Pulsar transaction is primarily a server-side and protocol-level feature. This tutorial guides you through every step of how to use the Pulsar transaction API to send and receive messages in a Java client.
note
Currently, Pulsar transaction API is available in Pulsar 2.8.0 or later versions. It is only available for Java clients.
//mandatory configuration, used to enable transaction coordinator transactionCoordinatorEnabled=true //mandatory configuration, used to create systemTopic used for transaction buffer snapshot systemTopicEnabled=true
note
By default, Pulsar transactions are disabled.
Initialize transaction coordinator metadata.
The transaction coordinator can leverage the advantages of partitioned topics (such as load balance).
Currently, messages can be acked individually rather than cumulatively.
End transactions.
tip
The code snippet below is the example for step 3 - step 8.
Input
PulsarClient client =PulsarClient.builder() // Step 3: create a Pulsar client and enable transactions. .enableTransaction(true) .serviceUrl(jct.serviceUrl) .build(); // Step 4: create three producers to produce messages to input and output topics. ProducerBuilder<String> producerBuilder = client.newProducer(Schema.STRING); Producer<String> inputProducer = producerBuilder.topic(inputTopic) .sendTimeout(0,TimeUnit.SECONDS).create(); Producer<String> outputProducerOne = producerBuilder.topic(outputTopicOne) .sendTimeout(0,TimeUnit.SECONDS).create(); Producer<String> outputProducerTwo = producerBuilder.topic(outputTopicTwo) .sendTimeout(0,TimeUnit.SECONDS).create(); // Step 4: create three consumers to consume messages from input and output topics. Consumer<String> inputConsumer = client.newConsumer(Schema.STRING) .subscriptionName("your-subscription-name").topic(inputTopic).subscribe(); Consumer<String> outputConsumerOne = client.newConsumer(Schema.STRING) .subscriptionName("your-subscription-name").topic(outputTopicOne).subscribe(); Consumer<String> outputConsumerTwo = client.newConsumer(Schema.STRING) .subscriptionName("your-subscription-name").topic(outputTopicTwo).subscribe(); int count =2; // Step 5: produce messages to input topics. for(int i =0; i < count; i++){ inputProducer.send("Hello Pulsar! count : "+ i); } // Step 5: consume messages and produce them to output topics with transactions. for(int i =0; i < count; i++){ // Step 5: the consumer successfully receives messages. Message<String> message = inputConsumer.receive(); // Step 6: create transactions. // The transaction timeout is specified as 10 seconds. // If the transaction is not committed within 10 seconds, the transaction is automatically aborted. Transaction txn =null; try{ txn = client.newTransaction() .withTransactionTimeout(10,TimeUnit.SECONDS).build().get(); // Step 6: you can process the received message with your use case and business logic. // Step 7: the producers produce messages to output topics with transactions outputProducerOne.newMessage(txn).value("Hello Pulsar! outputTopicOne count : "+ i).send(); outputProducerTwo.newMessage(txn).value("Hello Pulsar! outputTopicTwo count : "+ i).send(); // Step 7: the consumers acknowledge the input message with the transactions *individually*. inputConsumer.acknowledgeAsync(message.getMessageId(), txn).get(); // Step 8: commit transactions. txn.commit().get(); }catch(ExecutionException e){ if(!(e.getCause()instanceofPulsarClientException.TransactionConflictException)){ // If TransactionConflictException is not thrown, // you need to redeliver or negativeAcknowledge this message, // or else this message will not be received again. inputConsumer.negativeAcknowledge(message); } // If a new transaction is created, // then the old transaction should be aborted. if(txn !=null){ txn.abort(); } } } // Final result: consume messages from output topics and print them. for(int i =0; i < count; i++){ Message<String> message = outputConsumerOne.receive(); System.out.println("Receive transaction message: "+ message.getValue()); } for(int i =0; i < count; i++){ Message<String> message = outputConsumerTwo.receive(); System.out.println("Receive transaction message: "+ message.getValue()); } } }