Sending and Receiving Transactional Messages

Preparing the Environment

You can connect open-source Java clients to DMS for RocketMQ. The recommended Java client version is 5.0.5.

<dependency>
    <groupId>org.apache.rocketmq</groupId>
    <artifactId>rocketmq-client-java</artifactId>
    <version>5.0.5</version>
</dependency>

Sending Transactional Messages

Refer to the following sample code or obtain more sample code from ProducerTransactionMessageExample.java.

import org.apache.rocketmq.client.apis.ClientConfiguration;
import org.apache.rocketmq.client.apis.ClientException;
import org.apache.rocketmq.client.apis.ClientServiceProvider;
import org.apache.rocketmq.client.apis.SessionCredentialsProvider;
import org.apache.rocketmq.client.apis.StaticSessionCredentialsProvider;
import org.apache.rocketmq.client.apis.message.Message;
import org.apache.rocketmq.client.apis.producer.Producer;
import org.apache.rocketmq.client.apis.producer.SendReceipt;
import org.apache.rocketmq.client.apis.producer.Transaction;
import org.apache.rocketmq.client.apis.producer.TransactionChecker;
import org.apache.rocketmq.client.apis.producer.TransactionResolution;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.IOException;
import java.nio.charset.StandardCharsets;

public class ProducerTransactionMessageExample {
    private static final Logger log = LoggerFactory.getLogger(ProducerTransactionMessageExample.class);

    public static void main(String[] args) throws ClientException, IOException {
        final ClientServiceProvider provider = ClientServiceProvider.loadService();

        String topic = "yourTransactionTopic";
        // Specify the gRPC address or gRPC public address
        String endpoints = "yourEndpoints";
        // Enter your username and key. Hard-coded or plaintext username and key are risky. You are advised to store them in ciphertext in a configuration file or an environment variable. The code below is required only if ACL was enabled during instance creation.
        String accessKey = System.getenv("ROCKETMQ_AK");
        String secretKey = System.getenv("ROCKETMQ_SK");
        SessionCredentialsProvider sessionCredentialsProvider =
                new StaticSessionCredentialsProvider(accessKey, secretKey);

        ClientConfiguration clientConfiguration = ClientConfiguration.newBuilder()
                .setEndpoints(endpoints)
                // .enableSsl(false)  // Disable SSL if has been enabled.
                // .setCredentialProvider(sessionCredentialsProvider)  // Set the credential provider if ACL has been enabled.
                .build();

        TransactionChecker checker = messageView -> {
            log.info("Receive transactional message check, message={}", messageView);
            // Return the transaction resolution according to your business logic.
            // Check the local transaction and return its status.
            return TransactionResolution.COMMIT;
        };
        final Producer producer = provider.newProducerBuilder()
                .setClientConfiguration(clientConfiguration)
                .setTopics(topic)
                // The producer needs to construct a transaction checker to check the intermediate status of abnormal transactions.
                .setTransactionChecker(checker)
                .build();
        byte[] body = "This is a transaction message for Apache RocketMQ".getBytes(StandardCharsets.UTF_8);
        String tag = "yourMessageTagA";
        final Message message = provider.newMessageBuilder()
                .setTopic(topic)
                .setTag(tag)
                .setKeys("yourMessageKey")
                .setBody(body)
                .build();
        // Start a transaction branch.
        final Transaction transaction;
        try {
            transaction = producer.beginTransaction();
        } catch (ClientException e) {
            log.error("Failed to begin transaction", e);
            // The transaction branch fails to be started and exits.
            return;
        }
        try {
            final SendReceipt sendReceipt = producer.send(message, transaction);
            log.info("Send transaction message successfully, messageId={}", sendReceipt.getMessageId());
        } catch (Throwable t) {
            log.error("Failed to send message", t);
            return;
        }
        /**
         * Execute a local transaction and check the result.
         * 1. Commit a transactional message if local transaction is committed.
         * 2. Rollback transaction if local transactional message fails to be committed.
         * 3. Wait for transaction re-check if unknown exception occurs.
         *
         */
        transaction.commit();
        // transaction.rollback();

        // Close the producer when it is no longer needed.
        producer.close();
    }
}

For transactional messages, the producer needs to construct a transaction checker to check the intermediate status of abnormal transactions. Three transaction statuses can be returned:

• TransactionResolution.COMMIT: Transaction committed. The consumer can retrieve the message.
• TransactionResolution.ROLLBACK: Transaction rolled back. The message will be discarded and cannot be retrieved.
• TransactionResolution.UNKNOWN: The status cannot be determined and the server is expected to check the message status from the producer again.

Subscribing to Transactional Messages

The code for subscribing to transactional messages is the same as that for subscribing to normal messages.