Apache Kafka提供了一个确切的一次事务（Exactly Once Transaction）功能，该功能确保了消息传递的精确性。同时，Kafka还提供了Fencing机制，以确保只有具有正确事务ID的生产者才能写入分区，并保证消费者仅读取可序列化的副本。Fencing机制的实现方式是在每个生产者发送消息时设置一个Epoch，用于监控生产者的状态。

下面的示例代码演示了如何使用Fencing机制来防止其他生产者在当前Epoch上写入分区，从而保证消息传递的准确性。

public class KafkaProducer {

    private static final String FENCED_PRODUCER_EPOCH_KEY = "fenced_producer_epoch";
    private static final int TIMEOUT_MILLIS = 1000;
    private static final int MAX_RETRIES = 10;
    private final String topic;
    private final KafkaProducer producer;
    private final String epoch;
    private final String transactionalId;

    public KafkaProducer(String bootstrapServers, String transactionalId, String topic) {
        Properties props = new Properties();
        props.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, bootstrapServers);
        props.put(ProducerConfig.TRANSACTIONAL_ID_CONFIG, transactionalId);
        props.put(ProducerConfig.ENABLE_IDEMPOTENCE_CONFIG, true);
        this.topic = topic;
        this.transactionalId = transactionalId;
        this.producer = new KafkaProducer<>(props, new StringSerializer(), new StringSerializer());

        // Generate a unique epoch for the FencedProducer
        String epoch = UUID.randomUUID().toString();
        this.epoch = epoch;

        // Store the epoch in the producer's configuration
        producer.configure(getProducerConfiguration(epoch));
        producer.initTransactions();
        producer.beginTransaction();
    }

    public void send(String key, String value) throws ProducerFencedException {
        try {
            producer.send(new ProducerRecord<>(topic, key, value)).get(TIMEOUT_MILLIS, TimeUnit.MILLISECONDS);
        } catch (InterruptedException | ExecutionException | TimeoutException e) {
            // The send request failed - rollback the transaction
            producer.abortTransaction();
            throw new ProducerFencedException("Producer failed to send message", e);
        }
    }

    private Properties getProducerConfiguration(String epoch) {
        Properties props = new Properties();
        props.put(ProducerConfig.TRANSACTIONAL_ID_CONFIG, transactionalId);
        props.put(FENCED_PRODUCER_EPOCH_KEY,