article) {
        return ResponseEntity.ok(articleService.updateArticle(id, article));
    }

    @DeleteMapping("/{id}")
    public ResponseEntity<Void> deleteArticle(@PathVariable Long id) {
        articleService.deleteArticle(id);
        return ResponseEntity.noContent().build();
    }

    @GetMapping("/search")
    public ResponseEntity<List<Article>> searchArticles(@RequestParam String q) {
        return ResponseEntity.ok(articleService.searchArticles(q));
    }
}

Global Exception Handler

Hataları merkezi bir yerde yönetmek için:

package com.example.blog.exception;

import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.MethodArgumentNotValidException;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.RestControllerAdvice;
import java.time.LocalDateTime;
import java.util.HashMap;
import java.util.Map;

@RestControllerAdvice
public class GlobalExceptionHandler {

    @ExceptionHandler(ResourceNotFoundException.class)
    public ResponseEntity<Map<String, Object>> handleResourceNotFound(
            ResourceNotFoundException ex) {
        Map<String, Object> error = new HashMap<>();
        error.put("timestamp", LocalDateTime.now());
        error.put("message", ex.getMessage());
        error.put("status", HttpStatus.NOT_FOUND.value());
        return ResponseEntity.status(HttpStatus.NOT_FOUND).body(error);
    }

    @ExceptionHandler(MethodArgumentNotValidException.class)
    public ResponseEntity<Map<String, Object>> handleValidationErrors(
            MethodArgumentNotValidException ex) {
        Map<String, Object> error = new HashMap<>();
        Map<String, String> fieldErrors = new HashMap<>();

        ex.getBindingResult().getFieldErrors().forEach(fieldError ->
            fieldErrors.put(fieldError.getField(), fieldError.getDefaultMessage())
        );

        error.put("timestamp", LocalDateTime.now());
        error.put("errors", fieldErrors);
        error.put("status", HttpStatus.BAD_REQUEST.value());
        return ResponseEntity.badRequest().body(error);
    }
}

Sonuç

Spring Boot ile temiz, katmanlı bir REST API oluşturmak oldukça kolay. Bu yapı sayesinde:

Bakımı kolay kod yazabilirsiniz
Test edilebilir bir mimari elde edersiniz
Ölçeklenebilir uygulamalar geliştirebilirsiniz

Bir sonraki yazıda Spring Security ile JWT authentication eklemeyi göreceğiz.