Creating Spring Boot Projects

Purpose

Use this skill to create new Spring Boot 4 projects or define their structure before implementation. The skill adds value when the user needs an architecture decision, Spring Boot 4 feature selection, or the bundled templates in assets/.

Critical rules

• Never jump straight to implementation before assessing project complexity.
• Default to the simplest architecture that fits the domain.
• Treat Spring Boot 4 as the target. Default new projects to Java 25 (current LTS). Boot 4's official baseline is Java 17 — accept Java 21 (previous LTS) or Java 17 when the user asks for them. Java 26 is the newest feature release (GA 2026-03-17) but is non-LTS; only pick it if the project tracks non-LTS Java.
• Read the reference files before choosing a higher-complexity architecture or optional framework feature.
• Reuse the templates in assets/ instead of rewriting the same scaffolding from scratch.

Workflow

Step 1: Assess project shape

Collect the project constraints first:

1. Domain complexity: simple CRUD, moderate workflow, or rich domain rules.
2. Team size: 1-3, 3-10, or 10+.
3. Expected lifespan: months, 1-2 years, or 5+ years.
4. Type-safety needs: basic validation or strong value-object-heavy modeling.
5. Bounded contexts: single domain or multiple feature areas.
6. Persistence and infrastructure needs: database choice, migration tool, local development setup.

Step 2: Choose the architecture

Use this matrix as the default decision aid. If the choice is not obvious, read references/architecture-guide.md before proceeding.

Pattern	Use when	Complexity
layered	CRUD services, prototypes, MVPs	Low
package-by-module	3-5 distinct features with moderate growth	Low-Medium
modular-monolith	Module boundaries matter and Spring Modulith is justified	Medium
tomato	Rich domain modeling, value objects, stronger type safety	Medium-High
ddd-hexagonal	Complex domains, CQRS, strong infrastructure isolation	High

tomato is a value-object-heavy modular monolith: JPA entities embed VOs, validation lives in VO constructors, and Spring converters bind VOs at the request boundary. See references/architecture-guide.md for the full definition.

Step 3: Define the initial Boot 4 setup

Use Spring Initializr and capture the baseline:

• Project: Maven or Gradle
• Language: Java
• Spring Boot: 4.1.x
• Java: 25 (recommended — current LTS). Boot 4's minimum is Java 17; use 21 for the previous LTS, or 17 for stricter compatibility. Java 26 (GA 2026-03-17) is the latest feature release but is non-LTS.

Baseline dependencies for most projects:

• Spring Web MVC
• Validation
• Spring Data JPA if persistence is required
• Flyway or Liquibase
• database driver
• Spring Boot Actuator
• Testcontainers for integration tests

Optional dependencies based on architecture or features:

• Spring Modulith for modular monolith or tomato designs
• ArchUnit for stronger architecture enforcement
• Additional Spring Boot 4 features only when the use case needs them

Read references/spring-boot-4-features.md before selecting:

• RestTestClient
• HTTP Service Clients
• API versioning
• JSpecify null-safety
• resilience features

Step 4: Apply the matching assets

Use the bundled templates from assets/ and replace placeholders only after the package and module names are settled.

Placeholder convention

Every template uses {{TOKEN}} placeholders. Resolve all of them before applying — templates do not compile until every placeholder is replaced. The full set used across assets/:

Placeholder	Replace with	Example
{{PACKAGE}}	Base Java package	com.acme.shop
{{MODULE}}	Feature/module name (lowercase)	orders
{{NAME}}	Domain type name (PascalCase)	Order, ProductSKU
{{TYPE}}	Wrapped scalar type inside a value object	String, Long, BigDecimal
{{FIELD}}	Record field name (camelCase)	code, amount
{{TABLE_NAME}}	Database table name (used in JPA @Table)	orders
{{TABLE}}	Same meaning as {{TABLE_NAME}} — legacy variant kept only in flyway-migration.sql	orders
{{PROJECT_NAME}}	Project artifactId / docker prefix (used only in docker-compose.yml)	shop-api
{{name}}	HTTP service group identifier — not a lowercase variant of {{NAME}}. Appears only in commented @ImportHttpServices(group = "...") examples.	orders

If a template uses a placeholder not listed here, treat it as a typo and confirm the intended value before applying.

Core project templates:

• assets/controller.java
• assets/repository.java
• assets/base-entity.java
• assets/rich-entity.java
• assets/value-object.java
• assets/spring-converter.java
• assets/service-cqrs.java
• assets/exception-handler.java
• assets/flyway-migration.sql
• assets/docker-compose.yml

Boot 4 and modularity templates:

• assets/http-service-client.java
• assets/api-versioning-config.java
• assets/resttestclient-test.java
• assets/package-info-jspecify.java
• assets/modularity-test.java
• assets/resilience-service.java
• assets/pom-additions.xml
• assets/testcontainers-test.java

Step 5: Fill in architecture-specific pieces

Read references/architecture-guide.md for package structure and apply the matching templates:

• layered: keep modules simple and avoid premature DDD abstractions
• package-by-module: group by feature and keep shared code minimal
• modular-monolith: add Modulith verification and explicit module APIs
• tomato: add value objects and rich domain entities where they protect important invariants
• ddd-hexagonal: separate application, domain, and infrastructure explicitly

Step 6: Hand off specialized concerns when needed

• Use spring-data-jpa when the user needs deeper query, projection, repository, or relationship decisions.
• Use springboot-migration for upgrades of existing applications rather than new-project setup.

Reference loading guide

• Package structures, anti-patterns, and upgrade paths: references/architecture-guide.md
• Spring Boot 4 feature-specific guidance: references/spring-boot-4-features.md

Output format

When the user asks for a plan or scaffold recommendation, return:

## Recommended architecture
- Pattern:
- Why:

## Initial setup
- Build tool:
- Java version:
- Spring Boot version:
- Core dependencies:

## Assets to apply
- `assets/...`

## Next implementation steps
1. ...
2. ...
3. ...

When not to use this skill

• Migrating an existing Boot project
• Deep repository and query tuning without broader project-creation work
• Generic Spring Boot feature Q&A with no need for the bundled templates