Learn Microservices with Spring Boot Labs

Monolith-first to microservices with Spring Boot, test-driven development, event-driven systems, common architecture patterns, nonfunctional requirements, and end-to-end testing with Cucumber.

A Basic Spring Boot Application

User Story 1

As a user of the application, I want to solve a random multiplication problem using mental calculation so I exercise my brain.

Tasks

1. Create a basic service with business logic.
2. Create a basic API to access this service (REST API).
3. Create a basic web page to ask the users to solve that calculation.

Generate the project skeleton with Lombok, Spring Web, and Validation: Spring Initializr with Java 8, Gradle, Spring Boot 2.4.5

Three-Tier Three-Layer Architecture

• Client tier: user interface
• Application tier: business logic, interfaces, and the data interfaces for persistence.
• Data store tier: persists the application's data (e.g. Database, file system, etc.)

Application Tier Layers

The application tier is made up of the following layers:

• Business Layer - Classes that model the domain
• Presentation Layer - Controller classes that implement the REST API
• Data Layer - Persists entities with Data Access Objects (DAO) or Repoistories (Domain)
• Domain Layer - Domain is isolated and independent of everything else

Spring Annotations

Three stereotype annotations that map to each of layers:

• @Controller - Presentation Layer, used for the REST API
• @Service - Business Layer for business logic
• @Repository - Data Layer, classes that interact with the Database

When we annotate classes with these variants, they become Spring-managed components.

• When initializing the web context, Spring scans your packages and loads them as beans
• We can use dependency injection to wire (or inject) these beans and use services from our presentation layer (controllers)

Domain Modeling

Start by modeling the business domain to structure the project:

• Challenge - The math problem
• User - The user
• Challenge Attempt - The attempt by the user to solve the math problem

Relationships

• Challenge and User are independent
• Challenge Attempts reference a User and a Challenge

Bounded Contexts

• User
• Challenge

Domain Layer

• microservices.book.multiplication.user.User
• microservices.book.multiplication.Challenge
• microservices.book.multiplication.challenge.ChallengeAttempt

Business Layer

• Functionality to generate a multiplication problem
• Functionality to check whether an attempt is correct

Presentation Layer

REpresentational State Transfer (REST) - Uses HTTP verbs to perform API operations:

HTTP Verb	Operation on Collection	Operation on Item
GET	Gets full list of items	Get the item
POST	Creates a new item	Not Applicable
PUT	Not Applicable	Updates the item
DELETE	Deletes the full collection	Deletes the item

REST APIs with Spring Boot use the following annotations:

• @RestController - specialization of @Controller
• @RequestBody - Used to pass body of request to method and Spring will deserialize custom class to JSON
• @RequestMapping - Model resources and verbs at class and method level and spring provides variants
  • @GetMapping - Get
  • @PostMapping - Create
  • @PutMapping - Update
  • @DeleteMapping - Delete

API Design

• An interface to get a random multiplication problem
  • GET /challenges/random
• An endpoint to send a guess for a given multiplication problem from a user alias
  • POST /attempts
• Both resources belong to the challenges domain