Java Client for UmaDB

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:0.2")

Apache Maven

<dependency>
    <groupId>io.github.domenicdev</groupId>
    <artifactId>umadb-java-client</artifactId>
    <version>0.2</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 API Key

To use a secured communication over TLS, simply enable TLS when building the UmaDbClient:

UmaDbClient client = UmaDbClient.builder()
        .withHost("localhost")
        .withPort(50051)
        .withTlsEnabled()
        .build();

client.connect();

You can also specify your own certificate authority like this (TLS will be automatically enabled):

UmaDbClient client = UmaDbClient.builder()
        .withHost("localhost")
        .withPort(50051)
        .withCertificateAuthority("server.pem")
        .build();

For API key-protected servers, use the withApiKey when building the client:

UmaDbClient client = UmaDbClient.builder()
        .withHost("localhost")
        .withPort(50051)
        .withApiKey("umadb:example-api-key-123456789")
        .build();

To specify both CA + API key, simply use the corresponding builder methods:

UmaDbClient client = UmaDbClient.builder()
        .withHost("localhost")
        .withPort(50051)
        .withCertificateAuthority("server.pem")
        .withApiKey("umadb:example-api-key-123456789")
        .build();

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