Name: Knock Knock, Who's There? HTTP Status Codes Explained with Quarkus
Author: Luiz Henrique de Sousa Ribas

Cover of Knock Knock, Who’s There? HTTP Status Codes Explained with Quarkus

Luiz Henrique de Sousa Ribas

Coming soon · 2026Open access · CC BY 4.0

Every time a computer asks another computer for something on the web, the answer comes back with a three-digit number. This book explains those numbers, the HTTP status codes, so simply that a 10-year-old can follow, and so accurately that a professional can rely on it.

The whole book takes place in the Internet Restaurant, where Clara the Client orders, Sam the Server cooks, and every plate comes back with a number on it. Each code is shown in a small application you can run, and the last two chapters use everything you have learned to understand, and then build, an API Gateway.

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Companion code: github.com/lhsribas/httpstatus-code-explained-with-quarkus

Who this book is for

Curious beginners who want to know what really happens when an app talks to the internet
Students and new developers who build or call APIs and keep meeting codes like 401, 404 and 503
Java developers who want to see how each code is produced, before they learn about API Gateways

The Internet Restaurant
Three-Digit Answers
Your Java Playground
1xx Informational, “Hold On…”
2xx Success, “Here You Go!”
3xx Redirection, “Look Over There”
4xx Client Errors, Part 1, “It’s You”
4xx Client Errors, Part 2, “Not Like That”
5xx Server Errors, “It’s Us”
Picking the Right Code
Meet the API Gateway
Build a Tiny API Gateway in Java

Appendices: every registered status code, glossary, sources and further reading.

About the author

Luiz Henrique de Sousa Ribas is a Principal Technical Architect at WP Engine in Dublin, working on the company’s edge platform: Cloudflare, multi-CDN delivery and edge security. Before WP Engine he worked at Accenture, Avanade and Red Hat, where at Red Hat Open Innovation Labs he wrote the Where to Start practice for the Open Practice Library. He began his career as a developer and has a deep background in Java, APIs, containers, Kubernetes and OpenShift. He is a member of the editorial board of the Journal of Intelligent Systems and Applied Technology (JISAT).