Java, Spring Boot & Microservices Interview Prep

This guide teaches you how the technology really works, then shows how interviewers test it. Every topic follows the same ten parts, starting with a short definition in plain words.

Every page has a short intro, concepts explained plainly, code examples, Mermaid diagrams, common interview questions with model answers, pitfalls and key takeaways. Code samples were compiled and run wherever they could be (the Java, SQL, Spring, Kafka and Redis examples were executed; infrastructure manifests are illustrations, and each page says so when something was not run).

What is inside

Section	What you will learn	Start with
Java	Collections internals, generics, streams, Java 8 to 25 features, concurrency, memory model, GC, JVM diagnostics, virtual threads	HashMap internals
Spring Framework	IoC and AOP, bean lifecycle, Spring Boot internals, testing, JPA, transactions, locking, caching, Spring Security, JWT and OAuth2	Spring Boot overview
Microservices	Decomposition, gateway, discovery, config, Resilience4j, saga, CQRS, outbox and idempotency, observability	Microservices overview
Databases	Relational design, ACID and MVCC, SQL patterns, replication and sharding, NoSQL and Redis, zero-downtime migrations	ACID and MVCC
Messaging	Kafka architecture, consumer groups and delivery semantics, ordering and dead-letter design, RabbitMQ	Kafka fundamentals
DevOps and Cloud	Docker for Java, Kubernetes, CI/CD, twelve-factor apps, deployment strategies	Docker for Java
System Design	A framework and worked designs: URL shortener, rate limiter, order processing, notification service, trade-offs	Approach and estimation
Interview Toolkit	100 interview questions, STAR answers, 16 coding problems with tested solutions, cheat sheets	Cheat sheets

Where to start

• New to the stack: begin with OOP, the collections framework and Spring IoC, then drill questions 1-35.
• Going deeper: Spring internals, transactions and microservices patterns, then questions 36-70.
• Architecture and trade-offs: JVM diagnostics, distributed consistency, system design and behavioural stories, then questions 71-100.
• Short on time: skim the cheat sheets.

How to use a page

1. Read once for the concepts.
2. Close it and explain the topic aloud, then try the interview questions.
3. Re-read the pitfalls: this is where most candidates lose marks.
4. Reproduce one example yourself (an N+1, a deadlock, a stuck consumer) and break it deliberately.

Found an error or want a topic added? Contact me.