Spring Boot

How long a bean lives, and the two moments the container promises to call you at.

One shape for every error response, wherever it comes from.

Two different answers to what an object mapped to a row actually is.

The four states an entity moves through, and the operations that move it.

What `@Transactional` actually wraps, and the two ways it surprises people.

Skipping work you've already done, on purpose, and knowing when to throw the answer away.

What the container actually is, and the five things it does to every bean before it's ready to use.

What Boot changes about starting a Spring application, and how it decides what to create for you.

One dependency instead of a dozen, and a server that ships inside the jar.

Where a setting comes from, and what wins when two sources disagree.

Turning a URL and a verb into a method call, and a method's return value into a response.

Refusing a bad request before it reaches your business logic.

Asking for data without writing the SQL yourself.

Finding the real bottleneck before optimizing the wrong thing.

Getting your dependencies handed to you — by constructor, and by name when there's more than one candidate.

Why Spring hands you your dependencies instead of you building them yourself.