public Iterable<ConsumerRecord<K, V>> records(String topic) {
        if (topic == null)
            throw new IllegalArgumentException("Topic must be non-null.");
        List<List<ConsumerRecord<K, V>>> recs = new ArrayList<>();
        for (Map.Entry<TopicPartition, List<ConsumerRecord<K, V>>> entry : records.entrySet()) {
            if (entry.getKey().topic().equals(topic))
                recs.add(entry.getValue());
        }
        return new ConcatenatedIterable<>(recs);
    }
Get just the records for the given topic
clients/src/main/java/org/apache/kafka/clients/consumer/ConsumerRecords.java