Spring Framework & Spring Boot

Dependency injection, Spring Boot applications, REST controllers, validation, error handling and configuration.

This section is being written. There are no lessons in it yet: below is the plan for what it will cover. It opens in the syllabus as soon as its first lessons are ready.

What you will be able to do

Explain inversion of control and dependency injection and use them in Spring
Create a Spring Boot application and understand what auto-configuration does
Build REST controllers with request validation and consistent error responses
Organise code into controller, service and repository layers
Configure an application with properties, profiles and logging
Turn ShopLite into a Spring Boot REST API documented with OpenAPI

What it will cover

15.1Why Spring?
The problems Spring solves and how the Spring family fits together.
- Tight coupling and the new keyword
- Inversion of control in plain words
- Spring Framework vs Spring Boot
- Creating a project with Spring Initializr
- Project layout and the main class
15.2Dependency Injection & Beans
Let Spring create your objects and wire them together.
- Beans and the application context
- @Component, @Service, @Repository and @Controller
- Constructor injection and why to prefer it
- @Configuration and @Bean
- Several implementations: @Qualifier and @Primary
- Bean scopes and lifecycle callbacks
15.3How Spring Boot Works
What happens when a Spring Boot application starts.
- Starters and dependency management
- Auto-configuration and @SpringBootApplication
- Component scanning
- The embedded Tomcat server
- Reading the startup log
- Spring Boot DevTools
15.4Building REST Controllers
Expose endpoints that accept and return JSON.
- @RestController and @RequestMapping
- @GetMapping, @PostMapping, @PutMapping, @PatchMapping, @DeleteMapping
- @PathVariable, @RequestParam and @RequestBody
- ResponseEntity and status codes
- Request and response DTOs
- Returning 201 Created with a Location header
15.5Layered Architecture in Spring
Split an application into controller, service and repository layers with clear jobs.
- What belongs in each layer
- Mapping between entities and DTOs
- An in-memory repository before the database
- Package by layer vs package by feature
- Common layering mistakes
15.6Validation
Reject bad input at the edge of the application with clear messages.
- Bean Validation: @NotNull, @NotBlank, @Size, @Email, @Min, @Pattern
- @Valid on request bodies
- Validating path and query parameters
- Writing a custom validator
- Validation in the service layer for business rules
15.7Exception Handling
Return one consistent error format instead of stack traces.
- Default Spring error responses
- Custom exceptions such as NotFound and Conflict
- @RestControllerAdvice and @ExceptionHandler
- Validation error responses with field details
- ProblemDetail and RFC 7807 errors
15.8Configuration, Profiles & Logging
Change behaviour between development and production without changing code.
- application.properties vs application.yml
- @Value and @ConfigurationProperties
- Profiles: dev, test and prod
- Environment variables and secrets
- Logging with SLF4J: levels and what to log
- Health checks with Spring Boot Actuator
15.9API Documentation with OpenAPI
Generate interactive API docs that other developers can try out.
- What OpenAPI and Swagger UI are
- Adding springdoc-openapi
- Describing endpoints, parameters and responses
- Testing your API from Swagger UI
15.10Spring Boot Mini Project: ShopLite REST API
Rebuild ShopLite as a Spring Boot REST API, reusing the JDBC DAOs through JdbcTemplate.
- From DAO classes to JdbcTemplate repositories
- Product, customer and order endpoints
- Validation and global error handling
- Dev and prod profiles with PostgreSQL
- OpenAPI docs and a Postman collection

Start with what’s live

These sections are ready to study now.

See the whole roadmap

What you will be able to do

Explain inversion of control and dependency injection and use them in Spring

Create a Spring Boot application and understand what auto-configuration does

Build REST controllers with request validation and consistent error responses

Organise code into controller, service and repository layers

Configure an application with properties, profiles and logging

Turn ShopLite into a Spring Boot REST API documented with OpenAPI

What it will cover

15.1Why Spring?

The problems Spring solves and how the Spring family fits together.

Tight coupling and the new keyword
Inversion of control in plain words
Spring Framework vs Spring Boot
Creating a project with Spring Initializr
Project layout and the main class

15.2Dependency Injection & Beans

Let Spring create your objects and wire them together.

Beans and the application context
@Component, @Service, @Repository and @Controller
Constructor injection and why to prefer it
@Configuration and @Bean
Several implementations: @Qualifier and @Primary
Bean scopes and lifecycle callbacks

15.3How Spring Boot Works

What happens when a Spring Boot application starts.

Starters and dependency management
Auto-configuration and @SpringBootApplication
Component scanning
The embedded Tomcat server
Reading the startup log
Spring Boot DevTools

15.4Building REST Controllers

Expose endpoints that accept and return JSON.

@RestController and @RequestMapping
@GetMapping, @PostMapping, @PutMapping, @PatchMapping, @DeleteMapping
@PathVariable, @RequestParam and @RequestBody
ResponseEntity and status codes
Request and response DTOs
Returning 201 Created with a Location header

15.5Layered Architecture in Spring

Split an application into controller, service and repository layers with clear jobs.

What belongs in each layer
Mapping between entities and DTOs
An in-memory repository before the database
Package by layer vs package by feature
Common layering mistakes

15.6Validation

Reject bad input at the edge of the application with clear messages.

Bean Validation: @NotNull, @NotBlank, @Size, @Email, @Min, @Pattern
@Valid on request bodies
Validating path and query parameters
Writing a custom validator
Validation in the service layer for business rules

15.7Exception Handling

Return one consistent error format instead of stack traces.

Default Spring error responses
Custom exceptions such as NotFound and Conflict
@RestControllerAdvice and @ExceptionHandler
Validation error responses with field details
ProblemDetail and RFC 7807 errors

15.8Configuration, Profiles & Logging

Change behaviour between development and production without changing code.

application.properties vs application.yml
@Value and @ConfigurationProperties
Profiles: dev, test and prod
Environment variables and secrets
Logging with SLF4J: levels and what to log
Health checks with Spring Boot Actuator

15.9API Documentation with OpenAPI

Generate interactive API docs that other developers can try out.

What OpenAPI and Swagger UI are
Adding springdoc-openapi
Describing endpoints, parameters and responses
Testing your API from Swagger UI

15.10Spring Boot Mini Project: ShopLite REST API

Rebuild ShopLite as a Spring Boot REST API, reusing the JDBC DAOs through JdbcTemplate.

From DAO classes to JdbcTemplate repositories
Product, customer and order endpoints
Validation and global error handling
Dev and prod profiles with PostgreSQL
OpenAPI docs and a Postman collection