Java code explainers

java

@Configuration
@EnableRedisHttpSession(namespace = "myapp:sessions", maxInactiveIntervalInSeconds = 1800, flushMode = FlushMode.IMMEDIATE)
public class SessionConfig {

Backing HTTP sessions with Redis in Spring

session-management redis distributed-state

Intermediate 7 steps

java

public List<User> findUsersByEmailDomain(String domain, int minAge) {
    String sql = """
        SELECT id, username, email, age, created_at
        FROM users

Safe parameterized JDBC queries in Java

jdbc sql-injection prepared-statement

Intermediate 7 steps

java

@Configuration
@EnableBatchProcessing
public class CustomerImportJobConfig {

How a chunk-based CSV import job works in Spring

batch-processing etl csv-parsing

Intermediate 9 steps

java

@Configuration
@EnableWebSecurity
public class ResourceServerConfig {

Configuring a JWT resource server in Spring

oauth2 jwt authorization

Intermediate 8 steps

java

@Configuration
public class OrderConsumerConfig {
 
    @Bean

Wiring a resilient Kafka consumer in Spring

kafka deserialization error-handling

Intermediate 8 steps

java

@Configuration
@EnableKafka
public class KafkaErrorHandlingConfig {

Kafka retry and dead-letter handling in Spring

kafka error-handling retry

Intermediate 7 steps

java

@Controller
@RequestMapping("/employees")
public class EmployeeController {

Customizing form binding in a Spring MVC controller

data-binding validation type-conversion

Intermediate 9 steps

java

package com.example.config.condition;
 
import org.springframework.context.annotation.Condition;
import org.springframework.context.annotation.ConditionContext;

A custom @Conditional feature flag in Spring

conditional beans feature flags annotations

Intermediate 7 steps

java

public List<OrderSummary> streamRecentOrders(LocalDateTime since, Consumer<OrderSummary> handler) {
    String sql = """
        SELECT id, customer_id, total_cents, status, created_at
        FROM orders

Streaming large JDBC result sets safely

jdbc streaming resource-management

Intermediate 7 steps

java

public class DuplicateFinder {
 
    public Map<String, List<Path>> findDuplicates(Path root) throws IOException {
        Map<String, List<Path>> byHash = new HashMap<>();

Finding duplicate files by content hash

hashing file-io streams

Intermediate 8 steps

java

@Component
public class OrderRecoveryHandler {
 
    private final RabbitTemplate rabbitTemplate;

Dead-letter recovery with Spring AMQP

dead-letter-queue retry exponential-backoff

Advanced 9 steps

java

@Component
public class CorrelationIdWebFilter implements WebFilter, Ordered {
 
    public static final String CORRELATION_ID_HEADER = "X-Correlation-Id";

Correlation IDs in a Spring WebFlux filter

reactive web filter correlation id

Advanced 7 steps

java

public final class DeepCopier {
 
    private static final ObjectMapper MAPPER = new ObjectMapper()
            .registerModule(new JavaTimeModule())

Deep-copying objects via Jackson serialization

serialization deep-copy generics

Intermediate 7 steps

java

package com.example.time;
 
import java.time.Duration;
import java.time.Instant;

Adding ISO-8601 durations across time zones in Java

date-time iso-8601 parsing

Intermediate 7 steps

java

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

Distributed scheduled jobs with Spring locks

distributed-locking scheduling concurrency

Advanced 8 steps

java

import java.util.Comparator;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.regex.Pattern;

Ranking the most frequent words in Java

streams regex grouping

Intermediate 7 steps

java

public final class HttpHeaders {
 
    private final NavigableMap<String, List<String>> values =
            new TreeMap<>(String.CASE_INSENSITIVE_ORDER);

A case-insensitive HTTP headers map in Java

case-insensitivity multimap immutability

Intermediate 7 steps

java

public record ServerConfig(
        String host,
        int port,
        Duration timeout,

Loading typed config into a Java record

records factory-methods parsing

Intermediate 7 steps