Java code explainers

java

@Component
@Converter
public class EncryptedStringConverter implements AttributeConverter<String, String> {

Transparent column encryption in Spring & JPA

encryption aes-gcm jpa-converter

Advanced 10 steps

java

package com.acme.billing.config;
 
import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
import org.springframework.boot.context.properties.ConfigurationProperties;

Feature-flagged beans with Spring @ConditionalOnProperty

feature-flags conditional-beans strategy-pattern

Intermediate 5 steps

java

public static Map<String, String> parseCookieHeader(String header) {
    Map<String, String> cookies = new LinkedHashMap<>();
    if (header == null || header.isBlank()) {
        return cookies;

Parsing an HTTP Cookie header in Java

string-parsing http url-decoding

Intermediate 6 steps

java

public class TimedSocketReader {
 
    private static final int READ_TIMEOUT_MS = 5_000;
    private static final int CONNECT_TIMEOUT_MS = 3_000;

Reading a socket with connect and read timeouts

sockets timeouts io

Intermediate 8 steps

java

public final class EncodingDetector {
 
    public enum Encoding {
        UTF_8, UTF_16LE, UTF_16BE, UTF_32LE, UTF_32BE, ASCII, UNKNOWN

Detecting text encoding from raw bytes in Java

byte-manipulation encoding-detection bitwise-operations

Intermediate 8 steps

java

public final class ImportOrganizer {
 
    private static final Pattern IMPORT_LINE =
            Pattern.compile("^import\\s+(static\\s+)?([\\w.]+(?:\\.\\*)?)\\s*;\\s*$");

Sorting Java imports with a regex pass

regex sorting text-processing

Intermediate 8 steps

java

package com.example.api.config;
 
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;

Configuring CORS in Spring MVC

cors configuration dependency-injection

Intermediate 6 steps

java

@Configuration
public class PaymentGatewayClientConfig {
 
    @Bean

Building a resilient RestClient in Spring

retry http-client backoff

Intermediate 9 steps

java

public final class RetryExecutor {
 
    private final int maxAttempts;
    private final Duration baseDelay;

Retry with exponential backoff in Java

retry exponential-backoff jitter

Intermediate 7 steps

java

@Service
public class ProductLookupService {
 
    private final ProductRepository productRepository;

How Spring caching layers a product lookup

caching cache-eviction fallback

Intermediate 8 steps

java

public final class ThrottledLogger {
 
    private final Logger delegate;
    private final long windowMillis;

Rate-limiting log spam with per-message windows

concurrency rate-limiting throttling

Advanced 8 steps

java

public final class MapFlattener {
 
    private MapFlattener() {
    }

Flattening nested maps into dotted keys

recursion tree-traversal data-transformation

Intermediate 7 steps

java

package com.example.actuator;
 
import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.actuate.endpoint.annotation.Endpoint;

Building a custom Spring Boot Actuator endpoint

actuator dependency-injection observability

Intermediate 7 steps

java

@Configuration
public class ValidationConfig implements WebMvcConfigurer {
 
    @Bean

Localized bean validation messages in Spring

internationalization bean-validation configuration

Intermediate 6 steps

java

public final class ChunkSorter {
 
    private static final int MAX_LINES_PER_CHUNK = 100_000;

External merge sort in Java

external-sort merge-sort priority-queue

Advanced 10 steps

java

public record TimeSlot(LocalDate day, LocalDateTime start, LocalDateTime end) {}
 
public class ScheduleAnalyzer {

Detecting calendar conflicts in Java

streams sorting sweep-line

Intermediate 8 steps

java

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

Building a Spring MVC form controller

mvc form-handling validation

Intermediate 8 steps

java

public final class PrefixSearch {
 
    private final String[] words;

Prefix search with binary search bounds

binary-search sorting range-query

Intermediate 9 steps