Spring Boot

Beans, auto-configuration, MVC, validation, Data JPA, transactions, N+1, caching, security, actuator and test slices, each mechanism modelled as plain Java you can run.

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In this course

The IoC container and dependency injectionWhat the ApplicationContext actually does at startup — read bean definitions, build each singleton after its dependencies, and inject the same instance everywhere.9 min
Bean scopes, and the prototype that stopped being oneSingleton, prototype and the web scopes — and why a prototype injected into a singleton is created exactly once.9 min
Auto-configuration, starters and conditions that back offHow Spring Boot decides which beans to create for you — candidates from the classpath, conditions on each, and your own beans always winning.10 min
Externalized configuration, precedence and profilesWhere a property's value really comes from — the precedence order, environment-variable names, typed @ConfigurationProperties, and how profiles layer on top.10 min
Spring MVC and REST controllersHow DispatcherServlet turns a request into a method call — mapping, argument binding, message conversion — and which status you get when nothing matches.10 min
Validation and exception handlingBean Validation on request bodies, the null rules behind @NotNull, @NotEmpty and @NotBlank, and how Spring picks the @ExceptionHandler that turns an exception into a status.11 min
Spring Data JPA repositories and derived queriesAn interface with no implementation that still runs queries — how Spring Data derives them from method names, and what Page and Slice cost.10 min
The persistence context, dirty checking and flushWhy an update happens without save(), why two finds cost one SELECT, and why Hibernate can insert before it deletes.11 min
@Transactional is a proxy: self-invocation and other trapsThe annotation does nothing by itself — a proxy around the bean starts and ends the transaction, so a call that skips the proxy skips the transaction.10 min
Propagation and rollback rulesREQUIRED versus REQUIRES_NEW, why a checked exception commits, and the UnexpectedRollbackException you get for catching an exception from a joined transaction.11 min
Lazy loading and the N+1 problemWhat a lazy association really is, why a loop over twenty orders can send twenty-one queries, and the fixes — fetch joins, entity graphs and batch fetching.11 min
Caching with @Cacheable, @CachePut and @CacheEvictSpring's cache abstraction as a proxy around a method — how keys are built, when the method body is skipped, and the stale and colliding entries that follow.10 min
Spring Security: the filter chain, 401 and 403Security runs as servlet filters before any controller; authorization rules are checked in order and the first match decides, and the response says whether you are unknown or merely not allowed.10 min
JWT authentication for a stateless APIWhat is inside a JWT, what its signature does and does not protect, how a Spring resource server validates one, and why revoking one is hard.12 min
Actuator, health checks and metricsThe production endpoints Spring Boot gives you, which of them are exposed by default, how health is aggregated into one status, and what Micrometer records.10 min
Testing with Spring Boot test slicesWhen to start the whole application and when to start a slice of it, what each slice loads, and how the test context cache makes or breaks suite speed.11 min