Java code explainers

java

package com.example.web.convert;
 
import java.time.LocalDate;
import java.time.format.DateTimeFormatter;

A custom ISO-week Converter in Spring

type conversion value object immutability

Intermediate 5 steps

java

import java.io.IOException;
import java.io.InputStream;
import java.net.URI;
import java.net.http.HttpClient;

Streaming a file download with Java's HttpClient

http-client streaming file-io

Intermediate 6 steps

java

@RestController
@RequestMapping("/api/documents")
@RequiredArgsConstructor
public class DocumentController {

Method-level authorization with @PreAuthorize in Spring

authorization spel rest-api

Intermediate 7 steps

java

@WebMvcTest(OrderController.class)
class OrderControllerTest {
 
    @Autowired

Slicing the web layer with @WebMvcTest in Spring

testing mocking web-layer

Intermediate 9 steps

java

@Repository
public interface OrderRepository extends JpaRepository<Order, Long> {
 
    @EntityGraph(attributePaths = {"customer", "lineItems", "lineItems.product"})

Killing N+1 queries with @EntityGraph in Spring

orm fetching n+1-problem

Intermediate 5 steps

java

@RestController
@RequestMapping("/api/orders")
public class OrderController {

Content-negotiated API versioning in Spring

api-versioning content-negotiation rest

Intermediate 7 steps

java

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

Resilient payment calls in Spring

circuit breaker retry fault tolerance

Intermediate 7 steps

java

@Target(ElementType.PARAMETER)
@Retention(RetentionPolicy.RUNTIME)
public @interface CurrentUser {
}

Injecting the current user in Spring MVC

annotations dependency-injection security

Intermediate 8 steps

java

public final class TokenBucketRateLimiter {
 
    private final long capacity;
    private final double refillTokensPerNano;

How a token bucket rate limiter works

rate-limiting concurrency token-bucket

Intermediate 8 steps

java

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

Binding paged search filters in Spring

data-binding validation pagination

Intermediate 7 steps

java

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

Testing a JPA repository against real Postgres in Spring

integration-testing testcontainers jpa

Intermediate 8 steps

java

@Aspect
@Component
public class IdempotencyAspect {

How an idempotency aspect works in Spring

aop idempotency caching

Advanced 9 steps

java

public final class ListPartitioner {
 
    private ListPartitioner() {
    }

Splitting a list into fixed-size chunks in Java

generics partitioning streams

Intermediate 8 steps

java

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

Manual RabbitMQ acks in a Spring listener

message-queue error-handling acknowledgement

Intermediate 6 steps

java

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

Deriving JPA queries from method names in Spring

query derivation repositories pagination

Intermediate 8 steps

java

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

Aggregating stats with IntSummaryStatistics

streams aggregation records

Intermediate 5 steps

java

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

Batched JDBC inserts with transaction safety

jdbc batching transactions

Intermediate 8 steps

java

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

Centralized error handling in Spring

exception-handling problemdetail rest-api

Intermediate 7 steps