private final String topic;//所要发送的topic private final Integer partition;//指定的partition序号 private final Headers headers;//一组键值对,与RabbitMQ中的headers类似,kafka0.11.x版本才引入的一个属性 private final K key;//消息的key private final V value;//消息的value,即消息体 private final Long timestamp;//消息的时间戳,可以分为Create_Time和LogAppend_Time之分,这个以后的文章中再表。
/** * computes partition for given record. * if the record has partition returns the value otherwise * calls configured partitioner class to compute the partition. */ private int partition(ProducerRecord<K, V> record, byte[] serializedKey, byte[] serializedValue, Cluster cluster) { Integer partition = record.partition(); return partition != null ? partition : partitioner.partition(record.topic(), record.key(), serializedKey, record.value(), serializedValue, cluster); }
/** * Compute the partition for the given record. * * @param topic The topic name * @param key The key to partition on (or null if no key) * @param keyBytes serialized key to partition on (or null if no key) * @param value The value to partition on or null * @param valueBytes serialized value to partition on or null * @param cluster The current cluster metadata */ public int partition(String topic, Object key, byte[] keyBytes, Object value, byte[] valueBytes, Cluster cluster) { List<PartitionInfo> partitions = cluster.partitionsForTopic(topic); int numPartitions = partitions.size(); if (keyBytes == null) { int nextValue = nextValue(topic); List<PartitionInfo> availablePartitions = cluster.availablePartitionsForTopic(topic); if (availablePartitions.size() > 0) { int part = Utils.toPositive(nextValue) % availablePartitions.size(); return availablePartitions.get(part).partition(); } else { // no partitions are available, give a non-available partition return Utils.toPositive(nextValue) % numPartitions; } } else { // hash the keyBytes to choose a partition return Utils.toPositive(Utils.murmur2(keyBytes)) % numPartitions; } }
private int nextValue(String topic) { AtomicInteger counter = topicCounterMap.get(topic); if (null == counter) { counter = new AtomicInteger(ThreadLocalRandom.current().nextInt()); AtomicInteger currentCounter = topicCounterMap.putIfAbsent(topic, counter); if (currentCounter != null) { counter = currentCounter; } } return counter.getAndIncrement(); }