Java Client

A lightweight Java client for interacting with the UmaDB event store via gRPC, supporting event appends, queries, and live event streaming.

Developed and maintained by Domenic Cassisi.

Installation

Add the following dependency to either the build.gradle or pom.xml file in your project.

Gradle

implementation("io.github.domenicdev:umadb-java-client:0.1")

Apache Maven

<dependency>
    <groupId>io.github.domenicdev</groupId>
    <artifactId>umadb-java-client</artifactId>
    <version>0.1</version>
</dependency>

Getting Started

Basic Usage Example

import io.umadb.client.*;

import java.nio.charset.StandardCharsets;
import java.util.Iterator;
import java.util.List;

public final class UmaDbExample {

    public static void main(String[] args) {
        // ---------------------------------------------------------------------
        // 1. Create and connect the client
        // ---------------------------------------------------------------------
        UmaDbClient client = UmaDbClient.builder()
                .withHost("localhost")
                .withPort(50051)
                .build();

        client.connect();

        try {
            // -----------------------------------------------------------------
            // 2. Append an event
            // -----------------------------------------------------------------
            Event event = Event.of(
                    "user-created",
                    List.of("users", "important"),
                    "Hello UmaDB!".getBytes(StandardCharsets.UTF_8)
            );

            AppendRequest appendRequest = new AppendRequest(
                    List.of(event),
                    null // no append condition
            );

            AppendResponse appendResponse = client.handle(appendRequest);
            System.out.println("Event appended at position: " + appendResponse.position());

            // -----------------------------------------------------------------
            // 3. Read events
            // -----------------------------------------------------------------
            ReadRequest readRequest = new ReadRequest(
                    null,   // no query (read all events)
                    0L,     // start from the beginning
                    false,  // forwards
                    10,     // limit
                    false,  // do not subscribe
                    null
            );

            Iterator<ReadResponse> readIterator = client.handle(readRequest);

            while (readIterator.hasNext()) {
                ReadResponse response = readIterator.next();
                response.events().forEach(sequencedEvent -> {
                    System.out.println(
                            "Read event at position "
                                    + sequencedEvent.position()
                                    + " of type "
                                    + sequencedEvent.event().type()
                    );
                });
            }

            // -----------------------------------------------------------------
            // 4. Subscribe to new events (streaming)
            // -----------------------------------------------------------------
            long startPosition = client.getHeadPosition();

            ReadRequest subscribeRequest = new ReadRequest(
                    null,          // no query
                    startPosition, // start from current head
                    false,
                    null,          // unlimited
                    true,          // subscribe
                    null
            );

            Iterator<ReadResponse> subscription = client.handle(subscribeRequest);

            System.out.println("Subscribed to new events...");
            while (subscription.hasNext()) {
                ReadResponse response = subscription.next();
                response.events().forEach(sequencedEvent -> {
                    System.out.println(
                            "Received new event at position "
                                    + sequencedEvent.position()
                                    + " of type "
                                    + sequencedEvent.event().type()
                    );
                });
            }

        } finally {
            // -----------------------------------------------------------------
            // 5. Shutdown
            // -----------------------------------------------------------------
            client.shutdown();
        }
    }
}

Using TLS and an API key

For secured deployments (TLS + API key), the builder makes this explicit and safe:

UmaDbClient client = UmaDbClient.builder()
        .withHost("localhost")
        .withPort(50051)
        .withTlsAndApiKey(
                "server.pem",                       // CA certificate
                "umadb:example-api-key-123456789"   // API key
        )
        .build();

client.connect();

⚠️ Important: An API key requires TLS. The client will fail fast if an API key is provided without TLS.

Conditional append (optimistic concurrency)

QueryItem boundary = QueryItem.ofTypesAndTags(
        List.of("order-created"),
        List.of("order-123")
);

Query query = Query.of(boundary);

long lastKnownPosition = client.getHeadPosition();

AppendCondition condition = AppendCondition
        .failIfExists(query)
        .after(lastKnownPosition);

AppendRequest request = new AppendRequest(
        List.of(
                Event.of(
                        "order-created",
                        List.of("order-123"),
                        "Order created".getBytes(StandardCharsets.UTF_8)
                )
        ),
        condition
);

client.handle(request);

If a matching event already exists after the given position, the append will fail with:

UmaDbException.IntegrityException

---

Planned for Future Versions

• Async client