Consumer

Overview

Module

• package: org.eclipse.dirigible.sdk.messaging
• source: messaging/Consumer.java

Synchronously pulls a single message from a queue or topic, blocking up to timeoutMillis. Returns null when the timeout elapses without a delivery.

Use this in script-style code that processes a single message and exits, or when you want tight backpressure control. For long-running, always-on consumption use a @Listener-annotated class — the platform manages the consumer thread, reconnects, and ordering for you.

Key Features:

• Blocking Pull: Each call blocks the caller until a message arrives or the supplied timeout elapses.
• Queue and Topic Support: Separate methods cover point-to-point queue consumption and publish-subscribe topic consumption.
• Null on Timeout: An empty queue / topic at timeout produces a null return value rather than an exception, so callers can drive a polling loop without try/catch.

Example Usage:

import org.eclipse.dirigible.sdk.messaging.Consumer;

// Wait up to 5 seconds for the next message on the 'orders.created' queue.
String message = Consumer.receiveFromQueue("orders.created", 5000L);
if (message != null) {
    System.out.println("Received: " + message);
}

// Poll a topic with a 1-second deadline per call.
String tick = Consumer.receiveFromTopic("metrics.heartbeat", 1000L);

Methods

receiveFromQueue()

Blocks up to timeoutMillis waiting for a single message on the named queue. The message is removed from the queue when consumed.

public static String receiveFromQueue(String queue, long timeoutMillis);

Parameter	Type	Description
queue	String	Logical name of the queue destination.
timeoutMillis	long	Maximum time to wait, in milliseconds.

Returns

• Type: String
• Description: The message payload, or null if the timeout elapses without a delivery.

receiveFromTopic()

Blocks up to timeoutMillis waiting for a single message on the named topic.

public static String receiveFromTopic(String topic, long timeoutMillis);

Parameter	Type	Description
topic	String	Logical name of the topic destination.
timeoutMillis	long	Maximum time to wait, in milliseconds.

Returns

• Type: String
• Description: The message payload, or null if the timeout elapses without a delivery.