Spring Boot Mastery Path¶

Mastery Path

BOOTCAMP

VINOD BHANUJA

Spring Boot is how a very large share of the Java world builds backend services. Under the hood it is the Spring Framework — an inversion-of-control container that creates your objects, wires them together, and wraps them in proxies that add transactions, security, and caching — plus an opinionated layer that configures all of that for you based on what is on your classpath. Put spring-boot-starter-webmvc in your build and you get an embedded Tomcat, JSON serialization, and a dispatcher servlet without writing a line of setup. That convenience is also the main source of confusion: when something behaves unexpectedly, the answer is usually in a bean, proxy, or auto-configuration you never saw.

This course teaches you to build real services with Spring Boot and to see through the magic. It assumes you already know Java — classes, interfaces, generics, lambdas, records, exceptions, and a build tool at a basic level. If you do not, start with the Java Mastery Path, which covers the language itself; here we spend no time on Java syntax.

Level 1 builds a REST API with validation, error responses in the standard application/problem+json format, typed configuration, and logging. Level 2 adds a real database through Spring Data JPA and Hibernate, Flyway migrations, transactions, a proper test suite, and Spring Security with JWTs. Level 3 opens the machinery — how auto-configuration decides what to create, how AOP proxies implement @Transactional and @Cacheable, why lazy loading causes N+1 queries — and adds caching, async work, Kafka messaging, resilient HTTP clients, and Actuator. Level 4 is about running services for real: microservices and Spring Cloud, WebFlux versus virtual threads, performance, native images, containers, tracing, hardening, deployment, and a capstone.

Every lesson ends with a How It Actually Works section that explains the mechanism rather than just the annotation: the proxy behind @Transactional and why calling a transactional method from the same class silently skips the transaction, the @Conditional checks that decide which auto-configurations apply, the bean lifecycle from definition to destruction, and Hibernate's persistence context with its dirty checking.

About versions and outputs

Code in this course targets Spring Boot 4.x (the line Spring Initializr generates today, built on Spring Framework 7) with Java 17 or newer — Java 21 or 25 is recommended so you can use virtual threads. Boot 3.x is still widespread in existing codebases and nearly everything here applies to it too; where Boot 4 changed a name or package (for example the spring-boot-starter-webmvc starter or the test-slice packages), the lesson points out the 3.x equivalent. Builds use Maven; Gradle equivalents are shown where they differ in an interesting way. Console output shown in lessons was produced by actually running the code; where something needs an external service (PostgreSQL, Kafka, an identity provider, a cloud platform) and it was not run for this course, the lesson says so rather than inventing output.

How the program is organized¶

Level	Focus	Modules
Level 1 · Entry	What Spring is, Initializr & project layout, dependency injection, beans & scanning, configuration & profiles, REST controllers, validation, error handling, logging	9 topics + 1 project (task tracker API)
Level 2 · Intermediate	Spring Data JPA & Hibernate, entities & relationships, repositories & queries, transactions, Flyway, testing, Spring Security, JWT resource server, OpenAPI docs	9 topics + 1 project (secured library API)
Level 3 · Advanced	Auto-configuration internals, AOP & proxies, N+1 & fetch strategies, caching, async & scheduling, Kafka, HTTP clients & resilience, Actuator, bean lifecycle & events	9 topics + 1 project (event-driven order service)
Level 4 · Master	Spring Cloud & microservices, WebFlux vs virtual threads, performance, GraalVM native, containers, observability, security hardening, deployment, modular architecture	9 topics + 1 capstone (production-ready service)

How to use this site¶

Work through the levels in order. Level 3 explains why the annotations you used in Levels 1 and 2 behave the way they do, and it lands much better once you have been surprised by them at least once.
Build the code. Generate a project from start.spring.io, paste the classes in, and run ./mvnw spring-boot:run or ./mvnw test. Break things on purpose — remove an annotation, rename a property — and read the startup failure.
Do the Exercise at the end of each lesson. Each project (module 10) grows out of the exercises before it.
Keep one repository per level. By the end you will have a validated REST API, a secured database-backed service with tests, an event-driven service using Kafka, and a containerized, observable capstone.
For the language itself, see the Java Mastery Path; for testing in depth, Java Testing; for the architecture side, the System Design Mastery Path.