This is your first hands-on lesson with the Java SDK: create a client, send an event, and receive it. Make sure you have the SDK installed (see the Java SDK overview).

Create a Client

The Java SDK provides pattern-specific client classes:

Connect.java

import io.kubemq.sdk.pubsub.PubSubClient;

PubSubClient client = PubSubClient.builder()
    .address("localhost:50000")
    .clientId("my-service")
    .build();

System.out.println("Connected to KubeMQ");
client.close();

Client Class	Use For
`PubSubClient`	Events, Events Store
`QueuesClient`	Queues
`CQClient`	Commands, Queries (RPC)

Send Your First Event

SendEvent.java

PubSubClient client = PubSubClient.builder()
    .address("localhost:50000")
    .clientId("events-sender")
    .build();

client.publishEvent(EventMessage.builder()
    .channel("notifications")
    .body("hello kubemq".getBytes())
    .build());
System.out.println("Event sent to 'notifications'");
client.close();

Receive Events

ReceiveEvents.java

PubSubClient client = PubSubClient.builder()
    .address("localhost:50000")
    .clientId("events-receiver")
    .build();

client.subscribeToEvents(EventsSubscription.builder()
    .channel("notifications")
    .onReceiveEventCallback(event ->
        System.out.println("Received: " + new String(event.getBody())))
    .onErrorCallback(err ->
        System.err.println("Error: " + err.getMessage()))
    .build());

try {
    Thread.sleep(30000); // Keep listening
} catch (InterruptedException e) {
    Thread.currentThread().interrupt();
}
client.close();

Configuration Options

Parameter	Type	Default	Description
`address`	`String`	`localhost:50000`	KubeMQ server address
`clientId`	`String`	Auto-generated UUID	Unique client identifier
`authToken`	`String`	`null`	JWT authentication token
`tls`	`boolean`	`false`	Enable TLS encryption
`tlsCertFile`	`String`	`null`	TLS certificate file (PEM)
`tlsKeyFile`	`String`	`null`	TLS private key file (PEM)
`caCertFile`	`String`	`null`	CA certificate file
`maxReceiveSize`	`int`	`104857600`	Max inbound message size (100MB)
`reconnectIntervalSeconds`	`int`	`1`	Reconnection interval
`logLevel`	`Level`	`INFO`	Logging level

TLS setup is covered on its own page — see TLS Setup for a full example configuring tls, tlsCertFile, tlsKeyFile, and caCertFile.

Error Handling

The SDK uses a typed exception hierarchy rooted at KubeMQException:

ErrorHandling.java

try {
    client.publishEvent(message);
} catch (ConnectionException e) {
    System.err.println("Connection failed (retryable): " + e.getMessage());
} catch (AuthenticationException e) {
    System.err.println("Auth failed: " + e.getMessage());
} catch (ValidationException e) {
    System.err.println("Invalid request: " + e.getMessage());
} catch (KubeMQException e) {
    System.err.println("SDK error: " + e.getMessage());
}

Exception	Retryable	When
`ConnectionException`	Yes	Server unavailable
`KubeMQTimeoutException`	Yes	Deadline exceeded
`AuthenticationException`	No	Invalid credentials
`AuthorizationException`	No	Insufficient permissions
`ValidationException`	No	Invalid parameters

Next Steps

Java SDK Reference — full API documentation
Java SDK Examples — complete examples for all patterns
GitHub Repository — source code and issues

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