The Cratis Java Application template

The cratis-java template is the Java flavor of the full-stack starting point. One command gives you a running application with the whole stack wired: Arc for commands and queries over HTTP, Chronicle for the event log, MongoDB for read models, and a React frontend that talks to generated TypeScript proxies — all authored in Java on Spring Boot.

Install the package and scaffold:

dotnet new install Cratis.Templates.Java
dotnet new cratis-java -n MyStore

MongoDB is the default database. Pass --Database to scaffold against PostgreSQL, MsSql, or SQLite instead — the docker-compose.yml then provisions the matching database for the Chronicle kernel, and the read-model sink switches to SQL:

dotnet new cratis-java -n MyStore --Database PostgreSQL

The application code itself is identical for all databases — read models are persisted by the Chronicle kernel, so only the infrastructure the kernel runs against changes.

What you get

MyStore/
├── build.gradle.kts           — Gradle build with the Arc plugin
├── settings.gradle.kts        — plugin and dependency repositories
├── gradlew, gradle/wrapper/   — Gradle wrapper (9.1.0)
├── docker-compose.yml         — Chronicle dev container + Aspire dashboard
├── package.json               — frontend tooling (Vite, React, Cratis Components)
├── .frontend/                 — Vite and TypeScript configuration
├── App.tsx, Home.tsx          — frontend application shell
├── SomeModule/                — the sample frontend slices
└── src/main/
    ├── java/com/example/
    │   ├── CratisAppApplication.java   — Spring Boot entry point
    │   ├── ChronicleConfiguration.java — Chronicle options and artifact registration
    │   └── somemodule/                 — the sample backend vertical slices
    └── kotlin/com/example/PackageMarker.kt — keeps the package visible for KSP

The sample slices teach the conventions

The Registration slice shows the command side — a @Command record with a @CommandKey, returning the event to append through Arc’s Java asynchronous command path. No controller, no route registration:

@Command
@AllowAnonymous
public record Register(@CommandKey SomeId id, SomeName name) {
    public CompletionStage<Registered> handle() {
        return CompletableFuture.completedFuture(new Registered(name()));
    }
}

SomeId is a strongly-typed identity — a record implementing ConceptAs<String> — rather than a raw String. The command key routes the command to its event source; the generated TypeScript command sends it as part of the payload.

The Listing slice shows the read side — a read model record built by a @Reducer from the Registered event, with a query exposing it over HTTP:

@io.cratis.arc.artifacts.ReadModel
@io.cratis.chronicle.readModels.ReadModel
@AllowAnonymous
public record Listing(String id, SomeName name) {
    @Path("/api/listings")
    public static CompletionStage<List<Listing>> all(@FromServices Chronicle chronicle) {
        return CompletableFuture.completedFuture(chronicle.readModels(Listing.class));
    }
}

Post to the command route and the whole loop runs — command handled, event appended to Chronicle, reactor notified, read model updated:

curl -sS -X POST http://localhost:8080/api/register \
    -H 'Content-Type: application/json' \
    -d '{"id":"'$(uuidgen)'","name":"Cratis"}'

curl -sS -X QUERY http://localhost:8080/api/listings \
    -H 'Content-Type: application/json' \
    -d '{"arguments":{}}'

Versions

The template pins the versions it was verified against — Arc 7.2.0 (Gradle plugin and arc-chronicle-spring-boot-starter, which pins Chronicle 4.0.0), Kotlin 2.4.20, Spring Boot 4.1.1, JDK 17, and Gradle 9.1.0. Upgrade by bumping these in build.gradle.kts, keeping the plugin and starter versions in sync.

AI assistance

The scaffolded project includes a .cratis/ai.json with the Cratis AI profiles, languages, and coding agent harnesses for this template — the Cratis application selection for the JVM clients, with the Java, Kotlin, and TypeScript languages. Make sure the Cratis CLI is installed, then run:

cratis ai update

See the CLI AI documentation for the full command reference.