kafka-client的版本:0.10有个很重要的类Partitioner
List-1
代码语言：javascript复制public interface Partitioner extends Configurable {
/**
* 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 The serialized key to partition on( or null if no key)
* @param value The value to partition on or null
* @param valueBytes The 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);
public void close();
}如List-1所示，发送消息时，传入到partition方法中，返回的int值就是分区号，即发送到哪个分区，默认的实现是DefaultPartitioner，如下List-2
List-2
代码语言：javascript复制public class DefaultPartitioner implements Partitioner {
private final AtomicInteger counter = new AtomicInteger(new Random().nextInt());
private static int toPositive(int number) {
return number & 0x7fffffff;
}
public void configure(Map<String, ?> configs) {}
/**
* 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) {
//1获取所有的分区信息
List<PartitionInfo> partitions = cluster.partitionsForTopic(topic);
int numPartitions = partitions.size();
if (keyBytes == null) {
//2如果没有指定key
int nextValue = counter.getAndIncrement();
List<PartitionInfo> availablePartitions = cluster.availablePartitionsForTopic(topic);
if (availablePartitions.size() > 0) {
//3
int part = DefaultPartitioner.toPositive(nextValue) % availablePartitions.size();
return availablePartitions.get(part).partition();
} else {
// no partitions are available, give a non-available partition
//4
return DefaultPartitioner.toPositive(nextValue) % numPartitions;
}
} else {
// hash the keyBytes to choose a partition
//5 如果有key,那么根据key进行hash计算得到hash值，之后对分区数取模
return DefaultPartitioner.toPositive(Utils.murmur2(keyBytes)) % numPartitions;
}
}
public void close() {}
}- 从cluster中获取集群的分区信息
- 如果我们没有指定消息key，那个获取下一个递增int值
- 3和4中，用递增值对分区数取模，这样达到轮询发送到各个分区
- 如果指定了指定了key，那么对key取hash值，之后用hash值对分区数取模
所以如果没有指定key，那么使用轮询发送到各个分区；如果指定了key，那么同key的发送到相同的分区
如果我们想随机发送到分区，那个我们应该实现这个接口，而后指定使用这个分区算法。
