Simple Java Spring Boot Project

A minimal, production-ready-ish REST API built with Spring Boot 3.2.5 and Java 17. It ships with:

• GET /greeting — hello endpoint
• Book API (/api/books) — CRUD with JPA + H2, validation, proper HTTP semantics
• Actuator health endpoint, dev-friendly config, and tests

---

Tech stack

• Java 17
• Spring Boot 3.2.5
  • Web (Spring MVC)
  • Data JPA (Hibernate 6)
  • Validation (Jakarta Validation)
  • Actuator
• H2 (in-memory) for local/dev
• Maven

---

Project structure

app/
├─ src/
│  ├─ main/java/com/example/demo/
│  │  ├─ DemoApplication.java
│  │  ├─ GreetingController.java
│  │  ├─ adapter/web/controller/
│  │  │  └─ BookController.java
│  │  ├─ adapter/web/dtos/
│  │  │  └─ BookDtos.java
│  │  ├─ application/portout/repository/
│  │  │  └─ BookRepository.java
│  │  ├─ application/service/
│  │  │  └─ BookService.java
│  │  └─ domain/model/
│  │     └─ Book.java
│  └─ test/java/com/example/demo/
│     ├─ adapter/web/controller/
│     │  └─ BookControllerTest.java
│     └─ GreetingControllerTest.java
├─ pom.xml
└─ README.md

Architecture (current)

• Web adapter: adapter/web/controller/BookController
• DTOs (web layer): adapter/web/dtos/BookDtos (only used by controllers)
• Application layer: application/service/BookService — business orchestration; does not depend on web DTOs
• Domain model: domain/model/Book
• Port (outbound): application/portout/repository/BookRepository — domain-facing repository interface
• Greeting feature: GreetingController at the root of com.example.demo

Keep DTOs in the web adapter to avoid leaking HTTP shapes into the service/domain. Map to/from domain in the controller.

---

Prerequisites

• Java 17+ installed and JAVA_HOME set
• Maven or use the Maven Wrapper (recommended)

(Windows) One-time setup via PowerShell

# Verify
java -version
mvn -v

If Maven isn’t installed, generate the wrapper once (requires Maven available somewhere), or use IntelliJ’s bundled Maven.

---

Quick start

1) Install deps & run

# from project root (app/)
mvn clean package
mvn spring-boot:run

Alternatively, after packaging: java -jar target/simple-java-spring-boot-project-0.0.1-SNAPSHOT.jar

2) Smoke test

# curl
curl http://localhost:8080/greeting
curl "http://localhost:8080/greeting?name=BOM"

Expected

{"message":"Hello, World!"}
{"message":"Hello, BOM!"}

---

Configuration

src/main/resources/application.properties

spring.datasource.url=jdbc:h2:mem:demo;DB_CLOSE_DELAY=-1
spring.jpa.hibernate.ddl-auto=update
spring.h2.console.enabled=true
management.endpoints.web.exposure.include=health,info

• H2 console: http://localhost:8080/h2-console (JDBC URL: shown in logs or jdbc:h2:mem:demo)

---

API

Greeting

• GET /greeting → { "message": "Hello, World!" }
• GET /greeting?name=YourName → { "message": "Hello, YourName!" }

Book

Entity (Book.java)

@Entity
@Table(name = "book")
public class Book {
  @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long id;
  @Column(nullable=false) private String title;
  @Column(nullable=false) private String author;
  @Column(name="published_year") private Integer year; // avoid YEAR keyword in H2
  // constructors/getters/setters
}

Endpoints (controller paths prefix /api/books)

Method	Path	Body (JSON)	Response
POST	/api/books	{ "title":"DDD","author":"Evans","year":2003 }	201 Created + created resource
GET	/api/books/{id}	–	200 OK + book
PUT	/api/books/{id}	{ "title":"DDD 2e","author":"Evans","year":2015 }	200 OK + updated book
DELETE	/api/books/{id}	–	204 No Content

Example (PowerShell):

# create
irm -Method Post -ContentType 'application/json' `
  -Body '{"title":"DDD","author":"Evans","year":2003}' `
  http://localhost:8080/api/books

# get
irm http://localhost:8080/api/books/1

# update
irm -Method Put -ContentType 'application/json' `
  -Body '{"title":"DDD 2e","author":"Evans","year":2015}' `
  http://localhost:8080/api/books/1

# delete
Invoke-RestMethod -Method Delete http://localhost:8080/api/books/1

Validation

• DTOs use Jakarta Validation annotations (e.g., @NotBlank, @Min, @Max)
• Invalid input → 400 Bad Request with RFC7807 ProblemDetail (if @RestControllerAdvice is present)

---

Actuator

• /actuator/health → app health
• Expose more endpoints via management.endpoints.web.exposure.include

---

Testing

mvn -q clean test

GreetingControllerTest uses @WebMvcTest + MockMvc.

---

Packaging & Docker

# fat jar
mvn clean package
java -jar target/simple-java-spring-boot-project-0.0.1-SNAPSHOT.jar

# Build an OCI image (requires Docker)
mvn spring-boot:build-image -DskipTests
# Run it
docker run --rm -p 8080:8080 simple-java-spring-boot-project:0.0.1-SNAPSHOT

---

Troubleshooting

• Red annotations (@Entity, @Id, etc.) → ensure spring-boot-starter-data-jpa exists, Maven ⟳ reload, and correct imports jakarta.persistence.*.
• Package errors → disable Compact Middle Packages and ensure folders are nested: src/main/java/com/example/demo/....
• H2 DDL error about YEAR → we map year field to published_year via @Column(name="published_year").
• Duplicate dependency warning → keep only one <dependency> for spring-boot-starter-data-jpa in pom.xml.
• mvn/java not found in IntelliJ terminal → set JAVA_HOME, add Maven to PATH, or use Maven Wrapper; restart IDE to pick up env vars.

---

Next steps (optional)

• Add BookRepository, BookService, and controller tests
• Add OpenAPI: org.springdoc:springdoc-openapi-starter-webmvc-ui → /swagger-ui.html
• Switch to Postgres (prod): set spring.datasource.url, add driver org.postgresql:postgresql, and use Flyway for schema
• Observability: add metrics, logs JSON, request tracing (Micrometer + OpenTelemetry)

---

License

MIT (or your preferred license).