Curriculum & Resources

What to learn, and where

The from-scratch Java Backend map, ruthlessly prioritised. Each topic points to the single best 2026 resource. Tick what you've learned.

☕ Core Java P0

From zero syntax to streams & concurrency. The language everything else is built on.

▶ Start hereTelusko — Java Full Course (YouTube) ↺ If stuckTim Buchalka — Java Masterclass (Udemy, on sale only) 📖 Docsdev.java/learn — Oracle official tutorials ⌨ PracticeExercism Java + CodingBat

○ Setup: JDK 21, IntelliJ, run a program P0 L2 deep dive →

○ Variables, types, operators, I/O, control flow P0 L2

○ Methods, parameters, return values P0 L2

○ OOP: classes, objects, constructors, encapsulation P0 L4 deep dive →

○ Inheritance, polymorphism, abstraction, interfaces P0 L4 deep dive →

○ Strings, StringBuilder, arrays P0 L2

○ Collections: List, Set, Map, Queue, Deque P0 L4 deep dive →

○ equals/hashCode, Comparable, Comparator P0 L4 deep dive →

○ Exceptions (checked/unchecked, try-with-resources) P0 L4 deep dive →

○ Generics (bounded wildcards) P0 L4 deep dive →

○ Enums, static/final, access modifiers, records P0 L2

○ Lambdas, functional interfaces, Streams, Optional P0 L4 deep dive →

○ Concurrency: threads, Executors, synchronized, virtual threads P1 L4 deep dive →

○ JVM / memory / GC basics (heap vs stack, OOM vs SO) P1 L4 deep dive →

🧩 DSA (Java) P0

Patterns → understanding → repetition → timed practice. ~146 problems, not 450. Skip the Hard tier.

▶ Start hereNeetCode Roadmap + NeetCode 150 ↺ If stuckStriver's A2Z DSA Sheet (takeUforward) 📖 DocsJava Collections Framework ⌨ PracticeYour 146 tracker → LeetCode

○ Big-O: time & space complexity P0 L4 deep dive →

○ Arrays & Hashing P0 L4 deep dive →

○ Two Pointers P0 L4 deep dive →

○ Sliding Window P0 L4 deep dive →

○ Prefix Sums P1 L2

○ Stack & Queue P0 L4 deep dive →

○ Binary Search P0 L4 deep dive →

○ Sorting P1 L2

○ Linked Lists P0 L4 deep dive →

○ Trees & BST (BFS/DFS) P0 L4 deep dive →

○ Heap / Priority Queue P1 L4 deep dive →

○ Graphs (BFS/DFS, topo, union-find) P1 L3

○ Dynamic Programming (1-D basics) P1 L3 deep dive →

🗄️ SQL & DBMS P0

Fluent SQL + interview-level DBMS. Window functions are the differentiator at this band. Not DBA level.

▶ Start herefreeCodeCamp SQL Full Course (or Mosh SQL) ↺ If stuckMode SQL Tutorial (window functions, CTEs) 📖 DocsPostgreSQL documentation ⌨ PracticeLeetCode SQL 50 + SQLBolt

○ DB, table, row, column, primary/foreign key P0 L4 deep dive →

○ SELECT, WHERE, ORDER BY, GROUP BY, HAVING, DISTINCT, LIMIT P0 L4 deep dive →

○ INSERT, UPDATE, DELETE P0 L2

○ Joins: INNER, LEFT, RIGHT, SELF (heavily tested) P0 L4 deep dive →

○ Subqueries, CTEs, CASE, EXISTS, UNION P0 L4

○ Window functions (ROW_NUMBER, RANK, LAG/LEAD) P0 L4 deep dive →

○ Indexes, composite indexes, EXPLAIN basics P0 L4 deep dive →

○ Transactions, ACID, isolation levels, locks, deadlocks P0 L4 deep dive →

○ Normalization (1NF/2NF/3NF), when to denormalize P1 L4 deep dive →

○ SQL vs NoSQL — when to use each P1 L4 deep dive →

○ Replication / partitioning / sharding (concept only) P2 L1 deep dive →

🌐 How the Web Works P0

The backend foundation. What actually happens when you type a URL. Do this before Spring Boot.

▶ Start herefreeCodeCamp — HTTP Full Course ↺ If stuckroadmap.sh Backend — Internet section 📖 DocsMDN — HTTP ⌨ PracticeDevTools Network tab + curl -v

○ Client, server, request/response cycle P0 L4 deep dive →

○ HTTP methods + idempotency P0 L4 deep dive →

○ Status codes (200/201/204/400/401/403/404/409/500/502/503) P0 L4

○ Headers, cookies vs sessions vs JWT P0 L4

○ REST principles, JSON P0 L4 deep dive →

○ HTTPS/TLS (concept), DNS, TCP handshake P1 L2 deep dive →

○ "What happens when you type a URL" P1 L4 deep dive →

🌱 Spring Boot P0

Understand what Spring solves, then Core → MVC → Data JPA → Security. Concepts over annotations.

▶ Start hereSpring Academy — official, free, interactive ↺ If stuckJava Brains (concepts) + Amigoscode / Chad Darby 📖 Docsdocs.spring.io ⌨ PracticeBuild the Payment Platform API

○ What problem Spring solves (manual DI first) P0 L4 deep dive →

○ Spring Core: IoC, DI, beans, ApplicationContext, config P0 L4 deep dive →

○ Spring Boot: starters, auto-config, properties/yml, profiles P0 L2 deep dive →

○ Spring MVC: Controller, Service, Repository, DTO P0 L4 deep dive →

○ Validation (@Valid) + global exception handling P0 L4 deep dive →

○ Spring Data JPA: entities, repositories, relationships P0 L4 deep dive →

○ Lazy vs eager, transactions, pagination, JPQL, N+1 P0 L4 deep dive →

○ Spring Security 6: filter chain, UserDetails, BCrypt P0 L4 deep dive →

○ JWT auth flow, roles, @PreAuthorize, CORS/CSRF P0 L4 deep dive →

🧱 Backend Engineering P0

How to actually build systems: API design, idempotency, pagination, logging, async, queues.

▶ Start hereBaeldung — REST with Spring (free articles) ↺ If stuckZuplo API Design Patterns + Stripe API docs 📖 DocsSpring Guides ⌨ PracticeBuild it into the Payment Platform

○ REST API design, URI design, versioning P0 L4

○ DTOs, validation, consistent error JSON P0 L4

○ Pagination (offset + cursor), filtering, sorting P0 L4

○ Idempotency (keys for POST/payments) P1 L4

○ Rate limiting, retries + backoff, timeouts P1 L3 deep dive →

○ Structured logging + correlation IDs P1 L3

○ Sync vs async, background jobs, queues P1 L2

○ HATEOAS, GraphQL/gRPC, event sourcing/CQRS P3 L1

🧪 Testing P0

Turn your testing background into an edge. JUnit 5 + Mockito + Testcontainers.

▶ Start hereBaeldung — JUnit 5 + Mockito series ↺ If stuckAmigoscode testing videos 📖 DocsJUnit 5 + Testcontainers docs ⌨ PracticeTest the Payment Platform service layer

○ Why test? Unit vs integration vs E2E, the test pyramid P0 L4 deep dive →

○ JUnit 5 + AssertJ (assertThat, parameterized) P0 L2

○ Mockito (@Mock/@InjectMocks, when/verify) P0 L2

○ Spring Boot slices (@WebMvcTest, @DataJpaTest, MockMvc) P1 L2

○ Testcontainers (real PostgreSQL, @ServiceConnection) P1 L2

🐛 Debugging P1

Symptom → Hypothesis → Evidence → Root Cause → Fix → Regression Test. Your daily superpower.

▶ Start hereIntelliJ debugger docs + practice on real bugs ↺ If stuckBaeldung — Spring Boot logging & debugging 📖 DocsJava stack trace anatomy ⌨ PracticeDebug your own project failures

○ Read stack traces & logs P0 L3

○ Reproduce → hypothesis → evidence → root cause P0 L3

○ Breakpoints, inspect variables (IntelliJ) P0 L3

○ Debug APIs, SQL, Spring, Docker P1 L3

🔀 Git & GitHub P0

The 20% you use 80% of the time — plus PRs, branching, conflict resolution.

▶ Start herefreeCodeCamp — Git & GitHub Crash Course ↺ If stuckPro Git book (Branching + Rebasing) 📖 Docsgit-scm.com/docs + GitHub Docs ⌨ PracticeLearn Git Branching (interactive)

○ init/clone, add/commit, status/log, .gitignore P0 L2 deep dive →

○ branch/switch, push/pull, remotes P0 L2 deep dive →

○ Pull requests + conflict resolution P0 L3 deep dive →

○ merge vs rebase (never rebase shared branches) P1 L3 deep dive →

○ undo/recovery: reset, revert, stash P1 L3 deep dive →

🖥️ Operating Systems P1

Interview-relevant only. Processes, threads, memory, concurrency, deadlocks. Not an academic course.

▶ Start hereNeso Academy — OS playlist (watch selectively) ↺ If stuckGate Smashers — OS (India, interview-shaped) 📖 DocsOSTEP (free book — Concurrency pieces) ⌨ PracticeJava: cause a race condition, fix it, force a deadlock

○ Process vs thread, context switching P0 L4 deep dive →

○ Memory: stack/heap, virtual memory, paging P1 L4 deep dive →

○ Race conditions, mutex vs semaphore P0 L4

○ Deadlocks (Coffman conditions + prevention) P0 L4

📡 Networking P1

Backend & interview scoped. TCP/UDP, DNS, TLS, load balancers, proxies. Skip subnetting math.

▶ Start hereHussein Nasser — Fundamentals of Networking ↺ If stuckroadmap.sh Backend (coverage tracker) 📖 DocsCloudflare Learning Center ⌨ PracticeWireshark: capture one HTTPS request

○ OSI vs TCP/IP, TCP vs UDP P1 L4 deep dive →

○ DNS resolution flow, 3-way handshake P1 L4 deep dive →

○ TLS handshake (high level), ports & sockets P1 L2 deep dive →

○ Proxy vs reverse proxy, load balancer L4/L7, CDN P1 L4

🐧 Linux P2

Backend-relevant commands only. Install WSL2 and run everything as you learn.

▶ Start herefreeCodeCamp — 50 Most-Used Linux Commands ↺ If stuckThe Linux Command Line (free book) 📖 Docsman pages (built-in) ⌨ PracticeInstall WSL2 Ubuntu (wsl --install)

○ Navigation, file ops, permissions (chmod/chown, rwx) P2 L2

○ pipes, grep, ps/top/kill, tail -f logs P2 L2

○ ports (ss/lsof), curl, ssh P2 L2

○ systemctl, journalctl, env vars P2 L2

🐳 Docker P1

Images, containers, Dockerfile, Compose. The job-relevant skill: compose Spring + Postgres + Redis.

▶ Start hereTechWorld with Nana — Docker for Beginners ↺ If stuckDevOps with Docker (Univ. Helsinki, free) 📖 Docsdocs.docker.com ⌨ PracticeContainerize the Payment Platform

○ What Docker solves; images vs containers P1 L2 deep dive →

○ Write a Dockerfile (multi-stage for Java) P1 L2 deep dive →

○ Volumes, networks, env vars P1 L2 deep dive →

○ docker-compose: Spring + Postgres + Redis P1 L2 deep dive →

⚡ Redis & Caching P2

Why caching exists, cache-aside, TTL, invalidation — and when NOT to use it (interview gold).

▶ Start hereRedis University — Get Started (official, free) ↺ If stuckRedis Crash Course (freeCodeCamp) 📖 Docsredis.io/docs ⌨ PracticeWire @Cacheable into the project

○ What Redis is; why caching exists; key/value + TTL P2 L2

○ Cache-aside pattern + invalidation P1 L4 deep dive →

○ When NOT to cache; cache stampede, stale reads P1 L4

○ Sessions, rate limiting with Redis P2 L2

☁️ AWS P2

Junior backend scope, NOT certification. IAM, EC2, S3, RDS, CloudWatch. Set a billing alarm day one.

▶ Start herefreeCodeCamp AWS (EC2/S3/RDS/IAM/CloudWatch only) ↺ If stuckroadmap.sh AWS + AWS Skill Builder free 📖 Docsdocs.aws.amazon.com ⌨ PracticeAWS Free Tier (note: 2025 = $100 credits/6mo)

○ IAM: users/roles/policies, least privilege P1 L2 deep dive →

○ EC2 (launch, security groups, SSH) P2 L2

○ S3 (buckets, policies, presigned URLs) P2 L2 deep dive →

○ RDS (managed Postgres) + CloudWatch (logs, billing alarm) P1 L2 deep dive →

🏛️ System Design P1

Junior/mid depth. Requirements → API + DB → scale → cache → queues. Mention (not design) distributed internals.

▶ Start hereGaurav Sen — System Design (YouTube, free) ↺ If stuckByteByteGo (free YouTube + newsletter) 📖 DocsSystem Design Primer (GitHub, free) ⌨ Practice5 problems: URL shortener → rate limiter → notifications → file storage → payments

○ What is system design; functional vs non-functional reqs P1 L4 deep dive →

○ API + relational DB schema design; estimation P1 L4 deep dive →

○ Scaling (horizontal/vertical), load balancers P1 L4 deep dive →

○ Caching, message queues, read replicas, indexing P1 L4

○ CAP, sharding/partitioning (concept only) P1 L1

○ Consensus (Raft/Paxos), consistent hashing, Kafka internals P3 L1

🌍 Open Source P2

Quality > count. Read a repo → find a good-first-issue → make a real, merged PR.

▶ Start hereOpen Source Guides (by GitHub) ↺ If stuckFirst Contributions (safe practice repo) 📖 Docsgoodfirstissue.dev (find Java issues) ⌨ Practice1 typo PR → 1 real good-first-issue

○ What open source is; reading a repo (README→CONTRIBUTING→tests) P2 L2

○ Fork→clone→branch→commit→PR loop P2 L2

○ Find a good-first-issue; comment before starting P2 L2

○ Write a clear PR; respond to review feedback P2 L2

🎤 Interview Prep P1

DSA + Java/Spring + SQL + CS + HR + mocks. Mocks are the highest-ROI, most-skipped step.

▶ Start hereStriver's SDE Sheet + NeetCode 150 ↺ If stuckjavatpoint Spring Boot interview Qs + Gate Smashers CS 📖 DocsLeetCode SQL 50 + SQLBolt ⌨ PracticePramp / Exponent free mock interviews

○ DSA rounds (Medium mastery) P0 L4 deep dive →

○ Java + Spring concept questions P0 L4 deep dive →

○ SQL + CS fundamentals rapid review P0 L4

○ HR/behavioral (STAR, 6–8 stories, why-this-company) P1 L4

○ 3–5 mock interviews before real ones P0 L4