Chronicle Kotlin Client

The Chronicle Kotlin client is the JVM SDK for Chronicle. It wraps the Chronicle gRPC contracts with Kotlin-native constructs such as coroutines, data classes, and annotations.

Use this section for Kotlin and Java setup, runtime integration, annotations, and API reference details. Shared Chronicle concepts and workflows live in the main Chronicle docs and use language tabs when code differs by client.

Shared Chronicle topics

• Get started
• Events and event logs
• Appending events
• Read models
• Projections
• Reactors
• Reducers
• Constraints
• Event seeding
• Compliance
• Transactions and unit of work
• Event evolution

Kotlin and Java setup

You need a running Chronicle Kernel. The simplest way is Docker Compose. Chronicle serves gRPC, the API, and health checks on port 35000 over TLS with a self-signed development certificate:

services:
  chronicle:
    image: cratis/chronicle:latest-development-slim
    depends_on:
      - mongodb
      - mongodb-init
    environment:
      - ASPNETCORE_ENVIRONMENT=Development
      - Cratis__Chronicle__Storage__Type=MongoDB
      - Cratis__Chronicle__Storage__ConnectionDetails=mongodb://mongodb:27017/?directConnection=true
    ports:
      - "35000:35000"

  mongodb:
    image: mongo:8
    command: ["mongod", "--replSet", "rs0", "--bind_ip_all"]
    ports:
      - "27017:27017"

  # Chronicle's MongoDB storage needs a replica set — initiate it once.
  mongodb-init:
    image: mongo:8
    depends_on:
      - mongodb
    restart: "no"
    command:
      - /bin/bash
      - -lc
      - |
        until mongosh --host mongodb --quiet \
          --eval "db.adminCommand('ping')" >/dev/null 2>&1; do
          sleep 1
        done
        mongosh --host mongodb --quiet --eval "
        try {
          rs.status();
        } catch (e) {
          rs.initiate({
            _id: 'rs0',
            members: [{ _id: 0, host: 'mongodb:27017' }]
          });
        }"

Chronicle is ready once curl -sk https://localhost:35000/health reports Healthy. The Samples/Kotlin/Console and Samples/Java/Console folders in the repository contain this file along with PostgreSQL, SQL Server, and SQLite profiles.

Then add the client to your Gradle build:

dependencies {
    implementation("io.cratis:chronicle:2.1.2")
}

The same JVM client supports both Kotlin and Java. Shared pages include separate Kotlin and Java tabs when both examples exist.

Client-specific pages

• Get Started — install the JVM client, connect, and run a small Kotlin flow
• Reference — annotations, configuration, and service API details