Spring Boot In Action ((hot)) May 2026

@Service public class UserService { @Cacheable(value = "users", key = "#id") public User findById(Long id) { return userRepository.findById(id).orElseThrow(); }

public interface UserRepository extends JpaRepository<User, Long> { Optional<User> findByEmail(String email); @Query("SELECT u FROM User u WHERE u.email LIKE %:domain") List<User> findByEmailDomain(@Param("domain") String domain); } @Repository public class JdbcUserRepository { private final JdbcTemplate jdbcTemplate; public List<User> findAll() { return jdbcTemplate.query("SELECT * FROM users", (rs, rowNum) -> new User(rs.getLong("id"), rs.getString("email"))); } } MongoDB, Redis, etc. // MongoDB @Document(collection = "products") public class Product { } // Redis @RedisHash("sessions") public class UserSession { } 4. Web Development REST Controllers @RestController @RequestMapping("/api/users") public class UserController { @GetMapping public ResponseEntity<List<User>> getAll() { return ResponseEntity.ok(users); }

@Scheduled(initialDelay = 10000, fixedRate = 30000) public void fixedRateTask() { } } @Configuration @EnableAsync public class AsyncConfig implements AsyncConfigurer { @Override public Executor getAsyncExecutor() { ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor(); executor.setCorePoolSize(5); executor.setMaxPoolSize(10); executor.setQueueCapacity(100); executor.initialize(); return executor; } } spring boot in action

@Scheduled(fixedDelay = 5000) public void fixedDelayTask() { // Runs 5 seconds after previous execution }

@Component @RabbitListener(queues = "order.queue") public class OrderListener { @RabbitHandler public void handleOrder(Order order) { System.out.println("Received order: " + order.getId()); } } File Upload @PostMapping("/upload") public ResponseEntity<String> handleUpload(@RequestParam("file") MultipartFile file) throws IOException { Path path = Paths.get("uploads/" + file.getOriginalFilename()); Files.write(path, file.getBytes()); return ResponseEntity.ok("File uploaded successfully"); } // Async file processing @Async public CompletableFuture<String> processFile(MultipartFile file) { // Process large files asynchronously } 14. Error Handling Global Exception Handler @RestControllerAdvice public class GlobalExceptionHandler { @ExceptionHandler(MethodArgumentNotValidException.class) @ResponseStatus(HttpStatus.BAD_REQUEST) public Map<String, String> handleValidation(MethodArgumentNotValidException ex) { return ex.getBindingResult().getFieldErrors().stream() .collect(Collectors.toMap( FieldError::getField, FieldError::getDefaultMessage )); } Health

This comprehensive guide covers the essential features of Spring Boot in action for building production-ready applications.

@Bean public PasswordEncoder passwordEncoder() { return new BCryptPasswordEncoder(); } } @Service public class JwtService { public String generateToken(User user) { return Jwts.builder() .setSubject(user.getEmail()) .claim("roles", user.getRoles()) .setIssuedAt(new Date()) .setExpiration(new Date(System.currentTimeMillis() + 86400000)) .signWith(getSigningKey(), SignatureAlgorithm.HS256) .compact(); } } 6. Actuator & Monitoring Enable Actuator management: endpoints: web: exposure: include: health,info,metrics,prometheus endpoint: health: show-details: always metrics: export: prometheus: enabled: true Custom Health Indicator @Component public class CustomHealthIndicator implements HealthIndicator { @Override public Health health() { boolean healthy = checkExternalService(); return healthy ? Health.up().build() : Health.down().withDetail("reason", "Service unavailable").build(); } } Custom Metrics @Service public class MonitoredService { private final Counter requestCounter; public MonitoredService(MeterRegistry meterRegistry) { this.requestCounter = Counter.builder("api.requests.total") .description("Total API requests") .register(meterRegistry); } Health.up().build() : Health.down().withDetail("reason"

@GetMapping("/{id}") public ResponseEntity<User> getById(@PathVariable Long id) { return userService.findById(id) .map(ResponseEntity::ok) .orElse(ResponseEntity.notFound().build()); }