Java code explainers

java

public interface GitHubClient {
 
    @GetExchange("/users/{username}")
    GitHubUser getUser(@PathVariable String username);

Declarative HTTP clients in Spring

http-client declarative-api proxy

Intermediate 8 steps

java

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

Building a trie for autocomplete in Java

trie prefix-tree recursion

Intermediate 8 steps

java

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

Binding collection query params in Spring

rest-api query-parameters dependency-injection

Intermediate 6 steps

java

import java.util.ArrayDeque;
import java.util.Deque;
import java.util.Map;

Evaluating math expressions with two stacks

stacks parsing operator-precedence

Intermediate 9 steps

java

@Entity
@Table(name = "orders")
@SQLDelete(sql = "UPDATE orders SET deleted = true, deleted_at = now() WHERE id = ?")
@Where(clause = "deleted = false")

Soft deletes with Hibernate in Spring

soft-delete jpa hibernate

Intermediate 9 steps

java

@GetMapping("/files/{id}")
public ResponseEntity<StreamingResponseBody> download(
        @PathVariable String id,
        @RequestHeader(value = HttpHeaders.RANGE, required = false) String rangeHeader) throws IOException {

HTTP range requests in Spring

http-range streaming file-io

Advanced 10 steps

java

public List<int[]> merge(int[][] intervals) {
    if (intervals.length == 0) {
        return new ArrayList<>();
    }

Merging overlapping intervals in Java

intervals sorting greedy

Intermediate 7 steps

java

@Configuration
public class UserImportJobConfig {
 
    @Bean

How a Spring Batch CSV import job is wired

batch processing chunk oriented fault tolerance

Intermediate 10 steps

java

public final class BomAwareReader {
 
    private static final char UTF8_BOM = '\uFEFF';

Skipping the UTF-8 byte-order mark in Java

file-io encoding byte-order-mark

Intermediate 6 steps

java

public final class HmacJwt {
 
    private static final ObjectMapper MAPPER = new ObjectMapper();
    private static final Base64.Encoder ENCODER = Base64.getUrlEncoder().withoutPadding();

How HMAC-signed JWTs are created and verified

jwt hmac cryptography

Intermediate 9 steps

java

public final class MultipartParser {
 
    public record FilePart(String name, String filename, String contentType, byte[] content) {}

Parsing multipart form data by hand in Java

parsing byte-arrays http

Advanced 8 steps

java

@AutoConfiguration
@EnableConfigurationProperties(RateLimiterProperties.class)
@ConditionalOnClass(RateLimiter.class)
public class RateLimiterAutoConfiguration {

Building a Spring Boot rate-limiter auto-config

auto-configuration conditional-beans rate-limiting

Intermediate 7 steps

java

import java.math.BigDecimal;
import java.math.RoundingMode;
import java.util.Currency;

A safe Money value type in Java

immutability bigdecimal value-object

Intermediate 10 steps

java

public class RequestCoalescer<K, V> {
 
    private final ConcurrentHashMap<K, CompletableFuture<V>> inFlight = new ConcurrentHashMap<>();
    private final Function<K, V> loader;

Coalescing duplicate requests in Java

concurrency caching completablefuture

Advanced 6 steps

java

public final class NaturalOrderComparator implements Comparator<String> {
 
    public static final NaturalOrderComparator INSTANCE = new NaturalOrderComparator();

Natural-order string sorting in Java

comparator natural-sort string-parsing

Intermediate 9 steps

java

package com.example.validation;
 
import java.util.List;
import java.util.stream.Collectors;

Validating JSON payloads against a schema in Java

json-schema validation recursion

Intermediate 8 steps

java

public URI buildSearchUri(String query, int page, int size, List<String> tags) {
    UriComponentsBuilder builder = UriComponentsBuilder
            .fromUriString("https://api.example.com")
            .path("/v2/products/search")

Building URIs safely with UriComponentsBuilder in Spring

url-building builder-pattern encoding

Intermediate 5 steps

java

@Configuration
@EnableWebSocketMessageBroker
public class WebSocketConfig implements WebSocketMessageBrokerConfigurer {

Real-time chat over STOMP WebSockets in Spring

websockets stomp messaging

Intermediate 8 steps