☕ Java Backend Engineering Roadmap

Rebuilding my career as a Java Backend Developer — from fundamentals to production-grade, in public.

🚀 Roadmap · 🧱 Tech Stack · 📁 Structure · 🏗️ Final Project · 📊 Progress

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👋 About This Repository

I'm Badru, a former Java Backend Developer. After time away from the field working other jobs, I'm rebuilding my skills from the ground up — not from zero knowledge, but from zero current practice — toward a modern, cloud-native, AI-aware Java backend stack.

This repository is my public learning log and portfolio: every concept gets a written explanation, every topic gets working code, and every milestone gets a commit. No copy-pasted tutorials without understanding — every folder here reflects something I can actually explain and defend.

Career target: Java Backend Engineer → Cloud-Native Backend Engineer → AI-enabled Backend Engineer

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🧱 Tech Stack

Layer	Technology	Priority
Language	Java 25 (LTS)	🔴 Must
Build Tool	Maven	🔴 Must
Framework	Spring Boot 4.1 · Spring Framework 7	🔴 Must
Data Access	Spring Data JPA · Hibernate	🔴 Must
Security	Spring Security · JWT	🔴 Must
Database	PostgreSQL 18	🔴 Must
Cache	Redis	🔴 Must
Messaging	Apache Kafka	🟡 Should
Testing	JUnit 5 · Mockito · Testcontainers	🔴 Must
Containerization	Docker · Docker Compose	🔴 Must
CI/CD	GitHub Actions	🟡 Should
Cloud	AWS (EC2 · RDS · S3 · IAM)	🟡 Should
Observability	Spring Actuator · Prometheus · Grafana	⚪ Awareness
Architecture	SOLID · Layered · Modular Monolith → Microservices	🔴 Must
AI Integration	Spring AI · LLM API · RAG basics	🟡 Should

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🗺️ Roadmap

A structured 30-day plan across 20 phases — from raw fundamentals to a production-shaped final project.

Click to expand full 30-day table

Day	Phase	Focus	Key Output
1	P0 · Environment & Git	JDK 25, IntelliJ, Git/GitHub, SSH	Repo initialized
2	P1 · Programming Fundamentals	Compiler, JVM/JDK/JRE, first program	Hello World+
3	P1 · Programming Fundamentals	Variables, data types, operators	CLI calculator
4	P1 · Programming Fundamentals	Conditionals & loops	FizzBuzz & variants
5	P2 · Java Fundamentals	Methods, arrays	Refactored calculator
6	P2 · Java Fundamentals	Collections: List, Set, Map, generics	In-memory CRUD
7	P2 · Java Fundamentals	Exceptions, packages, access modifiers	Error-handled program
8	P3 · OOP	Classes, objects, encapsulation	First domain model
9	P3 · OOP	Inheritance, polymorphism, interfaces	Class hierarchy
10	P3 · OOP	Composition, SOLID principles	Refactored domain code
11	P4 · Modern Java	Lambdas, functional interfaces, Streams	Stream-based refactor
12	P4 · Modern Java	Records, enums, Date/Time, concurrency basics	Record-based DTOs
13	P5 · SQL & PostgreSQL	Relational modeling, keys, normalization	ERD + schema
14	P5 · SQL & PostgreSQL	CRUD queries, JOINs	Query set
15	P5 · SQL & PostgreSQL	Aggregates, indexing, transactions, ACID	Optimized queries
16	P6 · HTTP & REST	HTTP methods, status codes, REST principles	API contract (OpenAPI)
17	P7 · Spring Boot	DI, IoC, Beans, first Spring Boot app	hello-spring project
18	P7 · Spring Boot	REST Controllers, DTOs, validation	Product CRUD API
19	P8 · Spring Data JPA	Entities, repositories, relationships	API + PostgreSQL
20	P8 · Spring Data JPA	N+1 problem, pagination, JPQL	Optimized API
21	P9 · Spring Security	Auth vs authz, JWT, filter chain	API with auth
22	P10 · Testing	Unit & integration testing, Testcontainers	Test suite
23	P11 · Docker	Dockerfile, multi-stage build, Compose	docker compose up works
24	P12 · Redis	Cache-aside, TTL, invalidation	Cached endpoints
25	P13 · Kafka	Producers, consumers, topics, partitions	Event flow demo
26	P14–15 · Microservices & AWS	Service boundaries, EC2/RDS/S3 basics	Architecture notes
27	P16–17 · CI/CD & Observability	GitHub Actions, Actuator, logging	Working CI pipeline
28	P18 · System Design	Scalability, load balancing, CAP theorem	System design doc
29	P19 · AI Integration	LLM basics, Spring AI, RAG concepts	AI feature shipped
30	P20 · Portfolio & Interview Prep	README polish, mock interviews, CV	Portfolio finalized

Learning depth by topic:

• 🔴 MUST LEARN — Java (fundamentals → modern), OOP, SQL/PostgreSQL, REST, Spring Boot Core/MVC/JPA, Spring Security basics, testing basics, Docker basics.
• 🟡 SHOULD LEARN — Redis, Kafka basics, CI/CD, AWS fundamentals, AI integration.
• ⚪ AWARENESS ONLY — full microservices, observability stack, advanced distributed systems, advanced AWS networking.

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📁 Repository Structure

java-backend-engineering-roadmap/
├── README.md
├── LICENSE
├── .gitignore
├── .editorconfig
├── .github/
│   └── workflows/
│       └── ci.yml
├── docs/
│   ├── roadmap/
│   ├── architecture/
│   ├── interview/
│   ├── cheatsheets/
│   └── progress/
│       └── PROGRESS.md
├── 00-environment/
├── 01-programming-fundamentals/
├── 02-java-fundamentals/
├── 03-oop/
├── 04-modern-java/
├── 05-sql-postgresql/
├── 06-http-rest/
├── 07-spring-boot/
├── 08-spring-data-jpa/
├── 09-spring-security/
├── 10-testing/
├── 11-docker/
├── 12-redis/
├── 13-kafka/
├── 14-microservices/
├── 15-aws/
├── 16-cicd/
├── 17-observability/
├── 18-system-design/
├── 19-ai-integration/
├── projects/
│   └── final-project/          # Order Management System
└── portfolio/
    ├── index.html
    ├── style.css
    └── script.js

Folder	Purpose
0X-topic/	Daily learning notes — each sub-topic has its own README.md + practice code
docs/roadmap/	This roadmap, versioned as it evolves
docs/architecture/	Final project architecture diagrams
docs/interview/	Mock interview notes & weak points to revisit
docs/cheatsheets/	Quick-reference sheets (Git, SQL syntax, etc.)
docs/progress/PROGRESS.md	Milestone checklist, updated after every completed day
projects/final-project/	The one serious project: Order Management System
portfolio/	Standalone landing page showcasing this journey
.github/workflows/	CI pipeline definitions

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🏗️ Final Project — Order Management System

Built as a Modular Monolith first, then selectively decomposed into services — to demonstrate understanding of when microservices are actually needed, not just how to use them.

Client (Postman / simple frontend)
        │  HTTP / REST
        ▼
┌─────────────────────────────────────┐
│         Spring Boot Application       │
│  ┌────────┐ ┌────────┐ ┌───────────┐ │
│  │  auth  │ │  user  │ │ inventory │ │
│  └────────┘ └────────┘ └───────────┘ │
│  ┌────────┐ ┌────────┐ ┌───────────┐ │
│  │ order  │ │payment │ │    ai     │ │
│  └────────┘ └────────┘ └───────────┘ │
└──────┬──────────┬──────────┬─────────┘
       ▼           ▼          ▼
  PostgreSQL     Redis      Kafka

Features: JWT authentication & authorization · product/inventory management · order processing · simulated payments · Redis caching · Kafka event-driven notifications · AI-generated product descriptions · full test coverage · Dockerized · CI pipeline.

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🛠️ Tools & Setup

Tool	Version	Required
JDK	25 (LTS)	✅
IntelliJ IDEA	Latest	✅
Git	Latest	✅
Maven	Latest	✅
Docker Desktop / Engine	Latest	✅
PostgreSQL	18 (via Docker)	✅
Postman / Bruno	Latest	✅
Redis	Latest (via Docker)	🟡
Kafka	Latest (via Docker Compose)	🟡

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📝 Commit Convention

This repository follows Conventional Commits — every commit maps to a clear milestone.

feat(java): add variables and operators fundamentals
docs(git): add git workflow guide
feat(api): implement order creation endpoint
test(order): add order service unit tests
fix(security): correct JWT expiration handling
chore(deps): upgrade spring boot to 4.1

Type	Use for
feat	New feature or learning module
fix	Bug fix
docs	Documentation changes
refactor	Code change with no behavior change
test	Adding or updating tests
chore	Tooling, dependencies, config

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📊 Progress Tracker

• Java Fundamentals
• OOP
• Modern Java (Streams, Records)
• SQL & PostgreSQL
• HTTP & REST
• Spring Boot Core & MVC
• Spring Data JPA
• Spring Security
• Testing
• Docker
• Redis
• Kafka
• Microservices & AWS Basics
• CI/CD
• System Design
• AI Integration
• Final Project — Order Management System

Full detail tracked in docs/progress/PROGRESS.md.

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📬 Connect

GitHub: @rubyske

Rebuilding, one commit at a time.