Spring Boot Application

Overview

Develop production-ready Spring Boot applications with proper annotation-based configuration, dependency injection, REST controllers, JPA data persistence, service layers, and security implementation following Spring conventions.

When to Use

• Building Spring Boot REST APIs
• Implementing service-oriented architectures
• Configuring data persistence with JPA
• Managing dependency injection
• Implementing Spring Security
• Building microservices with Spring Boot

Instructions

1. Spring Boot Project Setup

<!-- pom.xml -->
<project>
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.example</groupId>
    <artifactId>api-service</artifactId>
    <version>1.0.0</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>3.1.0</version>
    </parent>

    <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-security</artifactId>
        </dependency>
        <dependency>
            <groupId>org.postgresql</groupId>
            <artifactId>postgresql</artifactId>
        </dependency>
        <dependency>
            <groupId>io.jsonwebtoken</groupId>
            <artifactId>jjwt</artifactId>
            <version>0.12.3</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
</project>

2. Entity Models with JPA Annotations

// User.java
package com.example.model;

import jakarta.persistence.*;
import java.time.LocalDateTime;
import java.util.Collection;
import org.springframework.security.core.GrantedAuthority;
import org.springframework.security.core.authority.SimpleGrantedAuthority;
import org.springframework.security.core.userdetails.UserDetails;

@Entity
@Table(name = "users", indexes = {
    @Index(name = "idx_email", columnList = "email", unique = true),
    @Index(name = "idx_role", columnList = "role")
})
public class User implements UserDetails {
    @Id
    @GeneratedValue(strategy = GenerationType.UUID)
    private String id;

    @Column(unique = true, nullable = false)
    private String email;

    @Column(nullable = false)
    private String passwordHash;

    @Column(name = "first_name")
    private String firstName;

    @Column(name = "last_name")
    private String lastName;

    @Enumerated(EnumType.STRING)
    @Column(nullable = false)
    private Role role = Role.USER;

    @Column(name = "is_active")
    private Boolean isActive = true;

    @Column(name = "created_at", nullable = false, updatable = false)
    private LocalDateTime createdAt = LocalDateTime.now();

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

    @OneToMany(mappedBy = "author", cascade = CascadeType.ALL, orphanRemoval = true)
    private Collection<Post> posts;

    // Getters and setters
    @Override
    public String getUsername() {
        return email;
    }

    @Override
    public String getPassword() {
        return passwordHash;
    }

    @Override
    public Collection<? extends GrantedAuthority> getAuthorities() {
        return java.util.List.of(new SimpleGrantedAuthority(role.name()));
    }

    @Override
    public boolean isEnabled() {
        return isActive;
    }

    public enum Role {
        USER, ADMIN
    }
}

// Post.java
@Entity
@Table(name = "posts")
public class Post {
    @Id
    @GeneratedValue(strategy = GenerationType.UUID)
    private String id;

    @Column(nullable = false)
    private String title;

    @Column(nullable = false, columnDefinition = "TEXT")
    private String content;

    @Column(nullable = false)
    private Boolean published = false;

    @ManyToOne(fetch = FetchType.LAZY, optional = false)
    @JoinColumn(name = "user_id")
    private User author;

    @Column(name = "created_at", nullable = false, updatable = false)
    private LocalDateTime createdAt = LocalDateTime.now();

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

    // Getters and setters
}

3. Repository Layer with Spring Data JPA

// UserRepository.java
package com.example.repository;

import com.example.model.User;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.Pageable;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import org.springframework.stereotype.Repository;
import java.util.Optional;

@Repository
public interface UserRepository extends JpaRepository<User, String> {
    Optional<User> findByEmail(String email);

    @Query("SELECT u FROM User u WHERE u.email LIKE %:search% OR u.firstName LIKE %:search%")
    Page<User> searchUsers(String search, Pageable pageable);

    Page<User> findByRole(User.Role role, Pageable pageable);
}

// PostRepository.java
@Repository
public interface PostRepository extends JpaRepository<Post, String> {
    Page<Post> findByAuthorAndPublishedTrue(User author, Pageable pageable);

    @Query(value = "SELECT p FROM Post p WHERE p.published = true ORDER BY p.createdAt DESC",
           countQuery = "SELECT COUNT(p) FROM Post p WHERE p.published = true")
    Page<Post> findPublishedPosts(Pageable pageable);

    Long countByAuthorId(String authorId);
}

4. Service Layer with Business Logic

// UserService.java
package com.example.service;

import com.example.model.User;
import com.example.repository.UserRepository;
import lombok.RequiredArgsConstructor;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.Pageable;
import org.springframework.security.crypto.password.PasswordEncoder;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;
import java.util.Optional;

@Service
@RequiredArgsConstructor
@Transactional
public class UserService {
    private final UserRepository userRepository;
    private final PasswordEncoder passwordEncoder;

    public User createUser(String email, String password, String firstName, String lastName) {
        if (userRepository.findByEmail(email).isPresent()) {
            throw new IllegalArgumentException("Email already exists");
        }

        User user = new User();
        user.setEmail(email);
        user.setPasswordHash(passwordEncoder.encode(password));
        user.setFirstName(firstName);
        user.setLastName(lastName);

        return userRepository.save(user);
    }

    @Transactional(readOnly = true)
    public Page<User> getUsers(String search, Pageable pageable) {
        if (search != null && !search.isBlank()) {
            return userRepository.searchUsers(search, pageable);
        }
        return userRepository.findAll(pageable);
    }

    @Transactional(readOnly = true)
    public Optional<User> getUserById(String id) {
        return userRepository.findById(id);
    }

    public User updateUser(String id, String firstName, String lastName) {
        User user = userRepository.findById(id)
            .orElseThrow(() -> new IllegalArgumentException("User not found"));

        if (firstName != null) user.setFirstName(firstName);
        if (lastName != null) user.setLastName(lastName);

        return userRepository.save(user);
    }

    public void deleteUser(String id) {
        userRepository.deleteById(id);
    }
}

// PostService.java
@Service
@RequiredArgsConstructor
@Transactional
public class PostService {
    private final PostRepository postRepository;
    private final UserRepository userRepository;

    public Post createPost(String userId, String title, String content) {
        User author = userRepository.findById(userId)
            .orElseThrow(() -> new IllegalArgumentException("User not found"));

        Post post = new Post();
        post.setTitle(title);
        post.setContent(content);
        post.setAuthor(author);

        return postRepository.save(post);
    }

    @Transactional(readOnly = true)
    public Page<Post> getPublishedPosts(Pageable pageable) {
        return postRepository.findPublishedPosts(pageable);
    }

    public Post publishPost(String postId) {
        Post post = postRepository.findById(postId)
            .orElseThrow(() -> new IllegalArgumentException("Post not found"));
        post.setPublished(true);
        return postRepository.save(post);
    }
}

5. REST Controllers with Request/Response Handling

// UserController.java
package com.example.controller;

import com.example.model.User;
import com.example.service.UserService;
import lombok.RequiredArgsConstructor;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.Pageable;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.security.access.prepost.PreAuthorize;
import org.springframework.web.bind.annotation.*;

@RestController
@RequestMapping("/api/users")
@RequiredArgsConstructor
public class UserController {
    private final UserService userService;

    @GetMapping
    public ResponseEntity<Page<User>> getUsers(
            @RequestParam(required = false) String search,
            Pageable pageable) {
        Page<User> users = userService.getUsers(search, pageable);
        return ResponseEntity.ok(users);
    }

    @GetMapping("/{id}")
    public ResponseEntity<User> getUser(@PathVariable String id) {
        return userService.getUserById(id)
            .map(ResponseEntity::ok)
            .orElseGet(() -> ResponseEntity.notFound().build());
    }

    @PostMapping
    public ResponseEntity<User> createUser(@RequestBody CreateUserRequest request) {
        User user = userService.createUser(
            request.getEmail(),
            request.getPassword(),
            request.getFirstName(),
            request.getLastName()
        );
        return ResponseEntity.status(HttpStatus.CREATED).body(user);
    }

    @PatchMapping("/{id}")
    @PreAuthorize("@securityService.isCurrentUser(#id)")
    public ResponseEntity<User> updateUser(
            @PathVariable String id,
            @RequestBody UpdateUserRequest request) {
        User user = userService.updateUser(id, request.getFirstName(), request.getLastName());
        return ResponseEntity.ok(user);
    }

    @DeleteMapping("/{id}")
    @PreAuthorize("hasRole('ADMIN')")
    public ResponseEntity<Void> deleteUser(@PathVariable String id) {
        userService.deleteUser(id);
        return ResponseEntity.noContent().build();
    }
}

// DTO classes
@Data
class CreateUserRequest {
    private String email;
    private String password;
    private String firstName;
    private String lastName;
}

@Data
class UpdateUserRequest {
    private String firstName;
    private String lastName;
}

6. Spring Security Configuration

// SecurityConfig.java
package com.example.config;

import com.example.security.JwtAuthenticationFilter;
import lombok.RequiredArgsConstructor;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.security.authentication.AuthenticationManager;
import org.springframework.security.config.annotation.authentication.builders.AuthenticationManagerBuilder;
import org.springframework.security.config.annotation.web.builders.HttpSecurity;
import org.springframework.security.config.annotation.web.configuration.EnableWebSecurity;
import org.springframework.security.config.http.SessionCreationPolicy;
import org.springframework.security.crypto.bcrypt.BCryptPasswordEncoder;
import org.springframework.security.crypto.password.PasswordEncoder;
import org.springframework.security.web.SecurityFilterChain;
import org.springframework.security.web.authentication.UsernamePasswordAuthenticationFilter;

@Configuration
@EnableWebSecurity
@RequiredArgsConstructor
public class SecurityConfig {
    private final JwtAuthenticationFilter jwtAuthenticationFilter;

    @Bean
    public PasswordEncoder passwordEncoder() {
        return new BCryptPasswordEncoder();
    }

    @Bean
    public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
        http
            .csrf().disable()
            .sessionManagement().sessionCreationPolicy(SessionCreationPolicy.STATELESS)
            .and()
            .authorizeHttpRequests()
            .requestMatchers("/api/auth/**").permitAll()
            .requestMatchers("/api/users/**").authenticated()
            .anyRequest().authenticated()
            .and()
            .addFilterBefore(jwtAuthenticationFilter, UsernamePasswordAuthenticationFilter.class);

        return http.build();
    }
}

// JwtAuthenticationFilter.java
@Component
@RequiredArgsConstructor
public class JwtAuthenticationFilter extends OncePerRequestFilter {
    private final JwtTokenProvider tokenProvider;
    private final UserDetailsService userDetailsService;

    @Override
    protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response,
                                    FilterChain filterChain) throws ServletException, IOException {
        try {
            String token = getJwtFromRequest(request);
            if (token != null && tokenProvider.validateToken(token)) {
                String userId = tokenProvider.getUserIdFromToken(token);
                UserDetails userDetails = userDetailsService.loadUserByUsername(userId);
                UsernamePasswordAuthenticationToken authentication =
                    new UsernamePasswordAuthenticationToken(userDetails, null, userDetails.getAuthorities());
                SecurityContextHolder.getContext().setAuthentication(authentication);
            }
        } catch (Exception ex) {
            logger.error("Could not set user authentication", ex);
        }

        filterChain.doFilter(request, response);
    }

    private String getJwtFromRequest(HttpServletRequest request) {
        String bearerToken = request.getHeader("Authorization");
        if (bearerToken != null && bearerToken.startsWith("Bearer ")) {
            return bearerToken.substring(7);
        }
        return null;
    }
}

7. Application Configuration

# application.yml
spring:
  application:
    name: api-service
  datasource:
    url: jdbc:postgresql://localhost:5432/mydb
    username: ${DB_USER}
    password: ${DB_PASSWORD}
    driver-class-name: org.postgresql.Driver
  jpa:
    hibernate:
      ddl-auto: validate
    properties:
      hibernate:
        dialect: org.hibernate.dialect.PostgreSQLDialect
  security:
    jwt:
      secret: ${JWT_SECRET}
      expiration: 86400000

server:
  port: 8080
  servlet:
    context-path: /

Best Practices

✅ DO

• Use dependency injection for loose coupling
• Implement service layer for business logic
• Use repositories for data access
• Leverage Spring Security for authentication
• Use @Transactional for transaction management
• Validate input in controllers
• Return appropriate HTTP status codes
• Use DTOs for request/response mapping
• Implement proper exception handling
• Use Spring’s @Async for async operations

❌ DON’T

• Put business logic in controllers
• Access database directly in controllers
• Store secrets in configuration files
• Use eager loading for large relationships
• Ignore transaction boundaries
• Return database entities in API responses
• Implement authentication in controllers
• Use raw SQL without parameterized queries
• Forget to validate user input

Complete Example

@SpringBootApplication
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}

@RestController
@RequestMapping("/api")
public class SimpleController {
    @GetMapping("/health")
    public ResponseEntity<String> health() {
        return ResponseEntity.ok("OK");
    }
}