Java code explainers

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

@DataJpaTest
@Testcontainers
@AutoConfigureTestDatabase(replace = AutoConfigureTestDatabase.Replace.NONE)
class OrderRepositoryIT {

@Aspect
@Component
public class IdempotencyAspect {
 

public final class ListPartitioner {
 
    private ListPartitioner() {
    }

package com.example.orders.messaging;
 
import com.example.orders.dto.OrderEvent;
import com.example.orders.service.OrderProcessingService;

package com.example.shop.repository;
 
import com.example.shop.domain.Order;
import com.example.shop.domain.OrderStatus;

import java.util.List;
import java.util.IntSummaryStatistics;
 
public class OrderReport {

public class OrderRepository {
 
    private static final int BATCH_SIZE = 500;
    private static final String INSERT_SQL =

@RestControllerAdvice
public class GlobalExceptionHandler {
 
    private static final Logger log = LoggerFactory.getLogger(GlobalExceptionHandler.class);

public List<String> collectTagsFromArticles(List<Article> articles) {
    return articles.stream()
        .flatMap(article -> article.getTags().stream())
        .map(String::trim)

@Component
@Order(20)
public class ProductSearchIndexRunner implements ApplicationRunner {
 

public final class FileChecksum {
 
    private static final char[] HEX = "0123456789abcdef".toCharArray();
 

@Service
public class OrderCheckoutService {
 
    private final OrderRepository orderRepository;

@Service
public class OrderMetricsService {
 
    private final MeterRegistry registry;

@RestController
@RequestMapping("/api/files")
public class FileUploadController {
 

package com.example.fs;
 
import java.io.IOException;
import java.nio.file.FileSystems;

public final class QueryParams {
 
    private final Map<String, List<String>> params;
 

public final class ShippingAddress {
    private final String recipient;
    private final String line1;
    private final String line2;